ChannelFactory.java

// $codepro.audit.disable disallowNativeMethods
/*
 * Copyright (C) 2011 Google Inc. Licensed 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 net.thesocialos.client.channelApi;

import com.google.gwt.dom.client.Document;
import com.google.gwt.dom.client.ScriptElement;
import com.google.gwt.user.client.Timer;

/** Manages creating {@link Channel}s to receive messages from the server. */
public class ChannelFactory {
	
	private static final String CHANNEL_SRC = "/_ah/channel/jsapi";
	private static Channel channel;
	
	/**
	 * Creates a {@link Channel} with the given client ID, passing it to the given {@link ChannelCreatedCallback}.
	 * 
	 * <p>
	 * If a Channel has already been created, this will immediately be passed to the callback, so only one Channel will
	 * ever be created by this method.
	 * </p>
	 */
	public static void createChannel(final String clientId, final ChannelCreatedCallback callback) {
		if (channel == null) {
			ScriptElement script = Document.get().createScriptElement();
			script.setSrc(CHANNEL_SRC);
			Document.get().getElementsByTagName("head").getItem(0).appendChild(script);
			
			new Timer() {
				@Override
				public void run() {
					if (scriptLoaded()) {
						channel = createChannelImpl(clientId);
						callback.onChannelCreated(channel);
						cancel();
					}
				}
			}.scheduleRepeating(100);
		} else
			callback.onChannelCreated(channel);
	}
	
	public static void deleteChannel() {
		channel = null;
	}
	
	private static native boolean scriptLoaded() /*-{
		return !!$wnd.goog && !!$wnd.goog.appengine
				&& !!$wnd.goog.appengine.Channel;
	}-*/;
	
	private static final native Channel createChannelImpl(String clientId) /*-{
		return new $wnd.goog.appengine.Channel(clientId);
	}-*/;
	
	public interface ChannelCreatedCallback {
		public void onChannelCreated(Channel channel);
	}
}