#!/usr/bin/env bash
# set backlight through sysfs

set -euo pipefail

# brightness steps in percentage
brightness_step_size=5
brightness_device=/sys/class/backlight/intel_backlight/brightness
brightness_max_device=/sys/class/backlight/intel_backlight/max_brightness
calculated_brightness=0
amount=0

brightness_steps=$(echo "100/${brightness_step_size}" |bc -l)
maximum_brightness_raw=$(cat $brightness_max_device)
current_brightness_raw=$(cat $brightness_device)
brightness_one_percent_raw=$(echo "${maximum_brightness_raw}/100" |bc -l)
current_brightness_percentage=$(echo "${current_brightness_raw}/(${maximum_brightness_raw}/100)" |bc -l)
current_brightness_remainder=$(echo "${current_brightness_percentage}%${brightness_step_size}"|bc -l)
current_step=$(echo ${current_brightness_percentage}/${brightness_step_size}|bc -l)

check_if_number() {
  if [[ $1 =~ ^[!\-0-9]+$ ]]; then
    echo "Not an Integer: $1"
    exit 1
  fi
}

calculate_increment() {
  check_if_number $1
  if [ $1 -eq 0 ]; then
    echo "There's nothing to do."
    exit 1
  fi
  if [ $1 -gt 0 ]; then
    if [ $(printf '%.0f' $current_brightness_percentage) -eq 100 ]; then
      echo "Already at 100%"
      exit 0
    elif [ $(printf '%.0f' $(echo "${current_brightness_percentage}+$1"| bc)) -gt 100 ]; then
      calculated_brightness=100
    else
      calculated_brightness=$(printf '%.0f' $(echo "${current_brightness_percentage}+$1"| bc))
    fi
  else
    if [ $(printf '%.0f' $current_brightness_percentage) -eq 0 ]; then
      echo "Already at 0%"
      exit 0
    elif [ $(printf '%.0f' $(echo "${current_brightness_percentage}+$1"| bc)) -lt 0 ]; then
      calculated_brightness=0
    else
      calculated_brightness=$(printf '%.0f' $(echo "${current_brightness_percentage}+$1"| bc))
    fi
  fi
}

calculate_percentage() {
  check_if_number $1
  if [ $1 -lt 0 ] || [ $1 -gt 100 ]; then
    echo "Invalid range: $1"
    exit 1
  fi
  calculated_brightness=$1
}

percentage_to_raw() {
  printf '%.0f' $(echo "$1*${brightness_one_percent_raw}"|bc -l)
}

set_brightness() {
  echo "$(percentage_to_raw $calculated_brightness)" > $brightness_device
}

print_help() {
  echo -e "Usage:\n $0 -d <decrement_by_x_percent> \n or $0 -i <increment_by_x_percent>"
  exit 1
}

if [ ${#@} -gt 0 ]; then
  while getopts 'hi:s:' flag; do
    case "${flag}" in
      h)
        print_help
        ;;
      i)
        calculate_increment $OPTARG
          ;;
      s)
        calculate_percentage $OPTARG
        ;;
      *)
        echo "Error! Try '${0} -h'."
        exit 1
        ;;
    esac
  done
else
  print_help
fi

set_brightness