#!/bin/sh

xrandr_verbose=$(xrandr --verbose)
monitors=$(echo "$xrandr_verbose" | grep -i '\sconnected' | grep '[0-9]x[0-9]' | cut -d ' ' -f1)

for monitor in $monitors; do
  case "$monitor" in
  *DP* | *DisplayPort* | *HDMI*)
    current_brightness=$(echo "$xrandr_verbose" | grep -i "^$monitor connected" -A5 | grep -i "Brightness:" | cut -d ' ' -f2)
    [ -z "$current_brightness" ] && continue
    if [ "$#" -eq 2 ]; then
      scale_change=$(echo "$2 / 100" | bc -l)
      case "$1" in
      "-inc") new_brightness=$(echo "$current_brightness + $scale_change" | bc -l) ;;
      "-dec") new_brightness=$(echo "$current_brightness - $scale_change" | bc -l) ;;
      *) echo "Invalid argument $1. Use -inc or -dec." && exit 1 ;;
      esac
      new_brightness=$(echo "if ($new_brightness > 1) 1 else if ($new_brightness < 0) 0 else $new_brightness" | bc -l)
      xrandr --output "$monitor" --brightness "$new_brightness"
    fi
    ;;
  esac
done