#!/bin/bash -e
shopt -s extglob nullglob

set_brightness() {
    local max; max="$(cat "$1"/max_brightness)"
    local file="$1"/brightness
    local val="$(($2 * max / 100 + 1))"

    [ "$val" -lt 0      ] && val=0
    [ "$val" -gt "$max" ] && val="$max"
    echo "$val" > "$file"
}

CUR_FILE="${XDG_CACHE_HOME:-$HOME/.cache}/current_brightness"
CUR="$(cat "$CUR_FILE" 2> /dev/null || echo 50)"

case "${1:0:1}" in
    '')      echo "$CUR"; exit              ;;
    '+'|'-') NEW="$((CUR - CUR % $1 + $1))" ;;
    *)       NEW="$1"                       ;;
esac

for dev in /sys/class/backlight/*; do
    set_brightness "$dev" "$NEW"
done

echo "$NEW" > "$CUR_FILE"

kill -35 "$(cat "$HOME/.cache/pidofbar")"