#!/bin/sh

BACKLIGHT="/sys/class/backlight/amdgpu_bl0"

current_brightness=$(cat "$BACKLIGHT/brightness")
max_brightness=$(cat "$BACKLIGHT/max_brightness")

if [ "$#" = "0" ]; then
	echo "$current_brightness"
	exit 0
fi

val="$1"
fc=$(echo "$1" | cut -c1-1)
if [ "$fc" = "+" ] || [ "$fc" = "-" ]; then
	mode="$fc"
	val=$(echo "$1" | cut -c2-)
fi

fc=$(echo "$val" | cut -c1-1)
if [ "$fc" = "%" ]; then
	percentage=$(echo "$val" | cut -c2-)
	val=$(("$max_brightness" * "$percentage"))	
	val=$(("$val" / "100"))
fi

delta="0"
if [ -z "$mode" ]; then
	delta=$(("$val" - "$current_brightness"))
else
	delta="$mode$val"
fi

# Just apply the delta for now, might want to smooth it out later
target_brightness=$(("$current_brightness" + "$delta"))

# Clamp
if [ "$target_brightness" -gt "$max_brightness" ]; then
	target_brightness="$max_brightness"
elif [ "$target_brightness" -lt "0" ]; then
	target_brightness="0"
fi

echo "$target_brightness" > "$BACKLIGHT/brightness"