#!/usr/bin/env bash
BASEDIR="$PWD"
ENVDIR="$PWD/env"

usage() {
	cat <<EOF
Usage: $0 [options] <command> [arguments]
Commands:
	help              This help text
	list              List environments
	clear             Delete all environment and revert to flat config/files
	new <name>        Create a new environment
	switch <name>     Switch to a different environment
	delete <name>     Delete an environment
	rename <newname>  Rename the current environment
	diff              Show differences between current state and environment
	save              Save your changes to the environment
	revert            Revert your changes since last save

Options:

EOF
	exit ${1:-1}
}

error() {
	echo "$0: $*"
	exit 1
}

ask_bool() {
	local DEFAULT="$1"; shift
	local def defstr val
	case "$DEFAULT" in
		1) def=0; defstr="Y/n";;
		0) def=1; defstr="y/N";;
		*) def=;  defstr="y/n";;
	esac
	while [ -z "$val" ]; do
		local VAL

		echo -n "$* ($defstr): "
		read VAL
		case "$VAL" in
			y*|Y*) val=0;;
			n*|N*) val=1;;
			*) val="$def";;
		esac
	done
	return "$val"
}

env_init() {
	local CREATE="$1"
	if [ -z "$CREATE" ]; then
		[ -d "$ENVDIR" ] || exit 0
	fi
	[ -x "$(which git 2>/dev/null)" ] || error "Git is not installed"
	mkdir -p "$ENVDIR" || error "Failed to create the environment directory"
	cd "$ENVDIR" || error "Failed to switch to the environment directory"
	[ -d .git ] || { 
		git init &&
		touch .config &&
		mkdir files &&
		git add . && 
		git commit -q -m "Initial import"
	} || {
		rm -rf .git
		error "Failed to initialize the environment directory"
	}
}

env_sync_data() {
	[ \! -L "$BASEDIR/.config" -a -f "$BASEDIR/.config" ] && mv "$BASEDIR/.config" "$ENVDIR"
	git add .
	git add -u
}

env_sync() {
	local STR="$1"
	env_sync_data
	git commit -m "${STR:-Update} at $(date)"
}

env_link_config() {
	rm -f "$BASEDIR/.config"
	ln -s env/.config "$BASEDIR/.config"
	mkdir -p "$ENVDIR/files"
	[ -L "$BASEDIR/files" ] || ln -s env/files "$BASEDIR/files"
}

env_do_reset() {
	git reset --hard HEAD
	git clean -d -f
}

env_list() {
	env_init
	git branch | grep -vE '^. master$'
}

env_diff() {
	env_init
	env_sync_data
	git diff --cached
    env_link_config
}

env_save() {
	env_init
	env_sync
	env_link_config
}

env_revert() {
	env_init
	env_do_reset
	env_link_config
}

env_ask_sync() {
	env_sync_data
	LINES="$(env_diff | wc -l)" # implies env_init
	[ "$LINES" -gt 0 ] && {
		if ask_bool 1 "Do you want to save your changes"; then
			env_sync
		else
			env_do_reset
		fi
	}
}

env_clear() {
	env_init
	[ -L "$BASEDIR/.config" ] && rm -f "$BASEDIR/.config"
	[ -L "$BASEDIR/files" ] && rm -f "$BASEDIR/files"
	[ -f "$ENVDIR/.config" ] || ( cd "$ENVDIR/files" && find | grep -vE '^\.$' > /dev/null )
	env_sync_data
	if ask_bool 1 "Do you want to keep your current config and files"; then
		mkdir -p "$BASEDIR/files"
		cp -a "$ENVDIR/files/*" "$BASEDIR/files" 2>/dev/null >/dev/null
		cp "$ENVDIR/.config" "$BASEDIR/"
	else
		rm -rf "$BASEDIR/files" "$BASEDIR/.config"
	fi
	cd "$BASEDIR"
	rm -rf "$ENVDIR"
}

env_delete() {
	local name="${1##*/}"
	env_init
	[ -z "$name" ] && usage
	branch="$(git branch | grep '^\* ' | awk '{print $2}')"
	[ "$name" = "$branch" ] && error "cannot delete the currently selected environment"
	git branch -D "$name"
}

env_switch() {
	local name="${1##*/}"
	[ -z "$name" ] && usage

	env_init
	env_ask_sync
	git checkout "$name" || error "environment '$name' not found"
	env_link_config
}

env_rename() {
	local NAME="${1##*/}"
	env_init
	git branch -m "$NAME"
}

env_new() {
	local NAME="$1"
	local branch
	local from="master"

	[ -z "$NAME" ] && usage
	env_init 1
	
	branch="$(git branch | grep '^\* ' | awk '{print $2}')"
	if [ -n "$branch" -a "$branch" != "master" ]; then
		env_ask_sync
		if ask_bool 0 "Do you want to clone the current environment?"; then
			from="$branch"
		fi
		rm -f "$BASEDIR/.config" "$BASEDIR/files"
	fi
	git checkout -b "$1" "$from"
	if [ -f "$BASEDIR/.config" -o -d "$BASEDIR/files" ]; then
		if ask_bool 1 "Do you want to keep your current config and files?"; then
			[ -d "$BASEDIR/files" -a \! -L "$BASEDIR/files" ] && {
				mv "$BASEDIR/files/"* "$ENVDIR/" 2>/dev/null
				rmdir "$BASEDIR/files"
			}
			env_sync
		else
			rm -rf "$BASEDIR/.config" "$BASEDIR/files"
		fi
	fi
	env_link_config
}

COMMAND="$1"; shift
case "$COMMAND" in
	help) usage 0;;
	new) env_new "$@";;
	list) env_list "$@";;
	clear) env_clear "$@";;
	switch) env_switch "$@";;
	delete) env_delete "$@";;
	rename) env_rename "$@";;
	diff) env_diff "$@";;
	save) env_save "$@";;
	revert) env_revert "$@";;
	*) usage;;
esac