#!/usr/bin/env bash

#  dimmer is a script that changes hex color codes to reduce brightness
#  Copyright (C) 2016 Anton Karmanov <starcom24@gmail.com>
#
#  This program is free software: you can redistribute it and/or modify
#  it under the terms of the GNU General Public License as published by
#  the Free Software Foundation, either version 3 of the License, or any
#  later version.
#
#  This program is distributed in the hope that it will be useful,
#  but WITHOUT ANY WARRANTY; without even the implied warranty of
#  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
#  GNU General Public License for more details.
#
#  You should have received a copy of the GNU General Public License
#  along with this program.  If not, see <http://www.gnu.org/licenses/>.

brightness=50

if [ -n "$1" ] ; then
  brightness=$1
fi

shopt -s nocasematch

while read -r line
do

  if
    ! [[ $brightness =~ ^[0-9]+$ ]] || \
      [ "$brightness" -lt 0 ] || \
      [ "$brightness" -gt 100 ]
  then
    >&2 echo "dimmer: Invalid brightness value"
    exit 1
  fi

  if [ ${#line} -eq 7 ] && [ "${line:0:1}" = "#" ] &&\
    [[ ${line:1:6} =~ ^[0-9A-F]{6}$ ]]
  then
    if [ "${brightness}" -eq 0 ]
    then
      # shellcheck disable=SC2016
      line='$000000'
    else
      colors=("0x${line:1:2}" "0x${line:3:2}" "0x${line:5:2}")
      line='#'
      for color in "${colors[@]}"; do
        value=$(((color + (100 / brightness - 1)) * brightness / 100))
        color=$(echo "obase=16; ${value}" | bc)

      # If <= 9 supplement with 0.
      if [ ${#color} -lt 2 ] ; then
        color="0${color}"
      fi

      line="$line$color"
    done
    fi
  fi

  echo "$line"
done