/*
 * Copyright (C) 2011 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 static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.Throwables;
import com.google.common.collect.ImmutableList;

import java.util.Collection;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;

/**
 * An abstract {@code ExecutorService} that allows subclasses to
 * {@linkplain #wrapTask(Callable) wrap} tasks before they are submitted
 * to the underlying executor.
 *
 * <p>Note that task wrapping may occur even if the task is never executed.
 *
 * <p>For delegation without task-wrapping, see
 * {@link ForwardingExecutorService}.
 *
 * @author Chris Nokleberg
 */
abstract class WrappingExecutorService implements ExecutorService {
  private final ExecutorService delegate;

  protected WrappingExecutorService(ExecutorService delegate) {
    this.delegate = checkNotNull(delegate);
  }

  /**
   * Wraps a {@code Callable} for submission to the underlying executor. This
   * method is also applied to any {@code Runnable} passed to the default
   * implementation of {@link #wrapTest(Runnable)}.
   */
  protected abstract <T> Callable<T> wrapTask(Callable<T> callable);

  /**
   * Wraps a {@code Runnable} for submission to the underlying executor. The
   * default implementation delegates to {@link #wrapTask(Callable)}.
   */
  protected Runnable wrapTask(Runnable command) {
    final Callable<Object> wrapped = wrapTask(
        Executors.callable(command, null));
    return new Runnable() {
      @Override public void run() {
        try {
          wrapped.call();
        } catch (Exception e) {
          Throwables.propagate(e);
        }
      }
    };
  }

  /**
   * Wraps a collection of tasks.
   *
   * @throws NullPointerException if any element of {@code tasks} is null
   */
  private final <T> ImmutableList<Callable<T>> wrapTasks(
      Collection<? extends Callable<T>> tasks) {
    ImmutableList.Builder<Callable<T>> builder = ImmutableList.builder();
    for (Callable<T> task : tasks) {
      builder.add(wrapTask(task));
    }
    return builder.build();
  }

  // These methods wrap before delegating.
  @Override
  public final void execute(Runnable command) {
    delegate.execute(wrapTask(command));
  }

  @Override
  public final <T> Future<T> submit(Callable<T> task) {
    return delegate.submit(wrapTask(checkNotNull(task)));
  }

  @Override
  public final Future<?> submit(Runnable task) {
    return delegate.submit(wrapTask(task));
  }

  @Override
  public final <T> Future<T> submit(Runnable task, T result) {
    return delegate.submit(wrapTask(task), result);
  }

  @Override
  public final <T> List<Future<T>> invokeAll(
      Collection<? extends Callable<T>> tasks) throws InterruptedException {
    return delegate.invokeAll(wrapTasks(tasks));
  }

  @Override
  public final <T> List<Future<T>> invokeAll(
      Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
      throws InterruptedException {
    return delegate.invokeAll(wrapTasks(tasks), timeout, unit);
  }

  @Override
  public final <T> T invokeAny(Collection<? extends Callable<T>> tasks)
      throws InterruptedException, ExecutionException {
    return delegate.invokeAny(wrapTasks(tasks));
  }

  @Override
  public final <T> T invokeAny(
      Collection<? extends Callable<T>> tasks, long timeout, TimeUnit unit)
      throws InterruptedException, ExecutionException, TimeoutException {
    return delegate.invokeAny(wrapTasks(tasks), timeout, unit);
  }

  // The remaining methods just delegate.

  @Override
  public final void shutdown() {
    delegate.shutdown();
  }

  @Override
  public final List<Runnable> shutdownNow() {
    return delegate.shutdownNow();
  }

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

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

  @Override
  public final boolean awaitTermination(long timeout, TimeUnit unit)
      throws InterruptedException {
    return delegate.awaitTermination(timeout, unit);
  }
}
