#!/bin/sh

# wpPointer.sh: Set next or previous wallpaper in wallpaper history or set and add one to it
#
# Usage: wpPointer.sh [-n|p] [-o] FILE...
#
# -n sets next wallpaper if it exists
# -p sets previous wallpaper if it exists
# -o opens recorded wallpapers in sxiv

usageMessage="Usage: ${0} [-n|p] [-o] FILE..."

wpDatFile="$CONFIG_WPLIST"
wpPointerFile="$CONFIG_WPPOINTER"
recordedMax="30"

nextOrPrev=""
next="n"
prev="p"

open=""

error() {
	printf '%s error: %s\n' "$0" "$*" >&2
	notify-send "${0} error" "$*"
}

errorAndUsage() {
	printf '%s error: %s\n%s\n' "$0" "$*" "$usageMessage" >&2
	notify-send "${0} error" "${*}\n\n${usageMessage}"
}

getRecordedAmount() {
	wc -l "$wpDatFile" | cut -d' ' -f1
}

setWP() {
	wp="$1"
	feh --bg-max "$wp"
	ln -sf "$wp" "${HOME}/wp"
}

setWpByPointer() {
	pointer="$1"
	wp="$(sed -n "${pointer}p" "$wpDatFile")"
	echo "$pointer" >"$wpPointerFile"
	if ! setWP "$wp"; then
		error "Unable to set ${wp} as wallpaper."
	fi
}

setNextOrPrev() {

	nextOrPrev="$1"

	if ! [ -f "$wpDatFile" ]; then
		error "${wpDatFile} does not exist or is not a regular file. Maybe no wallpapers were registered yet."
		exit 2
	fi

	if ! [ -s "$wpDatFile" ]; then
		error "${wpDatFile} is empty."
		exit 2
	fi

	datFileLength="$(getRecordedAmount)"

	if [ -f "$wpPointerFile" ]; then
		pointer="$(cat "$wpPointerFile")"
	else
		pointer="$datFileLength"
	fi

	if [ "$nextOrPrev" = "$next" ]; then

		if [ "$pointer" -eq "$datFileLength" ]; then
			error 'Last recorded wallpaper already selected.'
			exit 3
		fi

		pointer=$((pointer+1))
		setWpByPointer "$pointer"

	fi

	if [ "$nextOrPrev" = "$prev" ]; then

		if [ "$pointer" -eq "1" ]; then
			error 'First recorded wallpaper already selected.'
			exit 3
		fi

		pointer=$((pointer-1))
		setWpByPointer "$pointer"

	fi

}

addWp() {

	wp="$1"

	if ! [ -f "$1" ]; then
		error "File ${1} does not exist."
		exit 4
	fi

	if ! setWP "$wp"; then
		error "Unable to set ${wp} as wallpaper."
		exit 4
	fi

	wpPath="$(readlink -f "$wp")"
	# Double \ for explicit \ to reach variable!
	wpPathSanitized="$(echo "$wpPath" | sed 's|/|\\/|g')"

	# Delete existing references to the wallpaper to avoid repetition in history
	sed -i "/^${wpPathSanitized}$/d" "$wpDatFile"

	echo "$wpPath" >>"$wpDatFile"
	[ "$(getRecordedAmount)" -gt "$recordedMax" ] && sed -i "1d" "$wpDatFile"
	getRecordedAmount >"$wpPointerFile"

}

# Check pointer file makes sense

if [ -f "$wpPointerFile" ]; then
	pointer="$(cat "$wpPointerFile")"
	pointerAsNumber="$(echo "$pointer" | sed 1q | grep -E '[0-9]+')"
	if [ "$pointer" != "$pointerAsNumber" ]; then
		rm "$wpPointerFile"
	else
		if [ "$pointer" -lt 1 ]; then
			echo "1" >"$wpPointerFile"
		fi
		recordedAmount=$(getRecordedAmount)
		if [ "$pointer" -gt "$recordedAmount" ]; then
			echo "$recordedAmount" >"$wpPointerFile"
		fi
	fi
fi

# Process options

while getopts ':npo' opt; do
	case $opt in

		'n' )
			if [ -n "$nextOrPrev" ]; then
				errorAndUsage 'Tried to use -n and -p at the same time.'
				exit 1
			fi
			setNextOrPrev "$next"
			;;

		'p' )
			if [ -n "$nextOrPrev" ]; then
				errorAndUsage 'Tried to use -n and -p at the same time.'
				exit 1
			fi
			setNextOrPrev "$prev"
			;;

		'o' )
			open="y"
			;;

		'?' )
			printf '%s\n' "$usageMessage"
			exit 1

	esac
done
shift $((OPTIND - 1))

# Set and add arguments to wallpaper history

for wp in "$@"; do
	addWp "$wp"
done

[ -n "$open" ] && sxiv -b -t -n "$(getRecordedAmount)" - <"$wpDatFile"