#!/bin/bash -e

function round() {
    local nb="$1"
    local closest="${2#-}"
    local mod; mod="$((nb % closest))"

    if [ "$mod" -lt "$((closest / 2))" ]; then
        echo "$((nb - mod))"
    else
        echo "$((nb + closest - mod))"
    fi
}

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

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

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

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

NOTIFY='notify-send -t 1000 -a changeBrightness -u low'
NOTIFYVOL="$NOTIFY -i audio-volume-high"

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

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

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

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

$NOTIFYVOL -h string:synchronous:vol -h int:value:"$CUR" "$CUR%"