/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You under the Apache License, Version 2.0
    * (the "License"); you may not use this file except in compliance with
    * the License.  You may obtain a copy of the License at
    *
    *      http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  package org.apache.commons.imaging.palette;
  
  import java.awt.image.BufferedImage;
  
  import org.apache.commons.imaging.ImagingException;
  
  /**
   * Dithering algorithms to use when quantizing an image to palette form.
   */
  public final class Dithering {
      private static int adjustPixel(final int argb, final int errA, final int errR, final int errG, final int errB, final int mul) {
          int a = argb >> 24 & 0xff;
          int r = argb >> 16 & 0xff;
          int g = argb >> 8 & 0xff;
          int b = argb & 0xff;
  
          a += errA * mul / 16;
          r += errR * mul / 16;
          g += errG * mul / 16;
          b += errB * mul / 16;
  
          if (a < 0) {
              a = 0;
          } else if (a > 0xff) {
              a = 0xff;
          }
          if (r < 0) {
              r = 0;
          } else if (r > 0xff) {
              r = 0xff;
          }
          if (g < 0) {
              g = 0;
          } else if (g > 0xff) {
              g = 0xff;
          }
          if (b < 0) {
              b = 0;
          } else if (b > 0xff) {
              b = 0xff;
          }
  
          return a << 24 | r << 16 | g << 8 | b;
      }
  
      /**
       * Changes the given image to only use colors from the given palette, applying Floyd-Steinberg dithering in the process. Ensure that your alpha values in
       * the image and in the palette are consistent.
       *
       * @param image   the image to change
       * @param palette the palette to use
       * @throws ImagingException if it fails to read the palette index
       */
      public static void applyFloydSteinbergDithering(final BufferedImage image, final Palette palette) throws ImagingException {
          for (int y = 0; y < image.getHeight(); y++) {
              for (int x = 0; x < image.getWidth(); x++) {
                  final int argb = image.getRGB(x, y);
                  final int index = palette.getPaletteIndex(argb);
                  final int nextArgb = palette.getEntry(index);
                  image.setRGB(x, y, nextArgb);
  
                  final int a = argb >> 24 & 0xff;
                  final int r = argb >> 16 & 0xff;
                  final int g = argb >> 8 & 0xff;
                  final int b = argb & 0xff;
  
                  final int na = nextArgb >> 24 & 0xff;
                  final int nr = nextArgb >> 16 & 0xff;
                  final int ng = nextArgb >> 8 & 0xff;
                  final int nb = nextArgb & 0xff;
  
                  final int errA = a - na;
                  final int errR = r - nr;
                  final int errG = g - ng;
                  final int errB = b - nb;
  
                  if (x + 1 < image.getWidth()) {
                      int update = adjustPixel(image.getRGB(x + 1, y), errA, errR, errG, errB, 7);
                      image.setRGB(x + 1, y, update);
                      if (y + 1 < image.getHeight()) {
                          update = adjustPixel(image.getRGB(x + 1, y + 1), errA, errR, errG, errB, 1);
                          image.setRGB(x + 1, y + 1, update);
                      }
                 }
                 if (y + 1 < image.getHeight()) {
                     int update = adjustPixel(image.getRGB(x, y + 1), errA, errR, errG, errB, 5);
                     image.setRGB(x, y + 1, update);
                     if (x - 1 >= 0) {
                         update = adjustPixel(image.getRGB(x - 1, y + 1), errA, errR, errG, errB, 3);
                         image.setRGB(x - 1, y + 1, update);
                     }
 
                 }
             }
         }
     }
 
     private Dithering() {
         // no instances.
     }
 }