/**
 * 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) {
                final ConnectedComponent cc = new ConnectedComponent();
                // Flood-fill (node, target-color, replacement-color):
                // 1. Set Q to the empty queue.
                // Queue<Pixel> queue = new LinkedList<Pixel>();
                final LinkedHashSet<Pixel> queue = new LinkedHashSet<Pixel>();

                // 2. If the color of node is not equal to target-color, return.
                final 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();
                        final 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 && output[n.y][n.x] != color) {
                                // 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:
                                        final int north = n.y - 1;
                                        final 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>();

                final 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;
        }
}