luci-base: form.js: ListValue: support widget and orientation properties

[project/luci.git] / modules / luci-base / htdocs / luci-static / resources / form.js

'use strict';
'require ui';
'require uci';
'require rpc';
'require dom';
'require baseclass';

var scope = this;

var callSessionAccess = rpc.declare({
        object: 'session',
        method: 'access',
        params: [ 'scope', 'object', 'function' ],
        expect: { 'access': false }
});

var CBIJSONConfig = baseclass.extend({
        __init__: function(data) {
                data = Object.assign({}, data);

                this.data = {};

                var num_sections = 0,
                    section_ids = [];

                for (var sectiontype in data) {
                        if (!data.hasOwnProperty(sectiontype))
                                continue;

                        if (L.isObject(data[sectiontype])) {
                                this.data[sectiontype] = Object.assign(data[sectiontype], {
                                        '.anonymous': false,
                                        '.name': sectiontype,
                                        '.type': sectiontype
                                });

                                section_ids.push(sectiontype);
                                num_sections++;
                        }
                        else if (Array.isArray(data[sectiontype])) {
                                for (var i = 0, index = 0; i < data[sectiontype].length; i++) {
                                        var item = data[sectiontype][i],
                                            anonymous, name;

                                        if (!L.isObject(item))
                                                continue;

                                        if (typeof(item['.name']) == 'string') {
                                                name = item['.name'];
                                                anonymous = false;
                                        }
                                        else {
                                                name = sectiontype + num_sections;
                                                anonymous = true;
                                        }

                                        if (!this.data.hasOwnProperty(name))
                                                section_ids.push(name);

                                        this.data[name] = Object.assign(item, {
                                                '.index': num_sections++,
                                                '.anonymous': anonymous,
                                                '.name': name,
                                                '.type': sectiontype
                                        });
                                }
                        }
                }

                section_ids.sort(L.bind(function(a, b) {
                        var indexA = (this.data[a]['.index'] != null) ? +this.data[a]['.index'] : 9999,
                            indexB = (this.data[b]['.index'] != null) ? +this.data[b]['.index'] : 9999;

                        if (indexA != indexB)
                                return (indexA - indexB);

                        return (a > b);
                }, this));

                for (var i = 0; i < section_ids.length; i++)
                        this.data[section_ids[i]]['.index'] = i;
        },

        load: function() {
                return Promise.resolve(this.data);
        },

        save: function() {
                return Promise.resolve();
        },

        get: function(config, section, option) {
                if (section == null)
                        return null;

                if (option == null)
                        return this.data[section];

                if (!this.data.hasOwnProperty(section))
                        return null;

                var value = this.data[section][option];

                if (Array.isArray(value))
                        return value;

                if (value != null)
                        return String(value);

                return null;
        },

        set: function(config, section, option, value) {
                if (section == null || option == null || option.charAt(0) == '.')
                        return;

                if (!this.data.hasOwnProperty(section))
                        return;

                if (value == null)
                        delete this.data[section][option];
                else if (Array.isArray(value))
                        this.data[section][option] = value;
                else
                        this.data[section][option] = String(value);
        },

        unset: function(config, section, option) {
                return this.set(config, section, option, null);
        },

        sections: function(config, sectiontype, callback) {
                var rv = [];

                for (var section_id in this.data)
                        if (sectiontype == null || this.data[section_id]['.type'] == sectiontype)
                                rv.push(this.data[section_id]);

                rv.sort(function(a, b) { return a['.index'] - b['.index'] });

                if (typeof(callback) == 'function')
                        for (var i = 0; i < rv.length; i++)
                                callback.call(this, rv[i], rv[i]['.name']);

                return rv;
        },

        add: function(config, sectiontype, sectionname) {
                var num_sections_type = 0, next_index = 0;

                for (var name in this.data) {
                        num_sections_type += (this.data[name]['.type'] == sectiontype);
                        next_index = Math.max(next_index, this.data[name]['.index']);
                }

                var section_id = sectionname || sectiontype + num_sections_type;

                if (!this.data.hasOwnProperty(section_id)) {
                        this.data[section_id] = {
                                '.name': section_id,
                                '.type': sectiontype,
                                '.anonymous': (sectionname == null),
                                '.index': next_index + 1
                        };
                }

                return section_id;
        },

        remove: function(config, section) {
                if (this.data.hasOwnProperty(section))
                        delete this.data[section];
        },

        resolveSID: function(config, section_id) {
                return section_id;
        },

        move: function(config, section_id1, section_id2, after) {
                return uci.move.apply(this, [config, section_id1, section_id2, after]);
        }
});

/**
 * @class AbstractElement
 * @memberof LuCI.form
 * @hideconstructor
 * @classdesc
 *
 * The `AbstractElement` class serves as abstract base for the different form
 * elements implemented by `LuCI.form`. It provides the common logic for
 * loading and rendering values, for nesting elements and for defining common
 * properties.
 *
 * This class is private and not directly accessible by user code.
 */
var CBIAbstractElement = baseclass.extend(/** @lends LuCI.form.AbstractElement.prototype */ {
        __init__: function(title, description) {
                this.title = title || '';
                this.description = description || '';
                this.children = [];
        },

        /**
         * Add another form element as children to this element.
         *
         * @param {AbstractElement} element
         * The form element to add.
         */
        append: function(obj) {
                this.children.push(obj);
        },

        /**
         * Parse this elements form input.
         *
         * The `parse()` function recursively walks the form element tree and
         * triggers input value reading and validation for each encountered element.
         *
         * Elements which are hidden due to unsatisified dependencies are skipped.
         *
         * @returns {Promise<void>}
         * Returns a promise resolving once this element's value and the values of
         * all child elements have been parsed. The returned promise is rejected
         * if any parsed values are not meeting the validation constraints of their
         * respective elements.
         */
        parse: function() {
                var args = arguments;
                this.children.forEach(function(child) {
                        child.parse.apply(child, args);
                });
        },

        /**
         * Render the form element.
         *
         * The `render()` function recursively walks the form element tree and
         * renders the markup for each element, returning the assembled DOM tree.
         *
         * @abstract
         * @returns {Node|Promise<Node>}
         * May return a DOM Node or a promise resolving to a DOM node containing
         * the form element's markup, including the markup of any child elements.
         */
        render: function() {
                L.error('InternalError', 'Not implemented');
        },

        /** @private */
        loadChildren: function(/* ... */) {
                var tasks = [];

                if (Array.isArray(this.children))
                        for (var i = 0; i < this.children.length; i++)
                                if (!this.children[i].disable)
                                        tasks.push(this.children[i].load.apply(this.children[i], arguments));

                return Promise.all(tasks);
        },

        /** @private */
        renderChildren: function(tab_name /*, ... */) {
                var tasks = [],
                    index = 0;

                if (Array.isArray(this.children))
                        for (var i = 0; i < this.children.length; i++)
                                if (tab_name === null || this.children[i].tab === tab_name)
                                        if (!this.children[i].disable)
                                                tasks.push(this.children[i].render.apply(
                                                        this.children[i], this.varargs(arguments, 1, index++)));

                return Promise.all(tasks);
        },

        /**
         * Strip any HTML tags from the given input string.
         *
         * @param {string} input
         * The input string to clean.
         *
         * @returns {string}
         * The cleaned input string with HTML removes removed.
         */
        stripTags: function(s) {
                if (typeof(s) == 'string' && !s.match(/[<>]/))
                        return s;

                var x = E('div', {}, s);
                return x.textContent || x.innerText || '';
        },

        /**
         * Format the given named property as title string.
         *
         * This function looks up the given named property and formats its value
         * suitable for use as element caption or description string. It also
         * strips any HTML tags from the result.
         *
         * If the property value is a string, it is passed to `String.format()`
         * along with any additional parameters passed to `titleFn()`.
         *
         * If the property value is a function, it is invoked with any additional
         * `titleFn()` parameters as arguments and the obtained return value is
         * converted to a string.
         *
         * In all other cases, `null` is returned.
         *
         * @param {string} property
         * The name of the element property to use.
         *
         * @param {...*} fmt_args
         * Extra values to format the title string with.
         *
         * @returns {string|null}
         * The formatted title string or `null` if the property did not exist or
         * was neither a string nor a function.
         */
        titleFn: function(attr /*, ... */) {
                var s = null;

                if (typeof(this[attr]) == 'function')
                        s = this[attr].apply(this, this.varargs(arguments, 1));
                else if (typeof(this[attr]) == 'string')
                        s = (arguments.length > 1) ? ''.format.apply(this[attr], this.varargs(arguments, 1)) : this[attr];

                if (s != null)
                        s = this.stripTags(String(s)).trim();

                if (s == null || s == '')
                        return null;

                return s;
        }
});

/**
 * @constructor Map
 * @memberof LuCI.form
 * @augments LuCI.form.AbstractElement
 *
 * @classdesc
 *
 * The `Map` class represents one complete form. A form usually maps one UCI
 * configuraton file and is divided into multiple sections containing multiple
 * fields each.
 *
 * It serves as main entry point into the `LuCI.form` for typical view code.
 *
 * @param {string} config
 * The UCI configuration to map. It is automatically loaded along when the
 * resulting map instance.
 *
 * @param {string} [title]
 * The title caption of the form. A form title is usually rendered as separate
 * headline element before the actual form contents. If omitted, the
 * corresponding headline element will not be rendered.
 *
 * @param {string} [description]
 * The description text of the form which is usually rendered as text
 * paragraph below the form title and before the actual form conents.
 * If omitted, the corresponding paragraph element will not be rendered.
 */
var CBIMap = CBIAbstractElement.extend(/** @lends LuCI.form.Map.prototype */ {
        __init__: function(config /*, ... */) {
                this.super('__init__', this.varargs(arguments, 1));

                this.config = config;
                this.parsechain = [ config ];
                this.data = uci;
        },

        /**
         * Toggle readonly state of the form.
         *
         * If set to `true`, the Map instance is marked readonly and any form
         * option elements added to it will inherit the readonly state.
         *
         * If left unset, the Map will test the access permission of the primary
         * uci configuration upon loading and mark the form readonly if no write
         * permissions are granted.
         *
         * @name LuCI.form.Map.prototype#readonly
         * @type boolean
         */

        /**
         * Find all DOM nodes within this Map which match the given search
         * parameters. This function is essentially a convenience wrapper around
         * `querySelectorAll()`.
         *
         * This function is sensitive to the amount of arguments passed to it;
         * if only one argument is specified, it is used as selector-expression
         * as-is. When two arguments are passed, the first argument is treated
         * as attribute name, the second one as attribute value to match.
         *
         * As an example, `map.findElements('input')` would find all `<input>`
         * nodes while `map.findElements('type', 'text')` would find any DOM node
         * with a `type="text"` attribute.
         *
         * @param {string} selector_or_attrname
         * If invoked with only one parameter, this argument is a
         * `querySelectorAll()` compatible selector expression. If invoked with
         * two parameters, this argument is the attribute name to filter for.
         *
         * @param {string} [attrvalue]
         * In case the function is invoked with two parameters, this argument
         * specifies the attribute value to match.
         *
         * @throws {InternalError}
         * Throws an `InternalError` if more than two function parameters are
         * passed.
         *
         * @returns {NodeList}
         * Returns a (possibly empty) DOM `NodeList` containing the found DOM nodes.
         */
        findElements: function(/* ... */) {
                var q = null;

                if (arguments.length == 1)
                        q = arguments[0];
                else if (arguments.length == 2)
                        q = '[%s="%s"]'.format(arguments[0], arguments[1]);
                else
                        L.error('InternalError', 'Expecting one or two arguments to findElements()');

                return this.root.querySelectorAll(q);
        },

        /**
         * Find the first DOM node within this Map which matches the given search
         * parameters. This function is essentially a convenience wrapper around
         * `findElements()` which only returns the first found node.
         *
         * This function is sensitive to the amount of arguments passed to it;
         * if only one argument is specified, it is used as selector-expression
         * as-is. When two arguments are passed, the first argument is treated
         * as attribute name, the second one as attribute value to match.
         *
         * As an example, `map.findElement('input')` would find the first `<input>`
         * node while `map.findElement('type', 'text')` would find the first DOM
         * node with a `type="text"` attribute.
         *
         * @param {string} selector_or_attrname
         * If invoked with only one parameter, this argument is a `querySelector()`
         * compatible selector expression. If invoked with two parameters, this
         * argument is the attribute name to filter for.
         *
         * @param {string} [attrvalue]
         * In case the function is invoked with two parameters, this argument
         * specifies the attribute value to match.
         *
         * @throws {InternalError}
         * Throws an `InternalError` if more than two function parameters are
         * passed.
         *
         * @returns {Node|null}
         * Returns the first found DOM node or `null` if no element matched.
         */
        findElement: function(/* ... */) {
                var res = this.findElements.apply(this, arguments);
                return res.length ? res[0] : null;
        },

        /**
         * Tie another UCI configuration to the map.
         *
         * By default, a map instance will only load the UCI configuration file
         * specified in the constructor but sometimes access to values from
         * further configuration files is required. This function allows for such
         * use cases by registering further UCI configuration files which are
         * needed by the map.
         *
         * @param {string} config
         * The additional UCI configuration file to tie to the map. If the given
         * config already is in the list of required files, it will be ignored.
         */
        chain: function(config) {
                if (this.parsechain.indexOf(config) == -1)
                        this.parsechain.push(config);
        },

        /**
         * Add a configuration section to the map.
         *
         * LuCI forms follow the structure of the underlying UCI configurations,
         * means that a map, which represents a single UCI configuration, is
         * divided into multiple sections which in turn contain an arbitrary
         * number of options.
         *
         * While UCI itself only knows two kinds of sections - named and anonymous
         * ones - the form class offers various flavors of form section elements
         * to present configuration sections in different ways. Refer to the
         * documentation of the different section classes for details.
         *
         * @param {LuCI.form.AbstractSection} sectionclass
         * The section class to use for rendering the configuration section.
         * Note that this value must be the class itself, not a class instance
         * obtained from calling `new`. It must also be a class dervied from
         * `LuCI.form.AbstractSection`.
         *
         * @param {...string} classargs
         * Additional arguments which are passed as-is to the contructor of the
         * given section class. Refer to the class specific constructor
         * documentation for details.
         *
         * @returns {LuCI.form.AbstractSection}
         * Returns the instantiated section class instance.
         */
        section: function(cbiClass /*, ... */) {
                if (!CBIAbstractSection.isSubclass(cbiClass))
                        L.error('TypeError', 'Class must be a descendent of CBIAbstractSection');

                var obj = cbiClass.instantiate(this.varargs(arguments, 1, this));
                this.append(obj);
                return obj;
        },

