#!/bin/bash
# Script to set backlight on startup on Lenovo W540 using
# /sys/class/backlight/intel_backlight/brightness
# This must be run as root.

# check if root
if [[ $EUID -ne 0 ]];then
  echo "This must be run as root."
else
  # get current and maximum brightness, set maximum steps allowed
  brightness_current=$(cat /sys/class/backlight/intel_backlight/brightness)
  brightness_max=$(cat /sys/class/backlight/intel_backlight/max_brightness)
  brightness_max=$(($brightness_max-1000))
  brightness_steps=20
  brightness_steps_width=$(($brightness_max/$brightness_steps))
  brightness_new=0
  # if first parameter to this script is a number
  re='^[0-9]+$'
  if [[ $1 =~ $re ]]; then
    echo "Direct step called"
    if [[ $1 -gt brightness_steps && $1 -ne 0 ]];then
      brightness_new=$(($1*brightness_steps_width))
    fi
  elif [[ $1 == "up" || $1 == "down" ]];then
    brightness_calc=$(($brightness_current / $brightness_steps_width))
    case $1 in
      "up" )
        brightness_calc=$((($brightness_calc+1) * $brightness_steps_width))
        echo "brightness_calc: $brightness_calc"
        echo "brightness_max: $brightness_max"
        if [[ $brightness_max -gt $brightness_calc ]];then
          echo "true"
          brightness_new=$brightness_calc
        else
          echo "false"
          brightness_new=$brightness_current
        fi
        ;;
      "down" )
        brightness_calc=$((($brightness_calc-1) * $brightness_steps_width))
        echo "brightness_calc: $brightness_calc"
        if [[ $brightness_calc -gt 0 ]];then
          brightness_new=$brightness_calc
        else
          brightness_new=$brightness_current
        fi
        ;;
    esac
    echo "Step called with: $1"
  fi
  echo $brightness_current
  echo $brightness_new
  # set to 234 (around 4th step)
  #echo 234 > /sys/class/backlight/intel_backlight/brightness
  echo $brightness_new > /sys/class/backlight/intel_backlight/brightness
fi