/*
 * Copyright (C) 2008 The Guava Authors
 *
 * 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.common.util.concurrent;

import com.google.common.annotations.GwtIncompatible;

import java.util.concurrent.Callable;
import java.util.concurrent.Executor;
import java.util.concurrent.FutureTask;

import javax.annotation.Nullable;

/**
 * A {@link FutureTask} that also implements the {@link ListenableFuture} interface. Unlike 
 * {@code FutureTask}, {@code ListenableFutureTask} does not provide an overrideable {@link
 * FutureTask#done() done()} method. For similar functionality, call {@link #addListener}.
 *
 * <p>Few users should use this class. It is intended primarily for those who are implementing an
 * {@code ExecutorService}. Most users should call {@link ListeningExecutorService#submit(Callable)
 * ListeningExecutorService.submit} on a service obtained from {@link
 * MoreExecutors#listeningDecorator}.
 *
 * @author Sven Mawson
 * @since 1.0
 */
@GwtIncompatible
public class ListenableFutureTask<V> extends FutureTask<V> implements ListenableFuture<V> {
  // TODO(cpovirk): explore ways of making ListenableFutureTask final. There are some valid reasons
  // such as BoundedQueueExecutorService to allow extends but it would be nice to make it final to
  // avoid unintended usage.

  // The execution list to hold our listeners.
  private final ExecutionList executionList = new ExecutionList();

  /**
   * Creates a {@code ListenableFutureTask} that will upon running, execute the given {@code
   * Callable}.
   *
   * @param callable the callable task
   * @since 10.0
   */
  public static <V> ListenableFutureTask<V> create(Callable<V> callable) {
    return new ListenableFutureTask<V>(callable);
  }

  /**
   * Creates a {@code ListenableFutureTask} that will upon running, execute the given {@code
   * Runnable}, and arrange that {@code get} will return the given result on successful completion.
   *
   * @param runnable the runnable task
   * @param result the result to return on successful completion. If you don't need a particular
   *     result, consider using constructions of the form: {@code ListenableFuture<?> f =
   *     ListenableFutureTask.create(runnable, null)}
   * @since 10.0
   */
  public static <V> ListenableFutureTask<V> create(Runnable runnable, @Nullable V result) {
    return new ListenableFutureTask<V>(runnable, result);
  }

  ListenableFutureTask(Callable<V> callable) {
    super(callable);
  }

  ListenableFutureTask(Runnable runnable, @Nullable V result) {
    super(runnable, result);
  }

  @Override
  public void addListener(Runnable listener, Executor exec) {
    executionList.add(listener, exec);
  }

  /**
   * Internal implementation detail used to invoke the listeners.
   */
  @Override
  protected void done() {
    executionList.execute();
  }
}