        /**
         * Load the configuration covered by this map.
         *
         * The `load()` function first loads all referenced UCI configurations,
         * then it recursively walks the form element tree and invokes the
         * load function of each child element.
         *
         * @returns {Promise<void>}
         * Returns a promise resolving once the entire form completed loading all
         * data. The promise may reject with an error if any configuration failed
         * to load or if any of the child elements load functions rejected with
         * an error.
         */
        load: function() {
                var doCheckACL = (!(this instanceof CBIJSONMap) && this.readonly == null),
                    loadTasks = [ doCheckACL ? callSessionAccess('uci', this.config, 'write') : true ],
                    configs = this.parsechain || [ this.config ];

                loadTasks.push.apply(loadTasks, configs.map(L.bind(function(config, i) {
                        return i ? L.resolveDefault(this.data.load(config)) : this.data.load(config);
                }, this)));

                return Promise.all(loadTasks).then(L.bind(function(res) {
                        if (res[0] === false)
                                this.readonly = true;

                        return this.loadChildren();
                }, this));
        },

        /**
         * Parse the form input values.
         *
         * The `parse()` function recursively walks the form element tree and
         * triggers input value reading and validation for each child element.
         *
         * Elements which are hidden due to unsatisified dependencies are skipped.
         *
         * @returns {Promise<void>}
         * Returns a promise resolving once the entire form completed parsing all
         * input values. The returned promise is rejected if any parsed values are
         * not meeting the validation constraints of their respective elements.
         */
        parse: function() {
                var tasks = [];

                if (Array.isArray(this.children))
                        for (var i = 0; i < this.children.length; i++)
                                tasks.push(this.children[i].parse());

                return Promise.all(tasks);
        },

        /**
         * Save the form input values.
         *
         * This function parses the current form, saves the resulting UCI changes,
         * reloads the UCI configuration data and redraws the form elements.
         *
         * @param {function} [cb]
         * An optional callback function that is invoked after the form is parsed
         * but before the changed UCI data is saved. This is useful to perform
         * additional data manipulation steps before saving the changes.
         *
         * @param {boolean} [silent=false]
         * If set to `true`, trigger an alert message to the user in case saving
         * the form data failes. Otherwise fail silently.
         *
         * @returns {Promise<void>}
         * Returns a promise resolving once the entire save operation is complete.
         * The returned promise is rejected if any step of the save operation
         * failed.
         */
        save: function(cb, silent) {
                this.checkDepends();

                return this.parse()
                        .then(cb)
                        .then(this.data.save.bind(this.data))
                        .then(this.load.bind(this))
                        .catch(function(e) {
                                if (!silent) {
                                        ui.showModal(_('Save error'), [
                                                E('p', {}, [ _('An error occurred while saving the form:') ]),
                                                E('p', {}, [ E('em', { 'style': 'white-space:pre' }, [ e.message ]) ]),
                                                E('div', { 'class': 'right' }, [
                                                        E('button', { 'click': ui.hideModal }, [ _('Dismiss') ])
                                                ])
                                        ]);
                                }

                                return Promise.reject(e);
                        }).then(this.renderContents.bind(this));
        },

        /**
         * Reset the form by re-rendering its contents. This will revert all
         * unsaved user inputs to their initial form state.
         *
         * @returns {Promise<Node>}
         * Returns a promise resolving to the toplevel form DOM node once the
         * re-rendering is complete.
         */
        reset: function() {
                return this.renderContents();
        },

        /**
         * Render the form markup.
         *
         * @returns {Promise<Node>}
         * Returns a promise resolving to the toplevel form DOM node once the
         * rendering is complete.
         */
        render: function() {
                return this.load().then(this.renderContents.bind(this));
        },

        /** @private */
        renderContents: function() {
                var mapEl = this.root || (this.root = E('div', {
                        'id': 'cbi-%s'.format(this.config),
                        'class': 'cbi-map',
                        'cbi-dependency-check': L.bind(this.checkDepends, this)
                }));

                dom.bindClassInstance(mapEl, this);

                return this.renderChildren(null).then(L.bind(function(nodes) {
                        var initialRender = !mapEl.firstChild;

                        dom.content(mapEl, null);

                        if (this.title != null && this.title != '')
                                mapEl.appendChild(E('h2', { 'name': 'content' }, this.title));

                        if (this.description != null && this.description != '')
                                mapEl.appendChild(E('div', { 'class': 'cbi-map-descr' }, this.description));

                        if (this.tabbed)
                                dom.append(mapEl, E('div', { 'class': 'cbi-map-tabbed' }, nodes));
                        else
                                dom.append(mapEl, nodes);

                        if (!initialRender) {
                                mapEl.classList.remove('flash');

                                window.setTimeout(function() {
                                        mapEl.classList.add('flash');
                                }, 1);
                        }

                        this.checkDepends();

                        var tabGroups = mapEl.querySelectorAll('.cbi-map-tabbed, .cbi-section-node-tabbed');

                        for (var i = 0; i < tabGroups.length; i++)
                                ui.tabs.initTabGroup(tabGroups[i].childNodes);

                        return mapEl;
                }, this));
        },

        /**
         * Find a form option element instance.
         *
         * @param {string} name_or_id
         * The name or the full ID of the option element to look up.
         *
         * @param {string} [section_id]
         * The ID of the UCI section containing the option to look up. May be
         * omitted if a full ID is passed as first argument.
         *
         * @param {string} [config]
         * The name of the UCI configuration the option instance is belonging to.
         * Defaults to the main UCI configuration of the map if omitted.
         *
         * @returns {Array<LuCI.form.AbstractValue,string>|null}
         * Returns a two-element array containing the form option instance as
         * first item and the corresponding UCI section ID as second item.
         * Returns `null` if the option could not be found.
         */
        lookupOption: function(name, section_id, config_name) {
                var id, elem, sid, inst;

                if (name.indexOf('.') > -1)
                        id = 'cbid.%s'.format(name);
                else
                        id = 'cbid.%s.%s.%s'.format(config_name || this.config, section_id, name);

                elem = this.findElement('data-field', id);
                sid  = elem ? id.split(/\./)[2] : null;
                inst = elem ? dom.findClassInstance(elem) : null;

                return (inst instanceof CBIAbstractValue) ? [ inst, sid ] : null;
        },

        /** @private */
        checkDepends: function(ev, n) {
                var changed = false;

                for (var i = 0, s = this.children[0]; (s = this.children[i]) != null; i++)
                        if (s.checkDepends(ev, n))
                                changed = true;

                if (changed && (n || 0) < 10)
                        this.checkDepends(ev, (n || 10) + 1);

                ui.tabs.updateTabs(ev, this.root);
        },

        /** @private */
        isDependencySatisfied: function(depends, config_name, section_id) {
                var def = false;

                if (!Array.isArray(depends) || !depends.length)
                        return true;

                for (var i = 0; i < depends.length; i++) {
                        var istat = true,
                            reverse = depends[i]['!reverse'],
                            contains = depends[i]['!contains'];

                        for (var dep in depends[i]) {
                                if (dep == '!reverse' || dep == '!contains') {
                                        continue;
                                }
                                else if (dep == '!default') {
                                        def = true;
                                        istat = false;
                                }
                                else {
                                        var res = this.lookupOption(dep, section_id, config_name),
                                            val = (res && res[0].isActive(res[1])) ? res[0].formvalue(res[1]) : null;

                                        var equal = contains
                                                ? isContained(val, depends[i][dep])
                                                : isEqual(val, depends[i][dep]);

                                        istat = (istat && equal);
                                }
                        }

                        if (istat ^ reverse)
                                return true;
                }

                return def;
        }
});

/**
 * @constructor JSONMap
 * @memberof LuCI.form
 * @augments LuCI.form.Map
 *
 * @classdesc
 *
 * A `JSONMap` class functions similar to [LuCI.form.Map]{@link LuCI.form.Map}
 * but uses a multidimensional JavaScript object instead of UCI configuration
 * as data source.
 *
 * @param {Object<string, Object<string, *>|Array<Object<string, *>>>} data
 * The JavaScript object to use as data source. Internally, the object is
 * converted into an UCI-like format. Its toplevel keys are treated like UCI
 * section types while the object or array-of-object values are treated as
 * section contents.
 *
 * @param {string} [title]
 * The title caption of the form. A form title is usually rendered as separate
 * headline element before the actual form contents. If omitted, the
 * corresponding headline element will not be rendered.
 *
 * @param {string} [description]
 * The description text of the form which is usually rendered as text
 * paragraph below the form title and before the actual form conents.
 * If omitted, the corresponding paragraph element will not be rendered.
 */
var CBIJSONMap = CBIMap.extend(/** @lends LuCI.form.JSONMap.prototype */ {
        __init__: function(data /*, ... */) {
                this.super('__init__', this.varargs(arguments, 1, 'json'));

                this.config = 'json';
                this.parsechain = [ 'json' ];
                this.data = new CBIJSONConfig(data);
        }
});

/**
 * @class AbstractSection
 * @memberof LuCI.form
 * @augments LuCI.form.AbstractElement
 * @hideconstructor
 * @classdesc
 *
 * The `AbstractSection` class serves as abstract base for the different form
 * section styles implemented by `LuCI.form`. It provides the common logic for
 * enumerating underlying configuration section instances, for registering
 * form options and for handling tabs to segment child options.
 *
 * This class is private and not directly accessible by user code.
 */
var CBIAbstractSection = CBIAbstractElement.extend(/** @lends LuCI.form.AbstractSection.prototype */ {
        __init__: function(map, sectionType /*, ... */) {
                this.super('__init__', this.varargs(arguments, 2));

                this.sectiontype = sectionType;
                this.map = map;
                this.config = map.config;

                this.optional = true;
                this.addremove = false;
                this.dynamic = false;
        },

        /**
         * Access the parent option container instance.
         *
         * In case this section is nested within an option element container,
         * this property will hold a reference to the parent option instance.
         *
         * If this section is not nested, the property is `null`.
         *
         * @name LuCI.form.AbstractSection.prototype#parentoption
         * @type LuCI.form.AbstractValue
         * @readonly
         */

        /**
         * Enumerate the UCI section IDs covered by this form section element.
         *
         * @abstract
         * @throws {InternalError}
         * Throws an `InternalError` exception if the function is not implemented.
         *
         * @returns {string[]}
         * Returns an array of UCI section IDs covered by this form element.
         * The sections will be rendered in the same order as the returned array.
         */
        cfgsections: function() {
                L.error('InternalError', 'Not implemented');
        },

        /**
         * Filter UCI section IDs to render.
         *
         * The filter function is invoked for each UCI section ID of a given type
         * and controls whether the given UCI section is rendered or ignored by
         * the form section element.
         *
         * The default implementation always returns `true`. User code or
         * classes extending `AbstractSection` may overwrite this function with
         * custom implementations.
         *
         * @abstract
         * @param {string} section_id
         * The UCI section ID to test.
         *
         * @returns {boolean}
         * Returns `true` when the given UCI section ID should be handled and
         * `false` when it should be ignored.
         */
        filter: function(section_id) {
                return true;
        },

        /**
         * Load the configuration covered by this section.
         *
         * The `load()` function recursively walks the section element tree and
         * invokes the load function of each child option element.
         *
         * @returns {Promise<void>}
         * Returns a promise resolving once the values of all child elements have
         * been loaded. The promise may reject with an error if any of the child
         * elements load functions rejected with an error.
         */
        load: function() {
                var section_ids = this.cfgsections(),
                    tasks = [];

                if (Array.isArray(this.children))
                        for (var i = 0; i < section_ids.length; i++)
                                tasks.push(this.loadChildren(section_ids[i])
                                        .then(Function.prototype.bind.call(function(section_id, set_values) {
                                                for (var i = 0; i < set_values.length; i++)
                                                        this.children[i].cfgvalue(section_id, set_values[i]);
                                        }, this, section_ids[i])));

                return Promise.all(tasks);
        },

        /**
         * Parse this sections form input.
         *
         * The `parse()` function recursively walks the section element tree and
         * triggers input value reading and validation for each encountered child
         * option element.
         *
         * Options which are hidden due to unsatisified dependencies are skipped.
         *
         * @returns {Promise<void>}
         * Returns a promise resolving once the values of all child elements have
         * been parsed. The returned promise is rejected if any parsed values are
         * not meeting the validation constraints of their respective elements.
         */
        parse: function() {
                var section_ids = this.cfgsections(),
                    tasks = [];

                if (Array.isArray(this.children))
                        for (var i = 0; i < section_ids.length; i++)
                                for (var j = 0; j < this.children.length; j++)
                                        tasks.push(this.children[j].parse(section_ids[i]));

                return Promise.all(tasks);
        },

        /**
         * Add an option tab to the section.
         *
         * The child option elements of a section may be divided into multiple
         * tabs to provide a better overview to the user.
         *
         * Before options can be moved into a tab pane, the corresponding tab
         * has to be defined first, which is done by calling this function.
         *
         * Note that once tabs are defined, user code must use the `taboption()`
         * method to add options to specific tabs. Option elements added by
         * `option()` will not be assigned to any tab and not be rendered in this
         * case.
         *
         * @param {string} name
         * The name of the tab to register. It may be freely chosen and just serves
         * as an identifier to differentiate tabs.
         *
         * @param {string} title
         * The human readable caption of the tab.
         *
         * @param {string} [description]
         * An additional description text for the corresponding tab pane. It is
         * displayed as text paragraph below the tab but before the tab pane
         * contents. If omitted, no description will be rendered.
         *
         * @throws {Error}
         * Throws an exeption if a tab with the same `name` already exists.
         */
        tab: function(name, title, description) {
                if (this.tabs && this.tabs[name])
                        throw 'Tab already declared';

                var entry = {
                        name: name,
                        title: title,
                        description: description,
                        children: []
                };

                this.tabs = this.tabs || [];
                this.tabs.push(entry);
                this.tabs[name] = entry;

                this.tab_names = this.tab_names || [];
                this.tab_names.push(name);
        },

        /**
         * Add a configuration option widget to the section.
         *
         * Note that [taboption()]{@link LuCI.form.AbstractSection#taboption}
         * should be used instead if this form section element uses tabs.
         *
         * @param {LuCI.form.AbstractValue} optionclass
         * The option class to use for rendering the configuration option. Note
         * that this value must be the class itself, not a class instance obtained
         * from calling `new`. It must also be a class dervied from
         * [LuCI.form.AbstractSection]{@link LuCI.form.AbstractSection}.
         *
         * @param {...*} classargs
         * Additional arguments which are passed as-is to the contructor of the
         * given option class. Refer to the class specific constructor
         * documentation for details.
         *
         * @throws {TypeError}
         * Throws a `TypeError` exception in case the passed class value is not a
         * descendent of `AbstractValue`.
         *
         * @returns {LuCI.form.AbstractValue}
         * Returns the instantiated option class instance.
         */
        option: function(cbiClass /*, ... */) {
                if (!CBIAbstractValue.isSubclass(cbiClass))
                        throw L.error('TypeError', 'Class must be a descendent of CBIAbstractValue');

                var obj = cbiClass.instantiate(this.varargs(arguments, 1, this.map, this));
                this.append(obj);
                return obj;
        },

