// Copyright 2012 Google Inc. All Rights Reserved.
//
// 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 com.google.collide.client.util;

import com.google.collide.client.bootstrap.BootstrapSession;
import com.google.gwt.core.client.JavaScriptObject;

import elemental.events.EventListener;
import elemental.html.Document.Event;
import elemental.js.events.JsEvent;

/*
 * TODO: Make a scheduler so there's only one event listener for
 * ALL things that want to asyncrun
 */
/**
 * An utility class to execute some logic asynchronously as soon as possible.
 *
 */
public abstract class AsyncRunner implements Runnable {

  private static final String EVENT_MESSAGE = "message";

  private static class MessageEvent extends JsEvent implements Event {
    protected MessageEvent() {
    }

    public final native Object getData() /*-{
      return this.data;
    }-*/;

    public final native JavaScriptObject getSource() /*-{
      return this.source;
    }-*/;
  }

  private static int instanceId = 0;

  private final String messageName =
      BootstrapSession.getBootstrapSession().getActiveClientId() + ":AsyncRunner." + instanceId++;
  private final String targetOrigin = Elements.getDocument().getLocation().getProtocol() + "//"
      + Elements.getDocument().getLocation().getHost();

  private boolean isCancelled;
  private boolean isAttached = false;

  private EventListener messageHandler = new EventListener() {
    @Override
    public void handleEvent(elemental.events.Event rawEvent) {
      MessageEvent event = (MessageEvent) rawEvent;
      if (!isCancelled && event.getData().equals(messageName)) {
        detachMessageHandler();
        event.stopPropagation();
        run();
      }
    }
  };

  public AsyncRunner() {
  }

  public void cancel() {
    isCancelled = true;
    detachMessageHandler();
  }

  public void schedule() {
    isCancelled = false;
    attachMessageHandler();
    scheduleJs();
  }

  private void attachMessageHandler() {
    if (!isAttached) {
      Elements.getWindow().addEventListener(EVENT_MESSAGE, messageHandler, true);
      isAttached = true;
    }
  }

  private void detachMessageHandler() {
    if (isAttached) {
      Elements.getWindow().removeEventListener(EVENT_MESSAGE, messageHandler, true);
      isAttached = false;
    }
  }

  private native void scheduleJs() /*-{
    // This is more responsive than setTimeout(0)
    $wnd.postMessage(this.@com.google.collide.client.util.AsyncRunner::messageName, this.
        @com.google.collide.client.util.AsyncRunner::targetOrigin);
  }-*/;
}