//
//  ========================================================================
//  Copyright (c) 1995-2013 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
//
//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
//

package org.eclipse.jetty.util;

import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.nio.channels.UnresolvedAddressException;
import java.util.concurrent.Executor;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TimeoutException;
import java.util.concurrent.atomic.AtomicBoolean;

import org.eclipse.jetty.util.log.Log;
import org.eclipse.jetty.util.log.Logger;
import org.eclipse.jetty.util.thread.Scheduler;

/**
 * Creates asynchronously {@link SocketAddress} instances, returning them through a {@link Promise},
 * in order to avoid blocking on DNS lookup.
 * <p />
 * {@link InetSocketAddress#InetSocketAddress(String, int)} attempts to perform a DNS resolution of
 * the host name, and this may block for several seconds.
 * This class creates the {@link InetSocketAddress} in a separate thread and provides the result
 * through a {@link Promise}, with the possibility to specify a timeout for the operation.
 * <p />
 * Example usage:
 * <pre>
 * SocketAddressResolver resolver = new SocketAddressResolver(executor, scheduler);
 * resolver.resolve("www.google.com", 80, new Promise&lt;SocketAddress&gt;()
 * {
 *     public void succeeded(SocketAddress result)
 *     {
 *         // The address was resolved
 *     }
 *
 *     public void failed(Throwable failure)
 *     {
 *         // The address resolution failed
 *     }
 * });
 * </pre>
 */
public class SocketAddressResolver
{
    private static final Logger LOG = Log.getLogger(SocketAddressResolver.class);

    private final Executor executor;
    private final Scheduler scheduler;
    private final long timeout;

    /**
     * Creates a new instance with the given executor (to perform DNS resolution in a separate thread),
     * the given scheduler (to cancel the operation if it takes too long) and the given timeout, in milliseconds.
     *
     * @param executor the thread pool to use to perform DNS resolution in pooled threads
     * @param scheduler the scheduler to schedule tasks to cancel DNS resolution if it takes too long
     * @param timeout the timeout, in milliseconds, for the DNS resolution to complete
     */
    public SocketAddressResolver(Executor executor, Scheduler scheduler, long timeout)
    {
        this.executor = executor;
        this.scheduler = scheduler;
        this.timeout = timeout;
    }

    public Executor getExecutor()
    {
        return executor;
    }

    public Scheduler getScheduler()
    {
        return scheduler;
    }

    public long getTimeout()
    {
        return timeout;
    }

    /**
     * Resolves the given host and port, returning a {@link SocketAddress} through the given {@link Promise}
     * with the default timeout.
     *
     * @param host the host to resolve
     * @param port the port of the resulting socket address
     * @param promise the callback invoked when the resolution succeeds or fails
     * @see #resolve(String, int, long, Promise)
     */
    public void resolve(String host, int port, Promise<SocketAddress> promise)
    {
        resolve(host, port, timeout, promise);
    }

    /**
     * Resolves the given host and port, returning a {@link SocketAddress} through the given {@link Promise}
     * with the given timeout.
     *
     * @param host the host to resolve
     * @param port the port of the resulting socket address
     * @param timeout the timeout, in milliseconds, for the DNS resolution to complete
     * @param promise the callback invoked when the resolution succeeds or fails
     */
    protected void resolve(final String host, final int port, final long timeout, final Promise<SocketAddress> promise)
    {
        executor.execute(new Runnable()
        {
            @Override
            public void run()
            {
                Scheduler.Task task = null;
                final AtomicBoolean complete = new AtomicBoolean();
                if (timeout > 0)
                {
                    final Thread thread = Thread.currentThread();
                    task = scheduler.schedule(new Runnable()
                    {
                        @Override
                        public void run()
                        {
                            if (complete.compareAndSet(false, true))
                            {
                                promise.failed(new TimeoutException());
                                thread.interrupt();
                            }
                        }
                    }, timeout, TimeUnit.MILLISECONDS);
                }

                try
                {
                    long start = System.nanoTime();
                    InetSocketAddress result = new InetSocketAddress(host, port);
                    long elapsed = System.nanoTime() - start;
                    LOG.debug("Resolved {} in {} ms", host, TimeUnit.NANOSECONDS.toMillis(elapsed));
                    if (complete.compareAndSet(false, true))
                    {
                        if (result.isUnresolved())
                            promise.failed(new UnresolvedAddressException());
                        else
                            promise.succeeded(result);
                    }
                }
                catch (Throwable x)
                {
                    if (complete.compareAndSet(false, true))
                        promise.failed(x);
                }
                finally
                {
                    if (task != null)
                        task.cancel();
                    // Reset the interrupted status before releasing the thread to the pool
                    Thread.interrupted();
                }
            }
        });
    }
}