        /**
         * Add a configuration option widget to a tab of the section.
         *
         * @param {string} tabname
         * The name of the section tab to add the option element to.
         *
         * @param {LuCI.form.AbstractValue} optionclass
         * The option class to use for rendering the configuration option. Note
         * that this value must be the class itself, not a class instance obtained
         * from calling `new`. It must also be a class dervied from
         * [LuCI.form.AbstractSection]{@link LuCI.form.AbstractSection}.
         *
         * @param {...*} classargs
         * Additional arguments which are passed as-is to the contructor of the
         * given option class. Refer to the class specific constructor
         * documentation for details.
         *
         * @throws {ReferenceError}
         * Throws a `ReferenceError` exception when the given tab name does not
         * exist.
         *
         * @throws {TypeError}
         * Throws a `TypeError` exception in case the passed class value is not a
         * descendent of `AbstractValue`.
         *
         * @returns {LuCI.form.AbstractValue}
         * Returns the instantiated option class instance.
         */
        taboption: function(tabName /*, ... */) {
                if (!this.tabs || !this.tabs[tabName])
                        throw L.error('ReferenceError', 'Associated tab not declared');

                var obj = this.option.apply(this, this.varargs(arguments, 1));
                obj.tab = tabName;
                this.tabs[tabName].children.push(obj);
                return obj;
        },

        /** @private */
        renderUCISection: function(section_id) {
                var renderTasks = [];

                if (!this.tabs)
                        return this.renderOptions(null, section_id);

                for (var i = 0; i < this.tab_names.length; i++)
                        renderTasks.push(this.renderOptions(this.tab_names[i], section_id));

                return Promise.all(renderTasks)
                        .then(this.renderTabContainers.bind(this, section_id));
        },

        /** @private */
        renderTabContainers: function(section_id, nodes) {
                var config_name = this.uciconfig || this.map.config,
                    containerEls = E([]);

                for (var i = 0; i < nodes.length; i++) {
                        var tab_name = this.tab_names[i],
                            tab_data = this.tabs[tab_name],
                            containerEl = E('div', {
                                'id': 'container.%s.%s.%s'.format(config_name, section_id, tab_name),
                                'data-tab': tab_name,
                                'data-tab-title': tab_data.title,
                                'data-tab-active': tab_name === this.selected_tab
                            });

                        if (tab_data.description != null && tab_data.description != '')
                                containerEl.appendChild(
                                        E('div', { 'class': 'cbi-tab-descr' }, tab_data.description));

                        containerEl.appendChild(nodes[i]);
                        containerEls.appendChild(containerEl);
                }

                return containerEls;
        },

        /** @private */
        renderOptions: function(tab_name, section_id) {
                var in_table = (this instanceof CBITableSection);
                return this.renderChildren(tab_name, section_id, in_table).then(function(nodes) {
                        var optionEls = E([]);
                        for (var i = 0; i < nodes.length; i++)
                                optionEls.appendChild(nodes[i]);
                        return optionEls;
                });
        },

        /** @private */
        checkDepends: function(ev, n) {
                var changed = false,
                    sids = this.cfgsections();

                for (var i = 0, sid = sids[0]; (sid = sids[i]) != null; i++) {
                        for (var j = 0, o = this.children[0]; (o = this.children[j]) != null; j++) {
                                var isActive = o.isActive(sid),
                                    isSatisified = o.checkDepends(sid);

                                if (isActive != isSatisified) {
                                        o.setActive(sid, !isActive);
                                        isActive = !isActive;
                                        changed = true;
                                }

                                if (!n && isActive)
                                        o.triggerValidation(sid);
                        }
                }

                return changed;
        }
});


var isEqual = function(x, y) {
        if (x != null && y != null && typeof(x) != typeof(y))
                return false;

        if ((x == null && y != null) || (x != null && y == null))
                return false;

        if (Array.isArray(x)) {
                if (x.length != y.length)
                        return false;

                for (var i = 0; i < x.length; i++)
                        if (!isEqual(x[i], y[i]))
                                return false;
        }
        else if (typeof(x) == 'object') {
                for (var k in x) {
                        if (x.hasOwnProperty(k) && !y.hasOwnProperty(k))
                                return false;

                        if (!isEqual(x[k], y[k]))
                                return false;
                }

                for (var k in y)
                        if (y.hasOwnProperty(k) && !x.hasOwnProperty(k))
                                return false;
        }
        else if (x != y) {
                return false;
        }

        return true;
};

var isContained = function(x, y) {
        if (Array.isArray(x)) {
                for (var i = 0; i < x.length; i++)
                        if (x[i] == y)
                                return true;
        }
        else if (L.isObject(x)) {
                if (x.hasOwnProperty(y) && x[y] != null)
                        return true;
        }
        else if (typeof(x) == 'string') {
                return (x.indexOf(y) > -1);
        }

        return false;
};

/**
 * @class AbstractValue
 * @memberof LuCI.form
 * @augments LuCI.form.AbstractElement
 * @hideconstructor
 * @classdesc
 *
 * The `AbstractValue` class serves as abstract base for the different form
 * option styles implemented by `LuCI.form`. It provides the common logic for
 * handling option input values, for dependencies among options and for
 * validation constraints that should be applied to entered values.
 *
 * This class is private and not directly accessible by user code.
 */
var CBIAbstractValue = CBIAbstractElement.extend(/** @lends LuCI.form.AbstractValue.prototype */ {
        __init__: function(map, section, option /*, ... */) {
                this.super('__init__', this.varargs(arguments, 3));

                this.section = section;
                this.option = option;
                this.map = map;
                this.config = map.config;

                this.deps = [];
                this.initial = {};
                this.rmempty = true;
                this.default = null;
                this.size = null;
                this.optional = false;
        },

        /**
         * If set to `false`, the underlying option value is retained upon saving
         * the form when the option element is disabled due to unsatisfied
         * dependency constraints.
         *
         * @name LuCI.form.AbstractValue.prototype#rmempty
         * @type boolean
         * @default true
         */

        /**
         * If set to `true`, the underlying ui input widget is allowed to be empty,
         * otherwise the option element is marked invalid when no value is entered
         * or selected by the user.
         *
         * @name LuCI.form.AbstractValue.prototype#optional
         * @type boolean
         * @default false
         */

        /**
         * Sets a default value to use when the underlying UCI option is not set.
         *
         * @name LuCI.form.AbstractValue.prototype#default
         * @type *
         * @default null
         */

        /**
         * Specifies a datatype constraint expression to validate input values
         * against. Refer to {@link LuCI.validation} for details on the format.
         *
         * If the user entered input does not match the datatype validation, the
         * option element is marked as invalid.
         *
         * @name LuCI.form.AbstractValue.prototype#datatype
         * @type string
         * @default null
         */

        /**
         * Specifies a custom validation function to test the user input for
         * validity. The validation function must return `true` to accept the
         * value. Any other return value type is converted to a string and
         * displayed to the user as validation error message.
         *
         * If the user entered input does not pass the validation function, the
         * option element is marked as invalid.
         *
         * @name LuCI.form.AbstractValue.prototype#validate
         * @type function
         * @default null
         */

        /**
         * Override the UCI configuration name to read the option value from.
         *
         * By default, the configuration name is inherited from the parent Map.
         * By setting this property, a deviating configuration may be specified.
         *
         * The default is null, means inheriting from the parent form.
         *
         * @name LuCI.form.AbstractValue.prototype#uciconfig
         * @type string
         * @default null
         */

        /**
         * Override the UCI section name to read the option value from.
         *
         * By default, the section ID is inherited from the parent section element.
         * By setting this property, a deviating section may be specified.
         *
         * The default is null, means inheriting from the parent section.
         *
         * @name LuCI.form.AbstractValue.prototype#ucisection
         * @type string
         * @default null
         */

        /**
         * Override the UCI option name to read the value from.
         *
         * By default, the elements name, which is passed as third argument to
         * the constructor, is used as UCI option name. By setting this property,
         * a deviating UCI option may be specified.
         *
         * The default is null, means using the option element name.
         *
         * @name LuCI.form.AbstractValue.prototype#ucioption
         * @type string
         * @default null
         */

        /**
         * Mark grid section option element as editable.
         *
         * Options which are displayed in the table portion of a `GridSection`
         * instance are rendered as readonly text by default. By setting the
         * `editable` property of a child option element to `true`, that element
         * is rendered as full input widget within its cell instead of a text only
         * preview.
         *
         * This property has no effect on options that are not children of grid
         * section elements.
         *
         * @name LuCI.form.AbstractValue.prototype#editable
         * @type boolean
         * @default false
         */

        /**
         * Move grid section option element into the table, the modal popup or both.
         *
         * If this property is `null` (the default), the option element is
         * displayed in both the table preview area and the per-section instance
         * modal popup of a grid section. When it is set to `false` the option
         * is only shown in the table but not the modal popup. When set to `true`,
         * the option is only visible in the modal popup but not the table.
         *
         * This property has no effect on options that are not children of grid
         * section elements.
         *
         * @name LuCI.form.AbstractValue.prototype#modalonly
         * @type boolean
         * @default null
         */

        /**
         * Make option element readonly.
         *
         * This property defaults to the readonly state of the parent form element.
         * When set to `true`, the underlying widget is rendered in disabled state,
         * means its contents cannot be changed and the widget cannot be interacted
         * with.
         *
         * @name LuCI.form.AbstractValue.prototype#readonly
         * @type boolean
         * @default false
         */

        /**
         * Override the cell width of a table or grid section child option.
         *
         * If the property is set to a numeric value, it is treated as pixel width
         * which is set on the containing cell element of the option, essentially
         * forcing a certain column width. When the property is set to a string
         * value, it is applied as-is to the CSS `width` property.
         *
         * This property has no effect on options that are not children of grid or
         * table section elements.
         *
         * @name LuCI.form.AbstractValue.prototype#width
         * @type number|string
         * @default null
         */

        /**
         * Add a dependency contraint to the option.
         *
         * Dependency constraints allow making the presence of option elements
         * dependant on the current values of certain other options within the
         * same form. An option element with unsatisfied dependencies will be
         * hidden from the view and its current value is omitted when saving.
         *
         * Multiple constraints (that is, multiple calls to `depends()`) are
         * treated as alternatives, forming a logical "or" expression.
         *
         * By passing an object of name => value pairs as first argument, it is
         * possible to depend on multiple options simultaneously, allowing to form
         * a logical "and" expression.
         *
         * Option names may be given in "dot notation" which allows to reference
         * option elements outside of the current form section. If a name without
         * dot is specified, it refers to an option within the same configuration
         * section. If specified as <code>configname.sectionid.optionname</code>,
         * options anywhere within the same form may be specified.
         *
         * The object notation also allows for a number of special keys which are
         * not treated as option names but as modifiers to influence the dependency
         * constraint evaluation. The associated value of these special "tag" keys
         * is ignored. The recognized tags are:
         *
         * <ul>
         *   <li>
         *    <code>!reverse</code><br>
         *    Invert the dependency, instead of requiring another option to be
         *    equal to the dependency value, that option should <em>not</em> be
         *    equal.
         *   </li>
         *   <li>
         *    <code>!contains</code><br>
         *    Instead of requiring an exact match, the dependency is considered
         *    satisfied when the dependency value is contained within the option
         *    value.
         *   </li>
         *   <li>
         *    <code>!default</code><br>
         *    The dependency is always satisfied
         *   </li>
         * </ul>
         *
         * Examples:
         *
         * <ul>
         *  <li>
         *   <code>opt.depends("foo", "test")</code><br>
         *   Require the value of `foo` to be `test`.
         *  </li>
         *  <li>
         *   <code>opt.depends({ foo: "test" })</code><br>
         *   Equivalent to the previous example.
         *  </li>
         *  <li>
         *   <code>opt.depends({ foo: "test", bar: "qrx" })</code><br>
         *   Require the value of `foo` to be `test` and the value of `bar` to be
         *   `qrx`.
         *  </li>
         *  <li>
         *   <code>opt.depends({ foo: "test" })<br>
         *         opt.depends({ bar: "qrx" })</code><br>
         *   Require either <code>foo</code> to be set to <code>test</code>,
         *   <em>or</em> the <code>bar</code> option to be <code>qrx</code>.
         *  </li>
         *  <li>
         *   <code>opt.depends("test.section1.foo", "bar")</code><br>
         *   Require the "foo" form option within the "section1" section to be
         *   set to "bar".
         *  </li>
         *  <li>
         *   <code>opt.depends({ foo: "test", "!contains": true })</code><br>
         *   Require the "foo" option value to contain the substring "test".
         *  </li>
         * </ul>
         *
         * @param {string|Object<string, string|boolean>} optionname_or_depends
         * The name of the option to depend on or an object describing multiple
         * dependencies which must be satified (a logical "and" expression).
         *
         * @param {string} optionvalue
         * When invoked with a plain option name as first argument, this parameter
         * specifies the expected value. In case an object is passed as first
         * argument, this parameter is ignored.
         */
        depends: function(field, value) {
                var deps;

                if (typeof(field) === 'string')
                        deps = {}, deps[field] = value;
                else
                        deps = field;

                this.deps.push(deps);
        },

        /** @private */
        transformDepList: function(section_id, deplist) {
                var list = deplist || this.deps,
                    deps = [];

                if (Array.isArray(list)) {
                        for (var i = 0; i < list.length; i++) {
                                var dep = {};

                                for (var k in list[i]) {
                                        if (list[i].hasOwnProperty(k)) {
                                                if (k.charAt(0) === '!')
                                                        dep[k] = list[i][k];
                                                else if (k.indexOf('.') !== -1)
                                                        dep['cbid.%s'.format(k)] = list[i][k];
                                                else
                                                        dep['cbid.%s.%s.%s'.format(
                                                                this.uciconfig || this.section.uciconfig || this.map.config,
                                                                this.ucisection || section_id,
                                                                k
                                                        )] = list[i][k];
                                        }
                                }

                                for (var k in dep) {
                                        if (dep.hasOwnProperty(k)) {
                                                deps.push(dep);
                                                break;
                                        }
                                }
                        }
                }

                return deps;
        },

        /** @private */
        transformChoices: function() {
                if (!Array.isArray(this.keylist) || this.keylist.length == 0)
                        return null;

                var choices = {};

                for (var i = 0; i < this.keylist.length; i++)
                        choices[this.keylist[i]] = this.vallist[i];

                return choices;
        },

        /** @private */
        checkDepends: function(section_id) {
                var config_name = this.uciconfig || this.section.uciconfig || this.map.config,
                    active = this.map.isDependencySatisfied(this.deps, config_name, section_id);

                if (active)
                        this.updateDefaultValue(section_id);

                return active;
        },

        /** @private */
        updateDefaultValue: function(section_id) {
                if (!L.isObject(this.defaults))
                        return;

                var config_name = this.uciconfig || this.section.uciconfig || this.map.config,
                    cfgvalue = L.toArray(this.cfgvalue(section_id))[0],
                    default_defval = null, satisified_defval = null;

                for (var value in this.defaults) {
                        if (!this.defaults[value] || this.defaults[value].length == 0) {
                                default_defval = value;
                                continue;
                        }
                        else if (this.map.isDependencySatisfied(this.defaults[value], config_name, section_id)) {
                                satisified_defval = value;
                                break;
                        }
                }

                if (satisified_defval == null)
                        satisified_defval = default_defval;

                var node = this.map.findElement('id', this.cbid(section_id));
                if (node && node.getAttribute('data-changed') != 'true' && satisified_defval != null && cfgvalue == null)
                        dom.callClassMethod(node, 'setValue', satisified_defval);

                this.default = satisified_defval;
        },

        /**
         * Obtain the internal ID ("cbid") of the element instance.
         *
         * Since each form section element may map multiple underlying
         * configuration sections, the configuration section ID is required to
         * form a fully qualified ID pointing to the specific element instance
         * within the given specific section.
         *
         * @param {string} section_id
         * The configuration section ID
         *
         * @throws {TypeError}
         * Throws a `TypeError` exception when no `section_id` was specified.
         *
         * @returns {string}
         * Returns the element ID.
         */
        cbid: function(section_id) {
                if (section_id == null)
                        L.error('TypeError', 'Section ID required');

                return 'cbid.%s.%s.%s'.format(
                        this.uciconfig || this.section.uciconfig || this.map.config,
                        section_id, this.option);
        },

