//
   //  ========================================================================
   //  Copyright (c) 1995-2016 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.InetAddress;
  import java.net.InetSocketAddress;
  import java.net.SocketAddress;
  import java.net.UnknownHostException;
  import java.util.ArrayList;
  import java.util.List;
  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.annotation.ManagedAttribute;
  import org.eclipse.jetty.util.annotation.ManagedObject;
  import org.eclipse.jetty.util.log.Log;
  import org.eclipse.jetty.util.log.Logger;
  import org.eclipse.jetty.util.thread.Scheduler;
  
  /**
   * <p>Creates {@link SocketAddress} instances, returning them through a {@link Promise}.</p>
   */
  public interface SocketAddressResolver
  {
      /**
       * 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
       */
      public void resolve(String host, int port, Promise<List<InetSocketAddress>> promise);
  
      /**
       * <p>Creates {@link SocketAddress} instances synchronously in the caller thread.</p>
       */
      @ManagedObject("The synchronous address resolver")
      public static class Sync implements SocketAddressResolver
      {
          @Override
          public void resolve(String host, int port, Promise<List<InetSocketAddress>> promise)
          {
              try
              {
                  InetAddress[] addresses = InetAddress.getAllByName(host);
  
                  List<InetSocketAddress> result = new ArrayList<>(addresses.length);
                  for (InetAddress address : addresses)
                      result.add(new InetSocketAddress(address, port));
  
                  if (result.isEmpty())
                      promise.failed(new UnknownHostException());
                  else
                      promise.succeeded(result);
              }
              catch (Throwable x)
              {
                  promise.failed(x);
              }
          }
      }
  
      /**
       * <p>Creates {@link SocketAddress} instances asynchronously in a different thread.</p>
       * <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>
       * <p>Example usage:</p>
       * <pre>
       * SocketAddressResolver resolver = new SocketAddressResolver.Async(executor, scheduler, timeout);
       * 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>
      */
     @ManagedObject("The asynchronous address resolver")
     public static class Async implements 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 Async(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;
         }
 
         @ManagedAttribute(value = "The timeout, in milliseconds, to resolve an address", readonly = true)
         public long getTimeout()
         {
             return timeout;
         }
 
         @Override
         public void resolve(final String host, final int port, final Promise<List<InetSocketAddress>> promise)
         {
             executor.execute(() ->
             {
                 Scheduler.Task task = null;
                 final AtomicBoolean complete = new AtomicBoolean();
                 if (timeout > 0)
                 {
                     final Thread thread = Thread.currentThread();
                     task = scheduler.schedule(() ->
                     {
                         if (complete.compareAndSet(false, true))
                         {
                             promise.failed(new TimeoutException("DNS timeout " + getTimeout() + " ms"));
                             thread.interrupt();
                         }
                     }, timeout, TimeUnit.MILLISECONDS);
                 }
 
                 try
                 {
                     long start = System.nanoTime();
                     InetAddress[] addresses = InetAddress.getAllByName(host);
                     long elapsed = System.nanoTime() - start;
                     if (LOG.isDebugEnabled())
                         LOG.debug("Resolved {} in {} ms", host, TimeUnit.NANOSECONDS.toMillis(elapsed));
 
                     List<InetSocketAddress> result = new ArrayList<>(addresses.length);
                     for (InetAddress address : addresses)
                         result.add(new InetSocketAddress(address, port));
 
                     if (complete.compareAndSet(false, true))
                     {
                         if (result.isEmpty())
                             promise.failed(new UnknownHostException());
                         else
                             promise.succeeded(result);
                     }
                 }
                 catch (Throwable x)
                 {
                     if (complete.compareAndSet(false, true))
                         promise.failed(x);
                 }
                 finally
                 {
                     if (task != null)
                         task.cancel();
                 }
             });
         }
     }
 }