/**********************************************
    * Copyright (C) 2011 Lukas Laag
    * This file is part of svgreal.
    * 
    * svgreal 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
    * (at your option) any later version.
    * 
   * svgreal 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 svgreal.  If not, see http://www.gnu.org/licenses/
   **********************************************/
  package org.vectomatic.svg.edit.client.utils;
  
  import java.util.ArrayList;
  import java.util.HashMap;
  import java.util.List;
  import java.util.Map;
  
  import org.vectomatic.svg.edit.client.SvgrealApp;
  
  import com.google.gwt.event.dom.client.LoadEvent;
  import com.google.gwt.event.dom.client.LoadHandler;
  import com.google.gwt.event.logical.shared.HasInitializeHandlers;
  import com.google.gwt.event.logical.shared.InitializeEvent;
  import com.google.gwt.event.logical.shared.InitializeHandler;
  import com.google.gwt.event.shared.GwtEvent;
  import com.google.gwt.event.shared.HandlerRegistration;
  import com.google.gwt.resources.client.ImageResource;
  
  /**
   * Class to preload a list of images
   * @author laaglu
   */
  public class ImageLoader implements HasInitializeHandlers {
  	protected List<SimpleImage> images;
  	protected ImageResource[] resources;
  	
  	/**
  	 * Constructor
  	 */
  	public ImageLoader() {			
  		images = new ArrayList<SimpleImage>();
  		resources = new ImageResource[0];
  	}
  	
  	/**
  	 * Preloads the specified images, asynchronously. Once loaded, a
  	 * {@link com.google.gwt.event.dom.client.LoadEvent} is fired.
  	 * @param resources
  	 * The images to preload.
  	 */
  	public void loadImages(ImageResource[] resources) {
  		images.clear();
  		this.resources = resources;
  		readNext();
  	}
  	
  	private void readNext() {
  		if (images.size() < resources.length) {
  			final SimpleImage image = new SimpleImage();
  			images.add(image);
  			image.addLoadHandler(new LoadHandler() {
  				@Override
  				public void onLoad(LoadEvent event) {
  					readNext();
  				}
  			});
  			image.setSrc(resources[images.size() - 1].getSafeUri().asString());
  		} else {
  			InitializeEvent.fire(this);
  		}
  	}
  
  	/**
  	 * Returns the preloaded images.
  	 * @return the preloaded images.
  	 * @throws IllegalStateException if this method is
  	 * invoked synchronously before the 
  	 * {@link com.google.gwt.event.dom.client.LoadEvent} has been fired.
  	 */
  	public Map<ImageResource, SimpleImage> getImages() {
  		if (resources.length != images.size()) {
  			throw new IllegalStateException();
  		}
  		Map<ImageResource, SimpleImage> resourceToImage = new HashMap<ImageResource, SimpleImage>();
  		for (int i = 0; i < resources.length; i++) {
  			resourceToImage.put(resources[i], images.get(i));
  		}
  		return resourceToImage;
  	}
  	
  	@Override
  	public void fireEvent(GwtEvent<?> event) {
 		SvgrealApp.getApp().getEventBus().fireEventFromSource(event, this);
 		
 	}
 
 	@Override
 	public HandlerRegistration addInitializeHandler(InitializeHandler handler) {
 		return SvgrealApp.getApp().getEventBus().addHandlerToSource(InitializeEvent.getType(), this, handler);
 	}	
 }