        /**
         * Load the underlying configuration value.
         *
         * The default implementation of this method reads and returns the
         * underlying UCI option value (or the related JavaScript property for
         * `JSONMap` instances). It may be overwritten by user code to load data
         * from nonstandard sources.
         *
         * @param {string} section_id
         * The configuration section ID
         *
         * @throws {TypeError}
         * Throws a `TypeError` exception when no `section_id` was specified.
         *
         * @returns {*|Promise<*>}
         * Returns the configuration value to initialize the option element with.
         * The return value of this function is filtered through `Promise.resolve()`
         * so it may return promises if overridden by user code.
         */
        load: function(section_id) {
                if (section_id == null)
                        L.error('TypeError', 'Section ID required');

                return this.map.data.get(
                        this.uciconfig || this.section.uciconfig || this.map.config,
                        this.ucisection || section_id,
                        this.ucioption || this.option);
        },

        /**
         * Obtain the underlying `LuCI.ui` element instance.
         *
         * @param {string} section_id
         * The configuration section ID
         *
         * @throws {TypeError}
         * Throws a `TypeError` exception when no `section_id` was specified.
         *
         * @return {LuCI.ui.AbstractElement|null}
         * Returns the `LuCI.ui` element instance or `null` in case the form
         * option implementation does not use `LuCI.ui` widgets.
         */
        getUIElement: function(section_id) {
                var node = this.map.findElement('id', this.cbid(section_id)),
                    inst = node ? dom.findClassInstance(node) : null;
                return (inst instanceof ui.AbstractElement) ? inst : null;
        },

        /**
         * Query the underlying configuration value.
         *
         * The default implementation of this method returns the cached return
         * value of [load()]{@link LuCI.form.AbstractValue#load}. It may be
         * overwritten by user code to obtain the configuration value in a
         * different way.
         *
         * @param {string} section_id
         * The configuration section ID
         *
         * @throws {TypeError}
         * Throws a `TypeError` exception when no `section_id` was specified.
         *
         * @returns {*}
         * Returns the configuration value.
         */
        cfgvalue: function(section_id, set_value) {
                if (section_id == null)
                        L.error('TypeError', 'Section ID required');

                if (arguments.length == 2) {
                        this.data = this.data || {};
                        this.data[section_id] = set_value;
                }

                return this.data ? this.data[section_id] : null;
        },

        /**
         * Query the current form input value.
         *
         * The default implementation of this method returns the current input
         * value of the underlying [LuCI.ui]{@link LuCI.ui.AbstractElement} widget.
         * It may be overwritten by user code to handle input values differently.
         *
         * @param {string} section_id
         * The configuration section ID
         *
         * @throws {TypeError}
         * Throws a `TypeError` exception when no `section_id` was specified.
         *
         * @returns {*}
         * Returns the current input value.
         */
        formvalue: function(section_id) {
                var elem = this.getUIElement(section_id);
                return elem ? elem.getValue() : null;
        },

        /**
         * Obtain a textual input representation.
         *
         * The default implementation of this method returns the HTML escaped
         * current input value of the underlying
         * [LuCI.ui]{@link LuCI.ui.AbstractElement} widget. User code or specific
         * option element implementations may overwrite this function to apply a
         * different logic, e.g. to return `Yes` or `No` depending on the checked
         * state of checkbox elements.
         *
         * @param {string} section_id
         * The configuration section ID
         *
         * @throws {TypeError}
         * Throws a `TypeError` exception when no `section_id` was specified.
         *
         * @returns {string}
         * Returns the text representation of the current input value.
         */
        textvalue: function(section_id) {
                var cval = this.cfgvalue(section_id);

                if (cval == null)
                        cval = this.default;

                return (cval != null) ? '%h'.format(cval) : null;
        },

        /**
         * Apply custom validation logic.
         *
         * This method is invoked whenever incremental validation is performed on
         * the user input, e.g. on keyup or blur events.
         *
         * The default implementation of this method does nothing and always
         * returns `true`. User code may overwrite this method to provide
         * additional validation logic which is not covered by data type
         * constraints.
         *
         * @abstract
         * @param {string} section_id
         * The configuration section ID
         *
         * @param {*} value
         * The value to validate
         *
         * @returns {*}
         * The method shall return `true` to accept the given value. Any other
         * return value is treated as failure, converted to a string and displayed
         * as error message to the user.
         */
        validate: function(section_id, value) {
                return true;
        },

        /**
         * Test whether the input value is currently valid.
         *
         * @param {string} section_id
         * The configuration section ID
         *
         * @returns {boolean}
         * Returns `true` if the input value currently is valid, otherwise it
         * returns `false`.
         */
        isValid: function(section_id) {
                var elem = this.getUIElement(section_id);
                return elem ? elem.isValid() : true;
        },

        /**
         * Test whether the option element is currently active.
         *
         * An element is active when it is not hidden due to unsatisfied dependency
         * constraints.
         *
         * @param {string} section_id
         * The configuration section ID
         *
         * @returns {boolean}
         * Returns `true` if the option element currently is active, otherwise it
         * returns `false`.
         */
        isActive: function(section_id) {
                var field = this.map.findElement('data-field', this.cbid(section_id));
                return (field != null && !field.classList.contains('hidden'));
        },

        /** @private */
        setActive: function(section_id, active) {
                var field = this.map.findElement('data-field', this.cbid(section_id));

                if (field && field.classList.contains('hidden') == active) {
                        field.classList[active ? 'remove' : 'add']('hidden');
                        return true;
                }

                return false;
        },

        /** @private */
        triggerValidation: function(section_id) {
                var elem = this.getUIElement(section_id);
                return elem ? elem.triggerValidation() : true;
        },

        /**
         * Parse the option element input.
         *
         * The function is invoked when the `parse()` method has been invoked on
         * the parent form and triggers input value reading and validation.
         *
         * @param {string} section_id
         * The configuration section ID
         *
         * @returns {Promise<void>}
         * Returns a promise resolving once the input value has been read and
         * validated or rejecting in case the input value does not meet the
         * validation constraints.
         */
        parse: function(section_id) {
                var active = this.isActive(section_id),
                    cval = this.cfgvalue(section_id),
                    fval = active ? this.formvalue(section_id) : null;

                if (active && !this.isValid(section_id)) {
                        var title = this.stripTags(this.title).trim();
                        return Promise.reject(new TypeError(_('Option "%s" contains an invalid input value.').format(title || this.option)));
                }

                if (fval != '' && fval != null) {
                        if (this.forcewrite || !isEqual(cval, fval))
                                return Promise.resolve(this.write(section_id, fval));
                }
                else {
                        if (!active || this.rmempty || this.optional) {
                                return Promise.resolve(this.remove(section_id));
                        }
                        else if (!isEqual(cval, fval)) {
                                var title = this.stripTags(this.title).trim();
                                return Promise.reject(new TypeError(_('Option "%s" must not be empty.').format(title || this.option)));
                        }
                }

                return Promise.resolve();
        },

        /**
         * Write the current input value into the configuration.
         *
         * This function is invoked upon saving the parent form when the option
         * element is valid and when its input value has been changed compared to
         * the initial value returned by
         * [cfgvalue()]{@link LuCI.form.AbstractValue#cfgvalue}.
         *
         * The default implementation simply sets the given input value in the
         * UCI configuration (or the associated JavaScript object property in
         * case of `JSONMap` forms). It may be overwritten by user code to
         * implement alternative save logic, e.g. to transform the input value
         * before it is written.
         *
         * @param {string} section_id
         * The configuration section ID
         *
         * @param {string|string[]}     formvalue
         * The input value to write.
         */
        write: function(section_id, formvalue) {
                return this.map.data.set(
                        this.uciconfig || this.section.uciconfig || this.map.config,
                        this.ucisection || section_id,
                        this.ucioption || this.option,
                        formvalue);
        },

        /**
         * Remove the corresponding value from the configuration.
         *
         * This function is invoked upon saving the parent form when the option
         * element has been hidden due to unsatisfied dependencies or when the
         * user cleared the input value and the option is marked optional.
         *
         * The default implementation simply removes the associated option from the
         * UCI configuration (or the associated JavaScript object property in
         * case of `JSONMap` forms). It may be overwritten by user code to
         * implement alternative removal logic, e.g. to retain the original value.
         *
         * @param {string} section_id
         * The configuration section ID
         */
        remove: function(section_id) {
                return this.map.data.unset(
                        this.uciconfig || this.section.uciconfig || this.map.config,
                        this.ucisection || section_id,
                        this.ucioption || this.option);
        }
});

/**
 * @class TypedSection
 * @memberof LuCI.form
 * @augments LuCI.form.AbstractSection
 * @hideconstructor
 * @classdesc
 *
 * The `TypedSection` class maps all or - if `filter()` is overwritten - a
 * subset of the underlying UCI configuration sections of a given type.
 *
 * Layout wise, the configuration section instances mapped by the section
 * element (sometimes referred to as "section nodes") are stacked beneath
 * each other in a single column, with an optional section remove button next
 * to each section node and a section add button at the end, depending on the
 * value of the `addremove` property.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [section()]{@link LuCI.form.Map#section}.
 *
 * @param {string} section_type
 * The type of the UCI section to map.
 *
 * @param {string} [title]
 * The title caption of the form section element.
 *
 * @param {string} [description]
 * The description text of the form section element.
 */
var CBITypedSection = CBIAbstractSection.extend(/** @lends LuCI.form.TypedSection.prototype */ {
        __name__: 'CBI.TypedSection',

        /**
         * If set to `true`, the user may add or remove instances from the form
         * section widget, otherwise only preexisting sections may be edited.
         * The default is `false`.
         *
         * @name LuCI.form.TypedSection.prototype#addremove
         * @type boolean
         * @default false
         */

        /**
         * If set to `true`, mapped section instances are treated as anonymous
         * UCI sections, which means that section instance elements will be
         * rendered without title element and that no name is required when adding
         * new sections. The default is `false`.
         *
         * @name LuCI.form.TypedSection.prototype#anonymous
         * @type boolean
         * @default false
         */

        /**
         * When set to `true`, instead of rendering section instances one below
         * another, treat each instance as separate tab pane and render a tab menu
         * at the top of the form section element, allowing the user to switch
         * among instances. The default is `false`.
         *
         * @name LuCI.form.TypedSection.prototype#tabbed
         * @type boolean
         * @default false
         */

        /**
         * Override the caption used for the section add button at the bottom of
         * the section form element. If set to a string, it will be used as-is,
         * if set to a function, the function will be invoked and its return value
         * is used as caption, after converting it to a string. If this property
         * is not set, the default is `Add`.
         *
         * @name LuCI.form.TypedSection.prototype#addbtntitle
         * @type string|function
         * @default null
         */

        /**
         * Override the UCI configuration name to read the section IDs from. By
         * default, the configuration name is inherited from the parent `Map`.
         * By setting this property, a deviating configuration may be specified.
         * The default is `null`, means inheriting from the parent form.
         *
         * @name LuCI.form.TypedSection.prototype#uciconfig
         * @type string
         * @default null
         */

        /** @override */
        cfgsections: function() {
                return this.map.data.sections(this.uciconfig || this.map.config, this.sectiontype)
                        .map(function(s) { return s['.name'] })
                        .filter(L.bind(this.filter, this));
        },

        /** @private */
        handleAdd: function(ev, name) {
                var config_name = this.uciconfig || this.map.config;

                this.map.data.add(config_name, this.sectiontype, name);
                return this.map.save(null, true);
        },

        /** @private */
        handleRemove: function(section_id, ev) {
                var config_name = this.uciconfig || this.map.config;

                this.map.data.remove(config_name, section_id);
                return this.map.save(null, true);
        },

        /** @private */
        renderSectionAdd: function(extra_class) {
                if (!this.addremove)
                        return E([]);

                var createEl = E('div', { 'class': 'cbi-section-create' }),
                    config_name = this.uciconfig || this.map.config,
                    btn_title = this.titleFn('addbtntitle');

                if (extra_class != null)
                        createEl.classList.add(extra_class);

                if (this.anonymous) {
                        createEl.appendChild(E('button', {
                                'class': 'cbi-button cbi-button-add',
                                'title': btn_title || _('Add'),
                                'click': ui.createHandlerFn(this, 'handleAdd'),
                                'disabled': this.map.readonly || null
                        }, [ btn_title || _('Add') ]));
                }
                else {
                        var nameEl = E('input', {
                                'type': 'text',
                                'class': 'cbi-section-create-name',
                                'disabled': this.map.readonly || null
                        });

                        dom.append(createEl, [
                                E('div', {}, nameEl),
                                E('input', {
                                        'class': 'cbi-button cbi-button-add',
                                        'type': 'submit',
                                        'value': btn_title || _('Add'),
                                        'title': btn_title || _('Add'),
                                        'click': ui.createHandlerFn(this, function(ev) {
                                                if (nameEl.classList.contains('cbi-input-invalid'))
                                                        return;

                                                return this.handleAdd(ev, nameEl.value);
                                        }),
                                        'disabled': this.map.readonly || null
                                })
                        ]);

                        ui.addValidator(nameEl, 'uciname', true, 'blur', 'keyup');
                }

                return createEl;
        },

        /** @private */
        renderSectionPlaceholder: function() {
                return E([
                        E('em', _('This section contains no values yet')),
                        E('br'), E('br')
                ]);
        },

        /** @private */
        renderContents: function(cfgsections, nodes) {
                var section_id = null,
                    config_name = this.uciconfig || this.map.config,
                    sectionEl = E('div', {
                                'id': 'cbi-%s-%s'.format(config_name, this.sectiontype),
                                'class': 'cbi-section',
                                'data-tab': (this.map.tabbed && !this.parentoption) ? this.sectiontype : null,
                                'data-tab-title': (this.map.tabbed && !this.parentoption) ? this.title || this.sectiontype : null
                        });

                if (this.title != null && this.title != '')
                        sectionEl.appendChild(E('legend', {}, this.title));

                if (this.description != null && this.description != '')
                        sectionEl.appendChild(E('div', { 'class': 'cbi-section-descr' }, this.description));

                for (var i = 0; i < nodes.length; i++) {
                        if (this.addremove) {
                                sectionEl.appendChild(
                                        E('div', { 'class': 'cbi-section-remove right' },
                                                E('button', {
                                                        'class': 'cbi-button',
                                                        'name': 'cbi.rts.%s.%s'.format(config_name, cfgsections[i]),
                                                        'data-section-id': cfgsections[i],
                                                        'click': ui.createHandlerFn(this, 'handleRemove', cfgsections[i]),
                                                        'disabled': this.map.readonly || null
                                                }, [ _('Delete') ])));
                        }

