/*
 * Copyright (C) 2009 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.GwtCompatible;
import com.google.common.base.Preconditions;
import com.google.common.collect.ForwardingObject;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

A Future which forwards all its method calls to another future. Subclasses should override one or more methods to modify the behavior of the backing future as desired per the decorator pattern.
Most subclasses can just use SimpleForwardingFuture. 
Author:
Sven Mawson
Since:
1.0/**
 * A {@link Future} which forwards all its method calls to another future. Subclasses should
 * override one or more methods to modify the behavior of the backing future as desired per the <a
 * href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p>Most subclasses can just use {@link SimpleForwardingFuture}.
 *
 * @author Sven Mawson
 * @since 1.0
 */
@CanIgnoreReturnValue // TODO(cpovirk): Consider being more strict.
@GwtCompatible
public abstract class ForwardingFuture<V> extends ForwardingObject implements Future<V> {
  
Constructor for use by subclasses. /** Constructor for use by subclasses. */
  protected ForwardingFuture() {}

  @Override
  protected abstract Future<? extends V> delegate();

  @Override
  public boolean cancel(boolean mayInterruptIfRunning) {
    return delegate().cancel(mayInterruptIfRunning);
  }

  @Override
  public boolean isCancelled() {
    return delegate().isCancelled();
  }

  @Override
  public boolean isDone() {
    return delegate().isDone();
  }

  @Override
  public V get() throws InterruptedException, ExecutionException {
    return delegate().get();
  }

  @Override
  public V get(long timeout, TimeUnit unit)
      throws InterruptedException, ExecutionException, TimeoutException {
    return delegate().get(timeout, unit);
  }

  // TODO(cpovirk): Use standard Javadoc form for SimpleForwarding* class and constructor
  
A simplified version of ForwardingFuture where subclasses can pass in an already constructed Future as the delegate. 
Since:
9.0/**
   * A simplified version of {@link ForwardingFuture} where subclasses can pass in an already
   * constructed {@link Future} as the delegate.
   *
   * @since 9.0
   */
  public abstract static class SimpleForwardingFuture<V> extends ForwardingFuture<V> {
    private final Future<V> delegate;

    protected SimpleForwardingFuture(Future<V> delegate) {
      this.delegate = Preconditions.checkNotNull(delegate);
    }

    @Override
    protected final Future<V> delegate() {
      return delegate;
    }
  }
}