#!/bin/sh
set -eu

usage() {
	cat <<-'EOF'
		Usage:
		  volume ACTION
		  volume -h
	EOF
}

help() {
	cat <<-'EOF'


		Options:
		  -h, --help    show this message

		  ACTION        one of:
		                - up
		                - down
		                - toggle
		                - rotate


		Manage the audio output.


		Examples:

		  Increase the volume:

		    $ volume up


		  Toggle mute/unmute in the current audio output:

		    $ volume toggle


		  Change the audio output:

		    $ volume rotate
	EOF
}

for flag in "$@"; do
	case "$flag" in
		(--)
			break
			;;
		(--help)
			usage
			help
			exit
			;;
		(*)
			;;
	esac
done

while getopts 'h' flag; do
	case "$flag" in
		(h)
			usage
			help
			exit
			;;
		(*)
			usage >&2
			exit 2
			;;
	esac
done
shift $((OPTIND - 1))
ACTION="${1:-}"

eval "$(assert-arg -- "$ACTION" 'ACTION')"


rotate() {
	# This script assumes that at most 2 sinks exist at any time.
	# When this premise is no longer true, it needs to be upgraded.

	CURRENT="$(pacmd list-sinks | grep '\* index' | cut -d: -f2 | tr -d ' ')"
	OTHER="$(pacmd list-sinks | grep index | grep -v '\* index' | tail -n1 | cut -d: -f2 | tr -d ' ')"

	if [ "$CURRENT" = 0 ]; then
		pacmd set-default-sink "$OTHER"
	else
		pacmd set-default-sink 0
	fi
}

case "$ACTION" in
	up)
		pactl set-sink-volume @DEFAULT_SINK@ +10%
		;;
	down)
		pactl set-sink-volume @DEFAULT_SINK@ -10%
		;;
	toggle)
		pactl set-sink-mute @DEFAULT_SINK@ toggle
		;;
	rotate)
		rotate
		;;
	*)
		printf 'Bad ACTION: %s.\n\n' "$ACTION" >&2
		usage >&2
		exit 2
		;;
esac