                        if (!this.anonymous)
                                sectionEl.appendChild(E('h3', cfgsections[i].toUpperCase()));

                        sectionEl.appendChild(E('div', {
                                'id': 'cbi-%s-%s'.format(config_name, cfgsections[i]),
                                'class': this.tabs
                                        ? 'cbi-section-node cbi-section-node-tabbed' : 'cbi-section-node',
                                'data-section-id': cfgsections[i]
                        }, nodes[i]));
                }

                if (nodes.length == 0)
                        sectionEl.appendChild(this.renderSectionPlaceholder());

                sectionEl.appendChild(this.renderSectionAdd());

                dom.bindClassInstance(sectionEl, this);

                return sectionEl;
        },

        /** @override */
        render: function() {
                var cfgsections = this.cfgsections(),
                    renderTasks = [];

                for (var i = 0; i < cfgsections.length; i++)
                        renderTasks.push(this.renderUCISection(cfgsections[i]));

                return Promise.all(renderTasks).then(this.renderContents.bind(this, cfgsections));
        }
});

/**
 * @class TableSection
 * @memberof LuCI.form
 * @augments LuCI.form.TypedSection
 * @hideconstructor
 * @classdesc
 *
 * The `TableSection` class maps all or - if `filter()` is overwritten - a
 * subset of the underlying UCI configuration sections of a given type.
 *
 * Layout wise, the configuration section instances mapped by the section
 * element (sometimes referred to as "section nodes") are rendered as rows
 * within an HTML table element, with an optional section remove button in the
 * last column and a section add button below the table, depending on the
 * value of the `addremove` property.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [section()]{@link LuCI.form.Map#section}.
 *
 * @param {string} section_type
 * The type of the UCI section to map.
 *
 * @param {string} [title]
 * The title caption of the form section element.
 *
 * @param {string} [description]
 * The description text of the form section element.
 */
var CBITableSection = CBITypedSection.extend(/** @lends LuCI.form.TableSection.prototype */ {
        __name__: 'CBI.TableSection',

        /**
         * If set to `true`, the user may add or remove instances from the form
         * section widget, otherwise only preexisting sections may be edited.
         * The default is `false`.
         *
         * @name LuCI.form.TableSection.prototype#addremove
         * @type boolean
         * @default false
         */

        /**
         * If set to `true`, mapped section instances are treated as anonymous
         * UCI sections, which means that section instance elements will be
         * rendered without title element and that no name is required when adding
         * new sections. The default is `false`.
         *
         * @name LuCI.form.TableSection.prototype#anonymous
         * @type boolean
         * @default false
         */

        /**
         * Override the caption used for the section add button at the bottom of
         * the section form element. If set to a string, it will be used as-is,
         * if set to a function, the function will be invoked and its return value
         * is used as caption, after converting it to a string. If this property
         * is not set, the default is `Add`.
         *
         * @name LuCI.form.TableSection.prototype#addbtntitle
         * @type string|function
         * @default null
         */

        /**
         * Override the per-section instance title caption shown in the first
         * column of the table unless `anonymous` is set to true. If set to a
         * string, it will be used as `String.format()` pattern with the name of
         * the underlying UCI section as first argument, if set to a function, the
         * function will be invoked with the section name as first argument and
         * its return value is used as caption, after converting it to a string.
         * If this property is not set, the default is the name of the underlying
         * UCI configuration section.
         *
         * @name LuCI.form.TableSection.prototype#sectiontitle
         * @type string|function
         * @default null
         */

        /**
         * Override the per-section instance modal popup title caption shown when
         * clicking the `More…` button in a section specifying `max_cols`. If set
         * to a string, it will be used as `String.format()` pattern with the name
         * of the underlying UCI section as first argument, if set to a function,
         * the function will be invoked with the section name as first argument and
         * its return value is used as caption, after converting it to a string.
         * If this property is not set, the default is the name of the underlying
         * UCI configuration section.
         *
         * @name LuCI.form.TableSection.prototype#modaltitle
         * @type string|function
         * @default null
         */

        /**
         * Override the UCI configuration name to read the section IDs from. By
         * default, the configuration name is inherited from the parent `Map`.
         * By setting this property, a deviating configuration may be specified.
         * The default is `null`, means inheriting from the parent form.
         *
         * @name LuCI.form.TableSection.prototype#uciconfig
         * @type string
         * @default null
         */

        /**
         * Specify a maximum amount of columns to display. By default, one table
         * column is rendered for each child option of the form section element.
         * When this option is set to a positive number, then no more columns than
         * the given amount are rendered. When the number of child options exceeds
         * the specified amount, a `More…` button is rendered in the last column,
         * opening a modal dialog presenting all options elements in `NamedSection`
         * style when clicked.
         *
         * @name LuCI.form.TableSection.prototype#max_cols
         * @type number
         * @default null
         */

        /**
         * If set to `true`, alternating `cbi-rowstyle-1` and `cbi-rowstyle-2` CSS
         * classes are added to the table row elements. Not all LuCI themes
         * implement these row style classes. The default is `false`.
         *
         * @name LuCI.form.TableSection.prototype#rowcolors
         * @type boolean
         * @default false
         */

        /**
         * Enables a per-section instance row `Edit` button which triggers a certain
         * action when clicked. If set to a string, the string value is used
         * as `String.format()` pattern with the name of the underlying UCI section
         * as first format argument. The result is then interpreted as URL which
         * LuCI will navigate to when the user clicks the edit button.
         *
         * If set to a function, this function will be registered as click event
         * handler on the rendered edit button, receiving the section instance
         * name as first and the DOM click event as second argument.
         *
         * @name LuCI.form.TableSection.prototype#extedit
         * @type string|function
         * @default null
         */

        /**
         * If set to `true`, a sort button is added to the last column, allowing
         * the user to reorder the section instances mapped by the section form
         * element.
         *
         * @name LuCI.form.TableSection.prototype#sortable
         * @type boolean
         * @default false
         */

        /**
         * If set to `true`, the header row with the options descriptions will
         * not be displayed. By default, descriptions row is automatically displayed
         * when at least one option has a description.
         *
         * @name LuCI.form.TableSection.prototype#nodescriptions
         * @type boolean
         * @default false
         */

        /**
         * The `TableSection` implementation does not support option tabbing, so
         * its implementation of `tab()` will always throw an exception when
         * invoked.
         *
         * @override
         * @throws Throws an exception when invoked.
         */
        tab: function() {
                throw 'Tabs are not supported by TableSection';
        },

        /** @private */
        renderContents: function(cfgsections, nodes) {
                var section_id = null,
                    config_name = this.uciconfig || this.map.config,
                    max_cols = isNaN(this.max_cols) ? this.children.length : this.max_cols,
                    has_more = max_cols < this.children.length,
                    sectionEl = E('div', {
                                'id': 'cbi-%s-%s'.format(config_name, this.sectiontype),
                                'class': 'cbi-section cbi-tblsection',
                                'data-tab': (this.map.tabbed && !this.parentoption) ? this.sectiontype : null,
                                'data-tab-title': (this.map.tabbed && !this.parentoption) ? this.title || this.sectiontype : null
                        }),
                        tableEl = E('div', {
                                'class': 'table cbi-section-table'
                        });

                if (this.title != null && this.title != '')
                        sectionEl.appendChild(E('h3', {}, this.title));

                if (this.description != null && this.description != '')
                        sectionEl.appendChild(E('div', { 'class': 'cbi-section-descr' }, this.description));

                tableEl.appendChild(this.renderHeaderRows(max_cols));

                for (var i = 0; i < nodes.length; i++) {
                        var sectionname = this.titleFn('sectiontitle', cfgsections[i]);

                        if (sectionname == null)
                                sectionname = cfgsections[i];

                        var trEl = E('div', {
                                'id': 'cbi-%s-%s'.format(config_name, cfgsections[i]),
                                'class': 'tr cbi-section-table-row',
                                'data-sid': cfgsections[i],
                                'draggable': this.sortable ? true : null,
                                'mousedown': this.sortable ? L.bind(this.handleDragInit, this) : null,
                                'dragstart': this.sortable ? L.bind(this.handleDragStart, this) : null,
                                'dragover': this.sortable ? L.bind(this.handleDragOver, this) : null,
                                'dragenter': this.sortable ? L.bind(this.handleDragEnter, this) : null,
                                'dragleave': this.sortable ? L.bind(this.handleDragLeave, this) : null,
                                'dragend': this.sortable ? L.bind(this.handleDragEnd, this) : null,
                                'drop': this.sortable ? L.bind(this.handleDrop, this) : null,
                                'data-title': (sectionname && (!this.anonymous || this.sectiontitle)) ? sectionname : null,
                                'data-section-id': cfgsections[i]
                        });

                        if (this.extedit || this.rowcolors)
                                trEl.classList.add(!(tableEl.childNodes.length % 2)
                                        ? 'cbi-rowstyle-1' : 'cbi-rowstyle-2');

                        for (var j = 0; j < max_cols && nodes[i].firstChild; j++)
                                trEl.appendChild(nodes[i].firstChild);

                        trEl.appendChild(this.renderRowActions(cfgsections[i], has_more ? _('More…') : null));
                        tableEl.appendChild(trEl);
                }

                if (nodes.length == 0)
                        tableEl.appendChild(E('div', { 'class': 'tr cbi-section-table-row placeholder' },
                                E('div', { 'class': 'td' },
                                        E('em', {}, _('This section contains no values yet')))));

                sectionEl.appendChild(tableEl);

                sectionEl.appendChild(this.renderSectionAdd('cbi-tblsection-create'));

                dom.bindClassInstance(sectionEl, this);

                return sectionEl;
        },

        /** @private */
        renderHeaderRows: function(max_cols, has_action) {
                var has_titles = false,
                    has_descriptions = false,
                    max_cols = isNaN(this.max_cols) ? this.children.length : this.max_cols,
                    has_more = max_cols < this.children.length,
                    anon_class = (!this.anonymous || this.sectiontitle) ? 'named' : 'anonymous',
                    trEls = E([]);

                for (var i = 0, opt; i < max_cols && (opt = this.children[i]) != null; i++) {
                        if (opt.modalonly)
                                continue;

                        has_titles = has_titles || !!opt.title;
                        has_descriptions = has_descriptions || !!opt.description;
                }

                if (has_titles) {
                        var trEl = E('div', {
                                'class': 'tr cbi-section-table-titles ' + anon_class,
                                'data-title': (!this.anonymous || this.sectiontitle) ? _('Name') : null
                        });

                        for (var i = 0, opt; i < max_cols && (opt = this.children[i]) != null; i++) {
                                if (opt.modalonly)
                                        continue;

                                trEl.appendChild(E('div', {
                                        'class': 'th cbi-section-table-cell',
                                        'data-widget': opt.__name__
                                }));

                                if (opt.width != null)
                                        trEl.lastElementChild.style.width =
                                                (typeof(opt.width) == 'number') ? opt.width+'px' : opt.width;

                                if (opt.titleref)
                                        trEl.lastElementChild.appendChild(E('a', {
                                                'href': opt.titleref,
                                                'class': 'cbi-title-ref',
                                                'title': this.titledesc || _('Go to relevant configuration page')
                                        }, opt.title));
                                else
                                        dom.content(trEl.lastElementChild, opt.title);
                        }

                        if (this.sortable || this.extedit || this.addremove || has_more || has_action)
                                trEl.appendChild(E('div', {
                                        'class': 'th cbi-section-table-cell cbi-section-actions'
                                }));

                        trEls.appendChild(trEl);
                }

                if (has_descriptions && !this.nodescriptions) {
                        var trEl = E('div', {
                                'class': 'tr cbi-section-table-descr ' + anon_class
                        });

                        for (var i = 0, opt; i < max_cols && (opt = this.children[i]) != null; i++) {
                                if (opt.modalonly)
                                        continue;

                                trEl.appendChild(E('div', {
                                        'class': 'th cbi-section-table-cell',
                                        'data-widget': opt.__name__
                                }, opt.description));

                                if (opt.width != null)
                                        trEl.lastElementChild.style.width =
                                                (typeof(opt.width) == 'number') ? opt.width+'px' : opt.width;
                        }

                        if (this.sortable || this.extedit || this.addremove || has_more || has_action)
                                trEl.appendChild(E('div', {
                                        'class': 'th cbi-section-table-cell cbi-section-actions'
                                }));

                        trEls.appendChild(trEl);
                }

                return trEls;
        },

        /** @private */
        renderRowActions: function(section_id, more_label) {
                var config_name = this.uciconfig || this.map.config;

                if (!this.sortable && !this.extedit && !this.addremove && !more_label)
                        return E([]);

                var tdEl = E('div', {
                        'class': 'td cbi-section-table-cell nowrap cbi-section-actions'
                }, E('div'));

                if (this.sortable) {
                        dom.append(tdEl.lastElementChild, [
                                E('div', {
                                        'title': _('Drag to reorder'),
                                        'class': 'btn cbi-button drag-handle center',
                                        'style': 'cursor:move',
                                        'disabled': this.map.readonly || null
                                }, '☰')
                        ]);
                }

                if (this.extedit) {
                        var evFn = null;

                        if (typeof(this.extedit) == 'function')
                                evFn = L.bind(this.extedit, this);
                        else if (typeof(this.extedit) == 'string')
                                evFn = L.bind(function(sid, ev) {
                                        location.href = this.extedit.format(sid);
                                }, this, section_id);

                        dom.append(tdEl.lastElementChild,
                                E('button', {
                                        'title': _('Edit'),
                                        'class': 'cbi-button cbi-button-edit',
                                        'click': evFn
                                }, [ _('Edit') ])
                        );
                }

                if (more_label) {
                        dom.append(tdEl.lastElementChild,
                                E('button', {
                                        'title': more_label,
                                        'class': 'cbi-button cbi-button-edit',
                                        'click': ui.createHandlerFn(this, 'renderMoreOptionsModal', section_id)
                                }, [ more_label ])
                        );
                }

                if (this.addremove) {
                        var btn_title = this.titleFn('removebtntitle', section_id);

                        dom.append(tdEl.lastElementChild,
                                E('button', {
                                        'title': btn_title || _('Delete'),
                                        'class': 'cbi-button cbi-button-remove',
                                        'click': ui.createHandlerFn(this, 'handleRemove', section_id),
                                        'disabled': this.map.readonly || null
                                }, [ btn_title || _('Delete') ])
                        );
                }

                return tdEl;
        },

        /** @private */
        handleDragInit: function(ev) {
                scope.dragState = { node: ev.target };
        },

        /** @private */
        handleDragStart: function(ev) {
                if (!scope.dragState || !scope.dragState.node.classList.contains('drag-handle')) {
                        scope.dragState = null;
                        ev.preventDefault();
                        return false;
                }

                scope.dragState.node = dom.parent(scope.dragState.node, '.tr');
                ev.dataTransfer.setData('text', 'drag');
                ev.target.style.opacity = 0.4;
        },

