#!/bin/bash

# ASUS T100TA screen brightness control script.
#
# This script invokes xrandr to increase or decrease the brightness of
# the screen by applying a software only modification that therefore
# doesn't affect the power consumption. See the xrandr manual for more
# info. This script also uses bc for floating point calculations.
# Please note that Redshift (and possibly other similar applications),
# if it is running, resets the brightness value every time and it
# needs to be disabled.

# Copyright 2017 Francesco De Vita <devfra[at]inventati[dot]org>
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
# implied.  See the License for the specific language governing
# permissions and limitations under the License.


# Min and max screen brigthness, correct values are between 0 and 1.
min_brightness=0.2
max_brightness=1


# Display usage if wrong input arguments are supplied.
if [[ $# -ne 1 ]] || [[ $1 != "decrease" && $1 != "increase" ]]
then
    echo "ASUS T100TA screen brightness control script"
    echo "Usage: $0 [decrease|increase]"
    exit 1
fi


# Check if xrandr and bc are installed.
hash xrandr 2>/dev/null || { echo "xrandr is not installed"; exit 1; }
hash bc 2>/dev/null || { echo "bc is not installed"; exit 1; }


# Xrandr output for the screen, supposing no external screen attached.
screen_output=$(xrandr | grep -w connected | cut -d" " -f1)

# Current brightness.
brightness=$(xrandr --current --verbose | grep Bright | cut -d" " -f2)


# Decrease or increase the screen brightness.
case $1 in
    decrease)
        if [[ $(echo "$brightness>$min_brightness" | bc) -eq 1 ]]
        then
            brightness=$(echo "$brightness-0.2" | bc)
            xrandr --output $screen_output --brightness $brightness
        fi
        ;;
    increase)
        if [[ $(echo "$brightness<$max_brightness" | bc) -eq 1 ]]
        then
            brightness=$(echo "$brightness+0.2" | bc)
            xrandr --output $screen_output --brightness $brightness
        fi
        ;;
esac

exit 0