/**
 * Copyright 2009 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 org.waveprotocol.wave.client.scheduler;

import com.google.common.annotations.VisibleForTesting;
import com.google.gwt.user.client.ui.Widget;
import org.waveprotocol.wave.client.scheduler.Scheduler.Priority;

/**
 * Provides a single Scheduler instance for all of the Wave client. This is
 * only a temporary measure while we convert existing classes to use a
 * dependency injected Scheduler.
 *
 */
public class SchedulerInstance {
  private static BrowserBackedScheduler instance;

  private static TimerService low;
  private static TimerService high;
  private static TimerService medium;

  /** Inject a default BrowserBackedScheduler */
  @VisibleForTesting
  public static void setSchedulerInstance(BrowserBackedScheduler instance) {
    SchedulerInstance.instance = instance;
    setDefaultTimerService();
  }

  private static void setDefaultTimerService() {
    low = new SchedulerTimerService(instance, Priority.LOW);
    high = new SchedulerTimerService(instance, Priority.HIGH);
    medium = new SchedulerTimerService(instance, Priority.MEDIUM);
  }

  /** Initialise a default BrowserBackedScheduler if there wasn't one */
  private static void init() {
    if (instance == null) {
      setSchedulerInstance(new BrowserBackedScheduler(GwtSimpleTimer.FACTORY, Controller.NOOP));
    }
  }

  /**
   * @return A shared Scheduler instance.
   */
  public static Scheduler get() {
    init();
    return instance;
  }

  /**
   * @return A shared low-priority timer service based on the scheduler instance.
   */
  public static TimerService getLowPriorityTimer() {
    init();
    return low;
  }

  /**
   * @return A shared high-priority timer service based on the scheduler instance.
   */
  public static TimerService getHighPriorityTimer() {
    init();
    return high;
  }

  /**
   * @return A shared high-priority timer service based on the scheduler instance.
   */
  public static TimerService getMediumPriorityTimer() {
    init();
    return medium;
  }

  /**
   * @return a widget for displaying and controlling the singleton scheduler.
   */
  public static Widget getController() {
    init();
    return instance.getController();
  }
}