#!/bin/bash -e

function get_current() {
    local cur; cur="$(cat "$1/brightness")"
    local max; max="$(cat "$1/max_brightness")"

    echo "$((cur * 100 / max))"
}

function set_light() {
    local max; max="$(cat "$1/max_brightness")"

    echo "$((CUR * max / 100))" > "$1/brightness"
}


DIRS=(/sys/class/backlight/*)
CUR="$(get_current "${DIRS[0]}")"

echo "$CUR"
echo "\$(($CUR + $1 - $CUR % $1 + $CUR % $1 / $1 * $1))"
case "${1:0:1}" in
    '')      echo "$CUR"; exit ;;
    '+'|'-') CUR="$(($CUR + $1 - $CUR % $1 + $CUR % $1 * 10 / $1 / 5 * $1))" ;;
    *)       CUR="$1" ;;
esac
echo "$CUR"

[ "$CUR" -lt   0 ] && CUR=0
[ "$CUR" -gt 100 ] && CUR=100

for d in "${DIRS[@]}"; do
    set_light "$d"
done

notify-send -t 1000 -u low -i display-brightness-symbolic \
    -h string:synchronous:light -h int:value:"$CUR" "$CUR%"