        /** @private */
        handleDragOver: function(ev) {
                var n = scope.dragState.targetNode,
                    r = scope.dragState.rect,
                    t = r.top + r.height / 2;

                if (ev.clientY <= t) {
                        n.classList.remove('drag-over-below');
                        n.classList.add('drag-over-above');
                }
                else {
                        n.classList.remove('drag-over-above');
                        n.classList.add('drag-over-below');
                }

                ev.dataTransfer.dropEffect = 'move';
                ev.preventDefault();
                return false;
        },

        /** @private */
        handleDragEnter: function(ev) {
                scope.dragState.rect = ev.currentTarget.getBoundingClientRect();
                scope.dragState.targetNode = ev.currentTarget;
        },

        /** @private */
        handleDragLeave: function(ev) {
                ev.currentTarget.classList.remove('drag-over-above');
                ev.currentTarget.classList.remove('drag-over-below');
        },

        /** @private */
        handleDragEnd: function(ev) {
                var n = ev.target;

                n.style.opacity = '';
                n.classList.add('flash');
                n.parentNode.querySelectorAll('.drag-over-above, .drag-over-below')
                        .forEach(function(tr) {
                                tr.classList.remove('drag-over-above');
                                tr.classList.remove('drag-over-below');
                        });
        },

        /** @private */
        handleDrop: function(ev) {
                var s = scope.dragState;

                if (s.node && s.targetNode) {
                        var config_name = this.uciconfig || this.map.config,
                            ref_node = s.targetNode,
                            after = false;

                    if (ref_node.classList.contains('drag-over-below')) {
                        ref_node = ref_node.nextElementSibling;
                        after = true;
                    }

                    var sid1 = s.node.getAttribute('data-sid'),
                        sid2 = s.targetNode.getAttribute('data-sid');

                    s.node.parentNode.insertBefore(s.node, ref_node);
                    this.map.data.move(config_name, sid1, sid2, after);
                }

                scope.dragState = null;
                ev.target.style.opacity = '';
                ev.stopPropagation();
                ev.preventDefault();
                return false;
        },

        /** @private */
        handleModalCancel: function(modalMap, ev) {
                return Promise.resolve(ui.hideModal());
        },

        /** @private */
        handleModalSave: function(modalMap, ev) {
                return modalMap.save()
                        .then(L.bind(this.map.load, this.map))
                        .then(L.bind(this.map.reset, this.map))
                        .then(ui.hideModal)
                        .catch(function() {});
        },

        /**
         * Add further options to the per-section instanced modal popup.
         *
         * This function may be overwritten by user code to perform additional
         * setup steps before displaying the more options modal which is useful to
         * e.g. query additional data or to inject further option elements.
         *
         * The default implementation of this function does nothing.
         *
         * @abstract
         * @param {LuCI.form.NamedSection} modalSection
         * The `NamedSection` instance about to be rendered in the modal popup.
         *
         * @param {string} section_id
         * The ID of the underlying UCI section the modal popup belongs to.
         *
         * @param {Event} ev
         * The DOM event emitted by clicking the `More…` button.
         *
         * @returns {*|Promise<*>}
         * Return values of this function are ignored but if a promise is returned,
         * it is run to completion before the rendering is continued, allowing
         * custom logic to perform asynchroneous work before the modal dialog
         * is shown.
         */
        addModalOptions: function(modalSection, section_id, ev) {

        },

        /** @private */
        renderMoreOptionsModal: function(section_id, ev) {
                var parent = this.map,
                    title = parent.title,
                    name = null,
                    m = new CBIMap(this.map.config, null, null),
                    s = m.section(CBINamedSection, section_id, this.sectiontype);

                m.parent = parent;
                m.readonly = parent.readonly;

                s.tabs = this.tabs;
                s.tab_names = this.tab_names;

                if ((name = this.titleFn('modaltitle', section_id)) != null)
                        title = name;
                else if ((name = this.titleFn('sectiontitle', section_id)) != null)
                        title = '%s - %s'.format(parent.title, name);
                else if (!this.anonymous)
                        title = '%s - %s'.format(parent.title, section_id);

                for (var i = 0; i < this.children.length; i++) {
                        var o1 = this.children[i];

                        if (o1.modalonly === false)
                                continue;

                        var o2 = s.option(o1.constructor, o1.option, o1.title, o1.description);

                        for (var k in o1) {
                                if (!o1.hasOwnProperty(k))
                                        continue;

                                switch (k) {
                                case 'map':
                                case 'section':
                                case 'option':
                                case 'title':
                                case 'description':
                                        continue;

                                default:
                                        o2[k] = o1[k];
                                }
                        }
                }

                return Promise.resolve(this.addModalOptions(s, section_id, ev)).then(L.bind(m.render, m)).then(L.bind(function(nodes) {
                        ui.showModal(title, [
                                nodes,
                                E('div', { 'class': 'right' }, [
                                        E('button', {
                                                'class': 'btn',
                                                'click': ui.createHandlerFn(this, 'handleModalCancel', m)
                                        }, [ _('Dismiss') ]), ' ',
                                        E('button', {
                                                'class': 'cbi-button cbi-button-positive important',
                                                'click': ui.createHandlerFn(this, 'handleModalSave', m),
                                                'disabled': m.readonly || null
                                        }, [ _('Save') ])
                                ])
                        ], 'cbi-modal');
                }, this)).catch(L.error);
        }
});

/**
 * @class GridSection
 * @memberof LuCI.form
 * @augments LuCI.form.TableSection
 * @hideconstructor
 * @classdesc
 *
 * The `GridSection` class maps all or - if `filter()` is overwritten - a
 * subset of the underlying UCI configuration sections of a given type.
 *
 * A grid section functions similar to a {@link LuCI.form.TableSection} but
 * supports tabbing in the modal overlay. Option elements added with
 * [option()]{@link LuCI.form.GridSection#option} are shown in the table while
 * elements added with [taboption()]{@link LuCI.form.GridSection#taboption}
 * are displayed in the modal popup.
 *
 * Another important difference is that the table cells show a readonly text
 * preview of the corresponding option elements by default, unless the child
 * option element is explicitely made writable by setting the `editable`
 * property to `true`.
 *
 * Additionally, the grid section honours a `modalonly` property of child
 * option elements. Refer to the [AbstractValue]{@link LuCI.form.AbstractValue}
 * documentation for details.
 *
 * Layout wise, a grid section looks mostly identical to table sections.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [section()]{@link LuCI.form.Map#section}.
 *
 * @param {string} section_type
 * The type of the UCI section to map.
 *
 * @param {string} [title]
 * The title caption of the form section element.
 *
 * @param {string} [description]
 * The description text of the form section element.
 */
var CBIGridSection = CBITableSection.extend(/** @lends LuCI.form.GridSection.prototype */ {
        /**
         * Add an option tab to the section.
         *
         * The modal option elements of a grid section may be divided into multiple
         * tabs to provide a better overview to the user.
         *
         * Before options can be moved into a tab pane, the corresponding tab
         * has to be defined first, which is done by calling this function.
         *
         * Note that tabs are only effective in modal popups, options added with
         * `option()` will not be assigned to a specific tab and are rendered in
         * the table view only.
         *
         * @param {string} name
         * The name of the tab to register. It may be freely chosen and just serves
         * as an identifier to differentiate tabs.
         *
         * @param {string} title
         * The human readable caption of the tab.
         *
         * @param {string} [description]
         * An additional description text for the corresponding tab pane. It is
         * displayed as text paragraph below the tab but before the tab pane
         * contents. If omitted, no description will be rendered.
         *
         * @throws {Error}
         * Throws an exeption if a tab with the same `name` already exists.
         */
        tab: function(name, title, description) {
                CBIAbstractSection.prototype.tab.call(this, name, title, description);
        },

        /** @private */
        handleAdd: function(ev, name) {
                var config_name = this.uciconfig || this.map.config,
                    section_id = this.map.data.add(config_name, this.sectiontype, name);

                this.addedSection = section_id;
                return this.renderMoreOptionsModal(section_id);
        },

        /** @private */
        handleModalSave: function(/* ... */) {
                return this.super('handleModalSave', arguments)
                        .then(L.bind(function() { this.addedSection = null }, this));
        },

        /** @private */
        handleModalCancel: function(/* ... */) {
                var config_name = this.uciconfig || this.map.config;

                if (this.addedSection != null) {
                        this.map.data.remove(config_name, this.addedSection);
                        this.addedSection = null;
                }

                return this.super('handleModalCancel', arguments);
        },

        /** @private */
        renderUCISection: function(section_id) {
                return this.renderOptions(null, section_id);
        },

        /** @private */
        renderChildren: function(tab_name, section_id, in_table) {
                var tasks = [], index = 0;

                for (var i = 0, opt; (opt = this.children[i]) != null; i++) {
                        if (opt.disable || opt.modalonly)
                                continue;

                        if (opt.editable)
                                tasks.push(opt.render(index++, section_id, in_table));
                        else
                                tasks.push(this.renderTextValue(section_id, opt));
                }

                return Promise.all(tasks);
        },

        /** @private */
        renderTextValue: function(section_id, opt) {
                var title = this.stripTags(opt.title).trim(),
                    descr = this.stripTags(opt.description).trim(),
                    value = opt.textvalue(section_id);

                return E('div', {
                        'class': 'td cbi-value-field',
                        'data-title': (title != '') ? title : null,
                        'data-description': (descr != '') ? descr : null,
                        'data-name': opt.option,
                        'data-widget': opt.typename || opt.__name__
                }, (value != null) ? value : E('em', _('none')));
        },

        /** @private */
        renderHeaderRows: function(section_id) {
                return this.super('renderHeaderRows', [ NaN, true ]);
        },

        /** @private */
        renderRowActions: function(section_id) {
                return this.super('renderRowActions', [ section_id, _('Edit') ]);
        },

        /** @override */
        parse: function() {
                var section_ids = this.cfgsections(),
                    tasks = [];

                if (Array.isArray(this.children)) {
                        for (var i = 0; i < section_ids.length; i++) {
                                for (var j = 0; j < this.children.length; j++) {
                                        if (!this.children[j].editable || this.children[j].modalonly)
                                                continue;

                                        tasks.push(this.children[j].parse(section_ids[i]));
                                }
                        }
                }

                return Promise.all(tasks);
        }
});

/**
 * @class NamedSection
 * @memberof LuCI.form
 * @augments LuCI.form.AbstractSection
 * @hideconstructor
 * @classdesc
 *
 * The `NamedSection` class maps exactly one UCI section instance which is
 * specified when constructing the class instance.
 *
 * Layout and functionality wise, a named section is essentially a
 * `TypedSection` which allows exactly one section node.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [section()]{@link LuCI.form.Map#section}.
 *
 * @param {string} section_id
 * The name (ID) of the UCI section to map.
 *
 * @param {string} section_type
 * The type of the UCI section to map.
 *
 * @param {string} [title]
 * The title caption of the form section element.
 *
 * @param {string} [description]
 * The description text of the form section element.
 */
var CBINamedSection = CBIAbstractSection.extend(/** @lends LuCI.form.NamedSection.prototype */ {
        __name__: 'CBI.NamedSection',
        __init__: function(map, section_id /*, ... */) {
                this.super('__init__', this.varargs(arguments, 2, map));

                this.section = section_id;
        },

        /**
         * If set to `true`, the user may remove or recreate the sole mapped
         * configuration instance from the form section widget, otherwise only a
         * preexisting section may be edited. The default is `false`.
         *
         * @name LuCI.form.NamedSection.prototype#addremove
         * @type boolean
         * @default false
         */

        /**
         * Override the UCI configuration name to read the section IDs from. By
         * default, the configuration name is inherited from the parent `Map`.
         * By setting this property, a deviating configuration may be specified.
         * The default is `null`, means inheriting from the parent form.
         *
         * @name LuCI.form.NamedSection.prototype#uciconfig
         * @type string
         * @default null
         */

        /**
         * The `NamedSection` class overwrites the generic `cfgsections()`
         * implementation to return a one-element array containing the mapped
         * section ID as sole element. User code should not normally change this.
         *
         * @returns {string[]}
         * Returns a one-element array containing the mapped section ID.
         */
        cfgsections: function() {
                return [ this.section ];
        },

        /** @private */
        handleAdd: function(ev) {
                var section_id = this.section,
                    config_name = this.uciconfig || this.map.config;

                this.map.data.add(config_name, this.sectiontype, section_id);
                return this.map.save(null, true);
        },

        /** @private */
        handleRemove: function(ev) {
                var section_id = this.section,
                    config_name = this.uciconfig || this.map.config;

                this.map.data.remove(config_name, section_id);
                return this.map.save(null, true);
        },

        /** @private */
        renderContents: function(data) {
                var ucidata = data[0], nodes = data[1],
                    section_id = this.section,
                    config_name = this.uciconfig || this.map.config,
                    sectionEl = E('div', {
                                'id': ucidata ? null : 'cbi-%s-%s'.format(config_name, section_id),
                                'class': 'cbi-section',
                                'data-tab': (this.map.tabbed && !this.parentoption) ? this.sectiontype : null,
                                'data-tab-title': (this.map.tabbed && !this.parentoption) ? this.title || this.sectiontype : null
                        });

                if (typeof(this.title) === 'string' && this.title !== '')
                        sectionEl.appendChild(E('legend', {}, this.title));

                if (typeof(this.description) === 'string' && this.description !== '')
                        sectionEl.appendChild(E('div', { 'class': 'cbi-section-descr' }, this.description));

                if (ucidata) {
                        if (this.addremove) {
                                sectionEl.appendChild(
                                        E('div', { 'class': 'cbi-section-remove right' },
                                                E('button', {
                                                        'class': 'cbi-button',
                                                        'click': ui.createHandlerFn(this, 'handleRemove'),
                                                        'disabled': this.map.readonly || null
                                                }, [ _('Delete') ])));
                        }

                        sectionEl.appendChild(E('div', {
                                'id': 'cbi-%s-%s'.format(config_name, section_id),
                                'class': this.tabs
                                        ? 'cbi-section-node cbi-section-node-tabbed' : 'cbi-section-node',
                                'data-section-id': section_id
                        }, nodes));
                }
                else if (this.addremove) {
                        sectionEl.appendChild(
                                E('button', {
                                        'class': 'cbi-button cbi-button-add',
                                        'click': ui.createHandlerFn(this, 'handleAdd'),
                                        'disabled': this.map.readonly || null
                                }, [ _('Add') ]));
                }

                dom.bindClassInstance(sectionEl, this);

                return sectionEl;
        },

        /** @override */
        render: function() {
                var config_name = this.uciconfig || this.map.config,
                    section_id = this.section;

                return Promise.all([
                        this.map.data.get(config_name, section_id),
                        this.renderUCISection(section_id)
                ]).then(this.renderContents.bind(this));
        }
});

