/**
 * Copyright (c) 2011, The University of Southampton and the individual contributors.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 *   *  Redistributions of source code must retain the above copyright notice,
 *      this list of conditions and the following disclaimer.
 *
 *   *  Redistributions in binary form must reproduce the above copyright notice,
 *      this list of conditions and the following disclaimer in the documentation
 *      and/or other materials provided with the distribution.
 *
 *   *  Neither the name of the University of Southampton nor the names of its
 *      contributors may be used to endorse or promote products derived from this
 *      software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
 * ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
 * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package org.openimaj.image.connectedcomponent;

import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.List;

import org.openimaj.image.FImage;
import org.openimaj.image.analyser.ImageAnalyser;
import org.openimaj.image.pixel.ConnectedComponent;
import org.openimaj.image.pixel.Pixel;

/**
 * A Connected Component Labeler for grey-level images. This class can be
 * used to transform an image that represents a map of labeled objects
 * into a list of {@link ConnectedComponent}s.  
 * <p>
 * Internally we use a flood-fill approach to finding the {@link ConnectedComponent}s.
 * 
 * @author Jonathon Hare (jsh2@ecs.soton.ac.uk)
 */
public class GreyscaleConnectedComponentLabeler implements ImageAnalyser<FImage> {
        List<ConnectedComponent> components;
        
        /**
         * Syntactic sugar for calling {@link #analyseImage(FImage)} followed by 
         * {@link #getComponents()};
         *  
         * @param image the image to extract components from
         * @return the extracted components.
         */
        public List<ConnectedComponent> findComponents(FImage image) {
                analyseImage(image);
                return components;
        }
        
        protected ConnectedComponent floodFill(FImage image, Pixel start, int[][] output, int color) {
                ConnectedComponent cc = new ConnectedComponent();
//              Flood-fill (node, target-color, replacement-color):
//                       1. Set Q to the empty queue.
                //Queue<Pixel> queue = new LinkedList<Pixel>();
                LinkedHashSet<Pixel> queue = new LinkedHashSet<Pixel>();
                
//                       2. If the color of node is not equal to target-color, return.
                float targetColour = image.pixels[start.y][start.x];
                
//                       3. Add node to Q.
                queue.add(start);
//                       4. For each element n of Q:
                while (queue.size() > 0) {
                        //Pixel n = queue.poll();
                        Pixel n = queue.iterator().next();
                        queue.remove(n);
                        
//                       5.  If the color of n is equal to target-color:
                        if (image.pixels[n.y][n.x] == targetColour) {
//                       6.   Set w and e equal to n.
                                int e = n.x, w=n.x;
//                       7.   Move w to the west until the color of the node to the west of w no longer matches target-color.
                                while (w>0 && image.pixels[n.y][w-1] == targetColour) w--;
                                
//                       8.   Move e to the east until the color of the node to the east of e no longer matches target-color.
                                while (e<image.width-1 && image.pixels[n.y][e+1] == targetColour) e++;
                                
//                       9.   Set the color of nodes between w and e to replacement-color.
                                for (int i=w; i<=e; i++) {
                                        output[n.y][i] = color;
                                        cc.addPixel(i, n.y);
                                        
//                      10.   For each node n between w and e:
                                        int north = n.y - 1;
                                        int south = n.y + 1;
//                      11.    If the color of the node to the north of n is target-color, add that node to Q.
                                        if (north >= 0 && image.pixels[north][i] == targetColour && output[north][i] != color) queue.add(new Pixel(i, north));
//                             If the color of the node to the south of n is target-color, add that node to Q.
                                        if (south < image.height && image.pixels[south][i] == targetColour && output[south][i] != color) queue.add(new Pixel(i, south));
                                }
//                      12. Continue looping until Q is exhausted.
                        }
                }
//                      13. Return.
                return cc;
        }

        @Override
        public void analyseImage(FImage image) {
                components = new ArrayList<ConnectedComponent>();
                
                int [][] labels = new int[image.height][image.width];
                int nextColor=1;
                
                for (int y=0; y<image.height; y++) {
                        for (int x=0; x<image.width; x++) {
                                if (labels[y][x] == 0) {
                                        components.add(floodFill(image, new Pixel(x, y), labels, nextColor));
                                        nextColor++;
                                }
                        }
                }
        }
        
        /**
         * @return the list of components found in the last call to {@link #analyseImage(FImage)}.
         */
        public List<ConnectedComponent> getComponents() {
                return components;
        }
}