#!/bin/bash

if [ "$(id -u)" != "0" ]; then
    exec sudo "$0" "$@"
fi;

MAX=$(cat /sys/class/backlight/intel_backlight/max_brightness)
CURRENT=$(cat /sys/class/backlight/intel_backlight/brightness)
NEW=$CURRENT
ADJ=$(( $MAX  / ${2:-20} ))

if [ "$1" == "max" ]; then
    NEW=$MAX
elif [ "$1" == "off" ]; then
    NEW=0
elif [ "$1" == "min" ]; then
    NEW=1
elif [ "$1" == "dec" ]; then
    NEW=$(( $CURRENT - $ADJ  < 1 ? 1 : $CURRENT - $ADJ ))
elif echo "$1" | grep -q '^[[:digit:]][[:digit:]]*\%*$'; then
    NEW=$(( $(echo "$1" | sed 's/\%//') * $MAX / 100 ))
else
    NEW=$(( $CURRENT + $ADJ  >= $MAX ? $MAX : $CURRENT + $ADJ ))
fi

echo $NEW > /sys/class/backlight/intel_backlight/brightness