/**
 * @class Value
 * @memberof LuCI.form
 * @augments LuCI.form.AbstractValue
 * @hideconstructor
 * @classdesc
 *
 * The `Value` class represents a simple one-line form input using the
 * {@link LuCI.ui.Textfield} or - in case choices are added - the
 * {@link LuCI.ui.Combobox} class as underlying widget.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The name of the UCI option to map.
 *
 * @param {string} [title]
 * The title caption of the option element.
 *
 * @param {string} [description]
 * The description text of the option element.
 */
var CBIValue = CBIAbstractValue.extend(/** @lends LuCI.form.Value.prototype */ {
        __name__: 'CBI.Value',

        /**
         * If set to `true`, the field is rendered as password input, otherwise
         * as plain text input.
         *
         * @name LuCI.form.Value.prototype#password
         * @type boolean
         * @default false
         */

        /**
         * Set a placeholder string to use when the input field is empty.
         *
         * @name LuCI.form.Value.prototype#placeholder
         * @type string
         * @default null
         */

        /**
         * Add a predefined choice to the form option. By adding one or more
         * choices, the plain text input field is turned into a combobox widget
         * which prompts the user to select a predefined choice, or to enter a
         * custom value.
         *
         * @param {string} key
         * The choice value to add.
         *
         * @param {Node|string} value
         * The caption for the choice value. May be a DOM node, a document fragment
         * or a plain text string. If omitted, the `key` value is used as caption.
         */
        value: function(key, val) {
                this.keylist = this.keylist || [];
                this.keylist.push(String(key));

                this.vallist = this.vallist || [];
                this.vallist.push(dom.elem(val) ? val : String(val != null ? val : key));
        },

        /** @override */
        render: function(option_index, section_id, in_table) {
                return Promise.resolve(this.cfgvalue(section_id))
                        .then(this.renderWidget.bind(this, section_id, option_index))
                        .then(this.renderFrame.bind(this, section_id, in_table, option_index));
        },

        /** @private */
        renderFrame: function(section_id, in_table, option_index, nodes) {
                var config_name = this.uciconfig || this.section.uciconfig || this.map.config,
                    depend_list = this.transformDepList(section_id),
                    optionEl;

                if (in_table) {
                        var title = this.stripTags(this.title).trim();
                        optionEl = E('div', {
                                'class': 'td cbi-value-field',
                                'data-title': (title != '') ? title : null,
                                'data-description': this.stripTags(this.description).trim(),
                                'data-name': this.option,
                                'data-widget': this.typename || (this.template ? this.template.replace(/^.+\//, '') : null) || this.__name__
                        }, E('div', {
                                'id': 'cbi-%s-%s-%s'.format(config_name, section_id, this.option),
                                'data-index': option_index,
                                'data-depends': depend_list,
                                'data-field': this.cbid(section_id)
                        }));
                }
                else {
                        optionEl = E('div', {
                                'class': 'cbi-value',
                                'id': 'cbi-%s-%s-%s'.format(config_name, section_id, this.option),
                                'data-index': option_index,
                                'data-depends': depend_list,
                                'data-field': this.cbid(section_id),
                                'data-name': this.option,
                                'data-widget': this.typename || (this.template ? this.template.replace(/^.+\//, '') : null) || this.__name__
                        });

                        if (this.last_child)
                                optionEl.classList.add('cbi-value-last');

                        if (typeof(this.title) === 'string' && this.title !== '') {
                                optionEl.appendChild(E('label', {
                                        'class': 'cbi-value-title',
                                        'for': 'widget.cbid.%s.%s.%s'.format(config_name, section_id, this.option),
                                        'click': function(ev) {
                                                var node = ev.currentTarget,
                                                    elem = node.nextElementSibling.querySelector('#' + node.getAttribute('for')) || node.nextElementSibling.querySelector('[data-widget-id="' + node.getAttribute('for') + '"]');

                                                if (elem) {
                                                        elem.click();
                                                        elem.focus();
                                                }
                                        }
                                },
                                this.titleref ? E('a', {
                                        'class': 'cbi-title-ref',
                                        'href': this.titleref,
                                        'title': this.titledesc || _('Go to relevant configuration page')
                                }, this.title) : this.title));

                                optionEl.appendChild(E('div', { 'class': 'cbi-value-field' }));
                        }
                }

                if (nodes)
                        (optionEl.lastChild || optionEl).appendChild(nodes);

                if (!in_table && typeof(this.description) === 'string' && this.description !== '')
                        dom.append(optionEl.lastChild || optionEl,
                                E('div', { 'class': 'cbi-value-description' }, this.description));

                if (depend_list && depend_list.length)
                        optionEl.classList.add('hidden');

                optionEl.addEventListener('widget-change',
                        L.bind(this.map.checkDepends, this.map));

                dom.bindClassInstance(optionEl, this);

                return optionEl;
        },

        /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                var value = (cfgvalue != null) ? cfgvalue : this.default,
                    choices = this.transformChoices(),
                    widget;

                if (choices) {
                        var placeholder = (this.optional || this.rmempty)
                                ? E('em', _('unspecified')) : _('-- Please choose --');

                        widget = new ui.Combobox(Array.isArray(value) ? value.join(' ') : value, choices, {
                                id: this.cbid(section_id),
                                sort: this.keylist,
                                optional: this.optional || this.rmempty,
                                datatype: this.datatype,
                                select_placeholder: this.placeholder || placeholder,
                                validate: L.bind(this.validate, this, section_id),
                                disabled: (this.readonly != null) ? this.readonly : this.map.readonly
                        });
                }
                else {
                        widget = new ui.Textfield(Array.isArray(value) ? value.join(' ') : value, {
                                id: this.cbid(section_id),
                                password: this.password,
                                optional: this.optional || this.rmempty,
                                datatype: this.datatype,
                                placeholder: this.placeholder,
                                validate: L.bind(this.validate, this, section_id),
                                disabled: (this.readonly != null) ? this.readonly : this.map.readonly
                        });
                }

                return widget.render();
        }
});

/**
 * @class DynamicList
 * @memberof LuCI.form
 * @augments LuCI.form.Value
 * @hideconstructor
 * @classdesc
 *
 * The `DynamicList` class represents a multi value widget allowing the user
 * to enter multiple unique values, optionally selected from a set of
 * predefined choices. It builds upon the {@link LuCI.ui.DynamicList} widget.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The name of the UCI option to map.
 *
 * @param {string} [title]
 * The title caption of the option element.
 *
 * @param {string} [description]
 * The description text of the option element.
 */
var CBIDynamicList = CBIValue.extend(/** @lends LuCI.form.DynamicList.prototype */ {
        __name__: 'CBI.DynamicList',

        /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                var value = (cfgvalue != null) ? cfgvalue : this.default,
                    choices = this.transformChoices(),
                    items = L.toArray(value);

                var widget = new ui.DynamicList(items, choices, {
                        id: this.cbid(section_id),
                        sort: this.keylist,
                        optional: this.optional || this.rmempty,
                        datatype: this.datatype,
                        placeholder: this.placeholder,
                        validate: L.bind(this.validate, this, section_id),
                        disabled: (this.readonly != null) ? this.readonly : this.map.readonly
                });

                return widget.render();
        },
});

/**
 * @class ListValue
 * @memberof LuCI.form
 * @augments LuCI.form.Value
 * @hideconstructor
 * @classdesc
 *
 * The `ListValue` class implements a simple static HTML select element
 * allowing the user to chose a single value from a set of predefined choices.
 * It builds upon the {@link LuCI.ui.Select} widget.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The name of the UCI option to map.
 *
 * @param {string} [title]
 * The title caption of the option element.
 *
 * @param {string} [description]
 * The description text of the option element.
 */
var CBIListValue = CBIValue.extend(/** @lends LuCI.form.ListValue.prototype */ {
        __name__: 'CBI.ListValue',

        __init__: function() {
                this.super('__init__', arguments);
                this.widget = 'select';
                this.orientation = 'horizontal';
                this.deplist = [];
        },

        /**
         * Set the size attribute of the underlying HTML select element.
         *
         * @name LuCI.form.ListValue.prototype#size
         * @type number
         * @default null
         */

        /**
         * Set the type of the underlying form controls.
         *
         * May be one of `select` or `radio`. If set to `select`, an HTML
         * select element is rendered, otherwise a collection of `radio`
         * elements is used.
         *
         * @name LuCI.form.ListValue.prototype#widget
         * @type string
         * @default select
         */

        /**
         * Set the orientation of the underlying radio or checkbox elements.
         *
         * May be one of `horizontal` or `vertical`. Only applies to non-select
         * widget types.
         *
         * @name LuCI.form.ListValue.prototype#orientation
         * @type string
         * @default horizontal
         */

         /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                var choices = this.transformChoices();
                var widget = new ui.Select((cfgvalue != null) ? cfgvalue : this.default, choices, {
                        id: this.cbid(section_id),
                        size: this.size,
                        sort: this.keylist,
                        widget: this.widget,
                        optional: this.optional,
                        orientation: this.orientation,
                        placeholder: this.placeholder,
                        validate: L.bind(this.validate, this, section_id),
                        disabled: (this.readonly != null) ? this.readonly : this.map.readonly
                });

                return widget.render();
        },
});

/**
 * @class FlagValue
 * @memberof LuCI.form
 * @augments LuCI.form.Value
 * @hideconstructor
 * @classdesc
 *
 * The `FlagValue` element builds upon the {@link LuCI.ui.Checkbox} widget to
 * implement a simple checkbox element.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The name of the UCI option to map.
 *
 * @param {string} [title]
 * The title caption of the option element.
 *
 * @param {string} [description]
 * The description text of the option element.
 */
var CBIFlagValue = CBIValue.extend(/** @lends LuCI.form.FlagValue.prototype */ {
        __name__: 'CBI.FlagValue',

        __init__: function() {
                this.super('__init__', arguments);

                this.enabled = '1';
                this.disabled = '0';
                this.default = this.disabled;
        },

        /**
         * Sets the input value to use for the checkbox checked state.
         *
         * @name LuCI.form.FlagValue.prototype#enabled
         * @type number
         * @default 1
         */

        /**
         * Sets the input value to use for the checkbox unchecked state.
         *
         * @name LuCI.form.FlagValue.prototype#disabled
         * @type number
         * @default 0
         */

        /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                var widget = new ui.Checkbox((cfgvalue != null) ? cfgvalue : this.default, {
                        id: this.cbid(section_id),
                        value_enabled: this.enabled,
                        value_disabled: this.disabled,
                        validate: L.bind(this.validate, this, section_id),
                        disabled: (this.readonly != null) ? this.readonly : this.map.readonly
                });

                return widget.render();
        },

        /**
         * Query the checked state of the underlying checkbox widget and return
         * either the `enabled` or the `disabled` property value, depending on
         * the checked state.
         *
         * @override
         */
        formvalue: function(section_id) {
                var elem = this.getUIElement(section_id),
                    checked = elem ? elem.isChecked() : false;
                return checked ? this.enabled : this.disabled;
        },

        /**
         * Query the checked state of the underlying checkbox widget and return
         * either a localized `Yes` or `No` string, depending on the checked state.
         *
         * @override
         */
        textvalue: function(section_id) {
                var cval = this.cfgvalue(section_id);

                if (cval == null)
                        cval = this.default;

                return (cval == this.enabled) ? _('Yes') : _('No');
        },

        /** @override */
        parse: function(section_id) {
                if (this.isActive(section_id)) {
                        var fval = this.formvalue(section_id);

                        if (!this.isValid(section_id)) {
                                var title = this.stripTags(this.title).trim();
                                return Promise.reject(new TypeError(_('Option "%s" contains an invalid input value.').format(title || this.option)));
                        }

                        if (fval == this.default && (this.optional || this.rmempty))
                                return Promise.resolve(this.remove(section_id));
                        else
                                return Promise.resolve(this.write(section_id, fval));
                }
                else {
                        return Promise.resolve(this.remove(section_id));
                }
        },
});

/**
 * @class MultiValue
 * @memberof LuCI.form
 * @augments LuCI.form.DynamicList
 * @hideconstructor
 * @classdesc
 *
 * The `MultiValue` class is a modified variant of the `DynamicList` element
 * which leverages the {@link LuCI.ui.Dropdown} widget to implement a multi
 * select dropdown element.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The name of the UCI option to map.
 *
 * @param {string} [title]
 * The title caption of the option element.
 *
 * @param {string} [description]
 * The description text of the option element.
 */
var CBIMultiValue = CBIDynamicList.extend(/** @lends LuCI.form.MultiValue.prototype */ {
        __name__: 'CBI.MultiValue',

        __init__: function() {
                this.super('__init__', arguments);
                this.placeholder = _('-- Please choose --');
        },

        /**
         * Allows to specify the [display_items]{@link LuCI.ui.Dropdown.InitOptions}
         * property of the underlying dropdown widget. If omitted, the value of
         * the `size` property is used or `3` when `size` is unspecified as well.
         *
         * @name LuCI.form.MultiValue.prototype#display_size
         * @type number
         * @default null
         */

        /**
         * Allows to specify the [dropdown_items]{@link LuCI.ui.Dropdown.InitOptions}
         * property of the underlying dropdown widget. If omitted, the value of
         * the `size` property is used or `-1` when `size` is unspecified as well.
         *
         * @name LuCI.form.MultiValue.prototype#dropdown_size
         * @type number
         * @default null
         */

        /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                var value = (cfgvalue != null) ? cfgvalue : this.default,
                    choices = this.transformChoices();

                var widget = new ui.Dropdown(L.toArray(value), choices, {
                        id: this.cbid(section_id),
                        sort: this.keylist,
                        multiple: true,
                        optional: this.optional || this.rmempty,
                        select_placeholder: this.placeholder,
                        display_items: this.display_size || this.size || 3,
                        dropdown_items: this.dropdown_size || this.size || -1,
                        validate: L.bind(this.validate, this, section_id),
                        disabled: (this.readonly != null) ? this.readonly : this.map.readonly
                });

                return widget.render();
        },
});

/**
 * @class TextValue
 * @memberof LuCI.form
 * @augments LuCI.form.Value
 * @hideconstructor
 * @classdesc
 *
 * The `TextValue` class implements a multi-line textarea input using
 * {@link LuCI.ui.Textarea}.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The name of the UCI option to map.
 *
 * @param {string} [title]
 * The title caption of the option element.
 *
 * @param {string} [description]
 * The description text of the option element.
 */
var CBITextValue = CBIValue.extend(/** @lends LuCI.form.TextValue.prototype */ {
        __name__: 'CBI.TextValue',

        /** @ignore */
        value: null,

        /**
         * Enforces the use of a monospace font for the textarea contents when set
         * to `true`.
         *
         * @name LuCI.form.TextValue.prototype#monospace
         * @type boolean
         * @default false
         */

        /**
         * Allows to specify the [cols]{@link LuCI.ui.Textarea.InitOptions}
         * property of the underlying textarea widget.
         *
         * @name LuCI.form.TextValue.prototype#cols
         * @type number
         * @default null
         */

        /**
         * Allows to specify the [rows]{@link LuCI.ui.Textarea.InitOptions}
         * property of the underlying textarea widget.
         *
         * @name LuCI.form.TextValue.prototype#rows
         * @type number
         * @default null
         */

        /**
         * Allows to specify the [wrap]{@link LuCI.ui.Textarea.InitOptions}
         * property of the underlying textarea widget.
         *
         * @name LuCI.form.TextValue.prototype#wrap
         * @type number
         * @default null
         */

