/*
 * Copyright (c) 2014 Brocade Communications Systems, Inc. and others.  All rights reserved.
 *
 * This program and the accompanying materials are made available under the
 * terms of the Eclipse Public License v1.0 which accompanies this distribution,
 * and is available at http://www.eclipse.org/legal/epl-v10.html
 */

package org.opendaylight.yangtools.util.concurrent;

import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.TimeUnit;

import javax.annotation.Nullable;

import com.google.common.base.MoreObjects;
import com.google.common.base.MoreObjects.ToStringHelper;
import com.google.common.base.Preconditions;
import com.google.common.util.concurrent.AbstractListeningExecutorService;
import com.google.common.util.concurrent.ListenableFuture;

/**
 * An {@link com.google.common.util.concurrent.ListeningExecutorService} implementation that also allows for an {@link Executor} to be
 * specified on construction that is used to execute {@link ListenableFuture} callback Runnables,
 * registered via {@link com.google.common.util.concurrent.Futures#addCallback} or {@link ListenableFuture#addListener} directly,
 * asynchronously when a task that is run on this executor completes. This is useful when you want
 * to guarantee listener callback executions are off-loaded onto another thread to avoid blocking
 * the thread that completed the task, as a common use case is to pass an executor that runs tasks
 * in the same thread as the caller (ie <code>MoreExecutors#sameThreadExecutor</code>}) to
 * {@link ListenableFuture#addListener}.
 * <p>
 * Most commonly, this class would be used in lieu of <code>MoreExecutors#listeningDecorator</code>
 * when the underlying delegate Executor is single-threaded, in which case, you may not want
 * ListenableFuture callbacks to block the single thread.
 * <p>
 * Note: the Executor specified on construction does not replace the Executor specified in
 * {@link ListenableFuture#addListener}. The latter Executor is still used however, if it is
 * detected that the listener Runnable would execute in the thread that completed the task, the
 * listener is executed on Executor specified on construction.
 *
 * @author Thomas Pantelis
 * @see AsyncNotifyingListenableFutureTask
 */
public class AsyncNotifyingListeningExecutorService extends AbstractListeningExecutorService {

    private final ExecutorService delegate;
    private final Executor listenableFutureExecutor;

    /**
     * Constructor.
     *
     * @param delegate the back-end ExecutorService.
     * @param listenableFutureExecutor the executor used to run listener callbacks asynchronously.
     *     If null, no executor is used.
     */
    public AsyncNotifyingListeningExecutorService( ExecutorService delegate,
            @Nullable Executor listenableFutureExecutor ) {
        this.delegate = Preconditions.checkNotNull( delegate );
        this.listenableFutureExecutor = listenableFutureExecutor;
    }

    /**
     * Creates an {@link AsyncNotifyingListenableFutureTask} instance with the listener Executor.
     *
     * @param task the Callable to execute
     */
    private <T> AsyncNotifyingListenableFutureTask<T> newFutureTask( Callable<T> task ) {
        return AsyncNotifyingListenableFutureTask.create( task, listenableFutureExecutor );
    }

    /**
     * Creates an {@link AsyncNotifyingListenableFutureTask} instance with the listener Executor.
     *
     * @param task the Runnable to execute
     */
    private <T> AsyncNotifyingListenableFutureTask<T> newFutureTask( Runnable task, T result ) {
        return AsyncNotifyingListenableFutureTask.create( task, result, listenableFutureExecutor );
    }

    /**
     * Returns the delegate ExecutorService.
     */
    protected ExecutorService getDelegate() {
        return delegate;
    }

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

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

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

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

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

    @Override
    public void execute( Runnable command ) {
        delegate.execute( command );
    }

    @Override
    public <T> ListenableFuture<T> submit( Callable<T> task ) {
        AsyncNotifyingListenableFutureTask<T> futureTask = newFutureTask( task );
        delegate.execute( futureTask );
        return futureTask;
    }

    @Override
    public ListenableFuture<?> submit( Runnable task ) {
        AsyncNotifyingListenableFutureTask<Void> futureTask = newFutureTask( task, null );
        delegate.execute( futureTask );
        return futureTask;
    }

    @Override
    public <T> ListenableFuture<T> submit( Runnable task, T result ) {
        AsyncNotifyingListenableFutureTask<T> futureTask = newFutureTask( task, result );
        delegate.execute( futureTask );
        return futureTask;
    }

    protected ToStringHelper addToStringAttributes( ToStringHelper toStringHelper ) {
        return toStringHelper;
    }

    @Override
    public final String toString(){
        return addToStringAttributes( MoreObjects.toStringHelper( this )
                .add( "delegate", delegate ) ).toString();
    }
}