#!/bin/sh
set -euf

BACKLIGHT_PATH="/sys/class/backlight/amdgpu_bl0"

errecho() {
	>&2 printf '%s\n' "$*"
}

usage() {
	errecho "\
Usage: ${0##*/} [-hq] [-s VALUE] [-c VALUE]
No arguments: Print current brightness and exit
If -s and -c are specified, -c takes priority

 -h         show this help
 -q         print current brightness to stdout and exit
 -s <VALUE> set brightness to VALUE
 -c <VALUE> change brightness by VALUE"
 	exit 0
}

nb=
mb="$(cat "$BACKLIGHT_PATH/max_brightness")"
cb="$(cat "$BACKLIGHT_PATH/brightness")"
while getopts :hqs:c: OPT; do
	case $OPT in
		h) usage ;;
		q) echo "$cb" && exit 0 ;;
		s) nb=$OPTARG ;;
		c) nb=$((cb + OPTARG)) ;;
		*) exit 1 ;;
	esac
done
errecho "Current brightness: $cb"

[ -z "$nb" ] && errecho "Brightness not changed" && exit 0
[ "$nb" -gt "$mb" ] && nb=$mb
[ "$nb" -lt 0 ] && nb=0

printf '%s' "$nb" > "$BACKLIGHT_PATH/brightness" && errecho "New brightness: $nb" || errecho "Error setting brightness!"