        /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                var value = (cfgvalue != null) ? cfgvalue : this.default;

                var widget = new ui.Textarea(value, {
                        id: this.cbid(section_id),
                        optional: this.optional || this.rmempty,
                        placeholder: this.placeholder,
                        monospace: this.monospace,
                        cols: this.cols,
                        rows: this.rows,
                        wrap: this.wrap,
                        validate: L.bind(this.validate, this, section_id),
                        disabled: (this.readonly != null) ? this.readonly : this.map.readonly
                });

                return widget.render();
        }
});

/**
 * @class DummyValue
 * @memberof LuCI.form
 * @augments LuCI.form.Value
 * @hideconstructor
 * @classdesc
 *
 * The `DummyValue` element wraps an {@link LuCI.ui.Hiddenfield} widget and
 * renders the underlying UCI option or default value as readonly text.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The name of the UCI option to map.
 *
 * @param {string} [title]
 * The title caption of the option element.
 *
 * @param {string} [description]
 * The description text of the option element.
 */
var CBIDummyValue = CBIValue.extend(/** @lends LuCI.form.DummyValue.prototype */ {
        __name__: 'CBI.DummyValue',

        /**
         * Set an URL which is opened when clicking on the dummy value text.
         *
         * By setting this property, the dummy value text is wrapped in an `<a>`
         * element with the property value used as `href` attribute.
         *
         * @name LuCI.form.DummyValue.prototype#href
         * @type string
         * @default null
         */

        /**
         * Treat the UCI option value (or the `default` property value) as HTML.
         *
         * By default, the value text is HTML escaped before being rendered as
         * text. In some cases it may be needed to actually interpret and render
         * HTML contents as-is. When set to `true`, HTML escaping is disabled.
         *
         * @name LuCI.form.DummyValue.prototype#rawhtml
         * @type boolean
         * @default null
         */

        /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                var value = (cfgvalue != null) ? cfgvalue : this.default,
                    hiddenEl = new ui.Hiddenfield(value, { id: this.cbid(section_id) }),
                    outputEl = E('div');

                if (this.href && !((this.readonly != null) ? this.readonly : this.map.readonly))
                        outputEl.appendChild(E('a', { 'href': this.href }));

                dom.append(outputEl.lastChild || outputEl,
                        this.rawhtml ? value : [ value ]);

                return E([
                        outputEl,
                        hiddenEl.render()
                ]);
        },

        /** @override */
        remove: function() {},

        /** @override */
        write: function() {}
});

/**
 * @class ButtonValue
 * @memberof LuCI.form
 * @augments LuCI.form.Value
 * @hideconstructor
 * @classdesc
 *
 * The `DummyValue` element wraps an {@link LuCI.ui.Hiddenfield} widget and
 * renders the underlying UCI option or default value as readonly text.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The name of the UCI option to map.
 *
 * @param {string} [title]
 * The title caption of the option element.
 *
 * @param {string} [description]
 * The description text of the option element.
 */
var CBIButtonValue = CBIValue.extend(/** @lends LuCI.form.ButtonValue.prototype */ {
        __name__: 'CBI.ButtonValue',

        /**
         * Override the rendered button caption.
         *
         * By default, the option title - which is passed as fourth argument to the
         * constructor - is used as caption for the button element. When setting
         * this property to a string, it is used as `String.format()` pattern with
         * the underlying UCI section name passed as first format argument. When
         * set to a function, it is invoked passing the section ID as sole argument
         * and the resulting return value is converted to a string before being
         * used as button caption.
         *
         * The default is `null`, means the option title is used as caption.
         *
         * @name LuCI.form.ButtonValue.prototype#inputtitle
         * @type string|function
         * @default null
         */

        /**
         * Override the button style class.
         *
         * By setting this property, a specific `cbi-button-*` CSS class can be
         * selected to influence the style of the resulting button.
         *
         * Suitable values which are implemented by most themes are `positive`,
         * `negative` and `primary`.
         *
         * The default is `null`, means a neutral button styling is used.
         *
         * @name LuCI.form.ButtonValue.prototype#inputstyle
         * @type string
         * @default null
         */

        /**
         * Override the button click action.
         *
         * By default, the underlying UCI option (or default property) value is
         * copied into a hidden field tied to the button element and the save
         * action is triggered on the parent form element.
         *
         * When this property is set to a function, it is invoked instead of
         * performing the default actions. The handler function will receive the
         * DOM click element as first and the underlying configuration section ID
         * as second argument.
         *
         * @name LuCI.form.ButtonValue.prototype#onclick
         * @type function
         * @default null
         */

        /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                var value = (cfgvalue != null) ? cfgvalue : this.default,
                    hiddenEl = new ui.Hiddenfield(value, { id: this.cbid(section_id) }),
                    outputEl = E('div'),
                    btn_title = this.titleFn('inputtitle', section_id) || this.titleFn('title', section_id);

                if (value !== false)
                        dom.content(outputEl, [
                                E('button', {
                                        'class': 'cbi-button cbi-button-%s'.format(this.inputstyle || 'button'),
                                        'click': ui.createHandlerFn(this, function(section_id, ev) {
                                                if (this.onclick)
                                                        return this.onclick(ev, section_id);

                                                ev.currentTarget.parentNode.nextElementSibling.value = value;
                                                return this.map.save();
                                        }, section_id),
                                        'disabled': ((this.readonly != null) ? this.readonly : this.map.readonly) || null
                                }, [ btn_title ])
                        ]);
                else
                        dom.content(outputEl, ' - ');

                return E([
                        outputEl,
                        hiddenEl.render()
                ]);
        }
});

/**
 * @class HiddenValue
 * @memberof LuCI.form
 * @augments LuCI.form.Value
 * @hideconstructor
 * @classdesc
 *
 * The `HiddenValue` element wraps an {@link LuCI.ui.Hiddenfield} widget.
 *
 * Hidden value widgets used to be necessary in legacy code which actually
 * submitted the underlying HTML form the server. With client side handling of
 * forms, there are more efficient ways to store hidden state data.
 *
 * Since this widget has no visible content, the title and description values
 * of this form element should be set to `null` as well to avoid a broken or
 * distorted form layout when rendering the option element.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The name of the UCI option to map.
 *
 * @param {string} [title]
 * The title caption of the option element.
 *
 * @param {string} [description]
 * The description text of the option element.
 */
var CBIHiddenValue = CBIValue.extend(/** @lends LuCI.form.HiddenValue.prototype */ {
        __name__: 'CBI.HiddenValue',

        /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                var widget = new ui.Hiddenfield((cfgvalue != null) ? cfgvalue : this.default, {
                        id: this.cbid(section_id)
                });

                return widget.render();
        }
});

/**
 * @class FileUpload
 * @memberof LuCI.form
 * @augments LuCI.form.Value
 * @hideconstructor
 * @classdesc
 *
 * The `FileUpload` element wraps an {@link LuCI.ui.FileUpload} widget and
 * offers the ability to browse, upload and select remote files.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The name of the UCI option to map.
 *
 * @param {string} [title]
 * The title caption of the option element.
 *
 * @param {string} [description]
 * The description text of the option element.
 */
var CBIFileUpload = CBIValue.extend(/** @lends LuCI.form.FileUpload.prototype */ {
        __name__: 'CBI.FileSelect',

        __init__: function(/* ... */) {
                this.super('__init__', arguments);

                this.show_hidden = false;
                this.enable_upload = true;
                this.enable_remove = true;
                this.root_directory = '/etc/luci-uploads';
        },

        /**
         * Toggle display of hidden files.
         *
         * Display hidden files when rendering the remote directory listing.
         * Note that this is merely a cosmetic feature, hidden files are always
         * included in received remote file listings.
         *
         * The default is `false`, means hidden files are not displayed.
         *
         * @name LuCI.form.FileUpload.prototype#show_hidden
         * @type boolean
         * @default false
         */

        /**
         * Toggle file upload functionality.
         *
         * When set to `true`, the underlying widget provides a button which lets
         * the user select and upload local files to the remote system.
         * Note that this is merely a cosmetic feature, remote upload access is
         * controlled by the session ACL rules.
         *
         * The default is `true`, means file upload functionality is displayed.
         *
         * @name LuCI.form.FileUpload.prototype#enable_upload
         * @type boolean
         * @default true
         */

        /**
         * Toggle remote file delete functionality.
         *
         * When set to `true`, the underlying widget provides a buttons which let
         * the user delete files from remote directories. Note that this is merely
         * a cosmetic feature, remote delete permissions are controlled by the
         * session ACL rules.
         *
         * The default is `true`, means file removal buttons are displayed.
         *
         * @name LuCI.form.FileUpload.prototype#enable_remove
         * @type boolean
         * @default true
         */

        /**
         * Specify the root directory for file browsing.
         *
         * This property defines the topmost directory the file browser widget may
         * navigate to, the UI will not allow browsing directories outside this
         * prefix. Note that this is merely a cosmetic feature, remote file access
         * and directory listing permissions are controlled by the session ACL
         * rules.
         *
         * The default is `/etc/luci-uploads`.
         *
         * @name LuCI.form.FileUpload.prototype#root_directory
         * @type string
         * @default /etc/luci-uploads
         */

        /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                var browserEl = new ui.FileUpload((cfgvalue != null) ? cfgvalue : this.default, {
                        id: this.cbid(section_id),
                        name: this.cbid(section_id),
                        show_hidden: this.show_hidden,
                        enable_upload: this.enable_upload,
                        enable_remove: this.enable_remove,
                        root_directory: this.root_directory,
                        disabled: (this.readonly != null) ? this.readonly : this.map.readonly
                });

                return browserEl.render();
        }
});

/**
 * @class SectionValue
 * @memberof LuCI.form
 * @augments LuCI.form.Value
 * @hideconstructor
 * @classdesc
 *
 * The `SectionValue` widget embeds a form section element within an option
 * element container, allowing to nest form sections into other sections.
 *
 * @param {LuCI.form.Map|LuCI.form.JSONMap} form
 * The configuration form this section is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {LuCI.form.AbstractSection} section
 * The configuration section this option is added to. It is automatically passed
 * by [option()]{@link LuCI.form.AbstractSection#option} or
 * [taboption()]{@link LuCI.form.AbstractSection#taboption} when adding the
 * option to the section.
 *
 * @param {string} option
 * The internal name of the option element holding the section. Since a section
 * container element does not read or write any configuration itself, the name
 * is only used internally and does not need to relate to any underlying UCI
 * option name.
 *
 * @param {LuCI.form.AbstractSection} subsection_class
 * The class to use for instantiating the nested section element. Note that
 * the class value itself is expected here, not a class instance obtained by
 * calling `new`. The given class argument must be a subclass of the
 * `AbstractSection` class.
 *
 * @param {...*} [class_args]
 * All further arguments are passed as-is to the subclass constructor. Refer
 * to the corresponding class constructor documentations for details.
 */
var CBISectionValue = CBIValue.extend(/** @lends LuCI.form.SectionValue.prototype */ {
        __name__: 'CBI.ContainerValue',
        __init__: function(map, section, option, cbiClass /*, ... */) {
                this.super('__init__', [map, section, option]);

                if (!CBIAbstractSection.isSubclass(cbiClass))
                        throw 'Sub section must be a descendent of CBIAbstractSection';

                this.subsection = cbiClass.instantiate(this.varargs(arguments, 4, this.map));
                this.subsection.parentoption = this;
        },

        /**
         * Access the embedded section instance.
         *
         * This property holds a reference to the instantiated nested section.
         *
         * @name LuCI.form.SectionValue.prototype#subsection
         * @type LuCI.form.AbstractSection
         * @readonly
         */

        /** @override */
        load: function(section_id) {
                return this.subsection.load();
        },

        /** @override */
        parse: function(section_id) {
                return this.subsection.parse();
        },

        /** @private */
        renderWidget: function(section_id, option_index, cfgvalue) {
                return this.subsection.render();
        },

        /** @private */
        checkDepends: function(section_id) {
                this.subsection.checkDepends();
                return CBIValue.prototype.checkDepends.apply(this, [ section_id ]);
        },

        /**
         * Since the section container is not rendering an own widget,
         * its `value()` implementation is a no-op.
         *
         * @override
         */
        value: function() {},

        /**
         * Since the section container is not tied to any UCI configuration,
         * its `write()` implementation is a no-op.
         *
         * @override
         */
        write: function() {},

        /**
         * Since the section container is not tied to any UCI configuration,
         * its `remove()` implementation is a no-op.
         *
         * @override
         */
        remove: function() {},

        /**
         * Since the section container is not tied to any UCI configuration,
         * its `cfgvalue()` implementation will always return `null`.
         *
         * @override
         * @returns {null}
         */
        cfgvalue: function() { return null },

        /**
         * Since the section container is not tied to any UCI configuration,
         * its `formvalue()` implementation will always return `null`.
         *
         * @override
         * @returns {null}
         */
        formvalue: function() { return null }
});

/**
 * @class form
 * @memberof LuCI
 * @hideconstructor
 * @classdesc
 *
 * The LuCI form class provides high level abstractions for creating creating
 * UCI- or JSON backed configurations forms.
 *
 * To import the class in views, use `'require form'`, to import it in
 * external JavaScript, use `L.require("form").then(...)`.
 *
 * A typical form is created by first constructing a
 * {@link LuCI.form.Map} or {@link LuCI.form.JSONMap} instance using `new` and
 * by subsequently adding sections and options to it. Finally
 * [render()]{@link LuCI.form.Map#render} is invoked on the instance to
 * assemble the HTML markup and insert it into the DOM.
 *
 * Example:
 *
 * <pre>
 * 'use strict';
 * 'require form';
 *
 * var m, s, o;
 *
 * m = new form.Map('example', 'Example form',
 *      'This is an example form mapping the contents of /etc/config/example');
 *
 * s = m.section(form.NamedSection, 'first_section', 'example', 'The first section',
 *      'This sections maps "config example first_section" of /etc/config/example');
 *
 * o = s.option(form.Flag, 'some_bool', 'A checkbox option');
 *
 * o = s.option(form.ListValue, 'some_choice', 'A select element');
 * o.value('choice1', 'The first choice');
 * o.value('choice2', 'The second choice');
 *
 * m.render().then(function(node) {
 *      document.body.appendChild(node);
 * });
 * </pre>
 */
return baseclass.extend(/** @lends LuCI.form.prototype */ {
        Map: CBIMap,
        JSONMap: CBIJSONMap,
        AbstractSection: CBIAbstractSection,
        AbstractValue: CBIAbstractValue,

        TypedSection: CBITypedSection,
        TableSection: CBITableSection,
        GridSection: CBIGridSection,
        NamedSection: CBINamedSection,

        Value: CBIValue,
        DynamicList: CBIDynamicList,
        ListValue: CBIListValue,
        Flag: CBIFlagValue,
        MultiValue: CBIMultiValue,
        TextValue: CBITextValue,
        DummyValue: CBIDummyValue,
        Button: CBIButtonValue,
        HiddenValue: CBIHiddenValue,
        FileUpload: CBIFileUpload,
        SectionValue: CBISectionValue
});