//
   //  ========================================================================
   //  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.client.util;
  
  import java.io.Closeable;
  import java.nio.ByteBuffer;
  import java.util.Iterator;
  import java.util.NoSuchElementException;
  import java.util.Queue;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.eclipse.jetty.client.AsyncContentProvider;
  import org.eclipse.jetty.client.api.ContentProvider;
  import org.eclipse.jetty.client.api.Request;
  import org.eclipse.jetty.client.api.Response;
  
  /**
   * A {@link ContentProvider} that allows to add content after {@link Request#send(Response.CompleteListener)}
   * has been called, therefore providing the request content at a later time.
   * <p />
   * {@link DeferredContentProvider} can only be used in conjunction with
   * {@link Request#send(Response.CompleteListener)} (and not with its blocking counterpart {@link Request#send()})
   * because it provides content asynchronously.
   * <p />
   * The deferred content is provided once and then fully consumed.
   * Invocations to the {@link #iterator()} method after the first will return an "empty" iterator
   * because the stream has been consumed on the first invocation.
   * However, it is possible for subclasses to override {@link #offer(ByteBuffer)} and {@link #close()} to copy
   * the content to another location (for example a file) and be able to support multiple invocations
   * of of {@link #iterator()} returning the iterator provided by this
    * class on the first invocation, and an iterator on the bytes copied to the other location
    * for subsequent invocations.
   * <p />
   * Typical usage of {@link DeferredContentProvider} is in asynchronous proxies, where HTTP headers arrive
   * separately from HTTP content chunks.
   * <p />
   * The deferred content must be provided through {@link #offer(ByteBuffer)}, which can be invoked multiple
   * times, and when all content has been provided it must be signaled with a call to {@link #close()}.
   * <p />
   * Example usage:
   * <pre>
   * HttpClient httpClient = ...;
   *
   * // Use try-with-resources to autoclose DeferredContentProvider
   * try (DeferredContentProvider content = new DeferredContentProvider())
   * {
   *     httpClient.newRequest("localhost", 8080)
   *             .content(content)
   *             .send(new Response.CompleteListener()
   *             {
   *                 &#64Override
   *                 public void onComplete(Result result)
   *                 {
   *                     // Your logic here
   *                 }
   *             });
   *
   *     // At a later time...
   *     content.offer(ByteBuffer.wrap("some content".getBytes()));
   * }
   * </pre>
   */
  public class DeferredContentProvider implements AsyncContentProvider, Closeable
  {
      private static final ByteBuffer CLOSE = ByteBuffer.allocate(0);
  
      private final Queue<ByteBuffer> chunks = new ConcurrentLinkedQueue<>();
      private final AtomicReference<Listener> listener = new AtomicReference<>();
      private final Iterator<ByteBuffer> iterator = new DeferredContentProviderIterator();
      private final AtomicBoolean closed = new AtomicBoolean();
  
      /**
       * Creates a new {@link DeferredContentProvider} with the given initial content
       *
       * @param buffers the initial content
       */
      public DeferredContentProvider(ByteBuffer... buffers)
      {
          for (ByteBuffer buffer : buffers)
              chunks.offer(buffer);
      }
 
     @Override
     public void setListener(Listener listener)
     {
         if (!this.listener.compareAndSet(null, listener))
             throw new IllegalStateException();
     }
 
     @Override
     public long getLength()
     {
         return -1;
     }
 
     /**
      * Adds the given content buffer to this content provider
      * and notifies the listener that content is available.
      *
      * @param buffer the content to add
      * @return true if the content was added, false otherwise
      */
     public boolean offer(ByteBuffer buffer)
     {
         boolean result = chunks.offer(buffer);
         notifyListener();
         return result;
     }
 
     /**
      * No more content will be added to this content provider
      * and notifies the listener that no more content is available.
      */
     public void close()
     {
         if (closed.compareAndSet(false, true))
         {
             chunks.offer(CLOSE);
             notifyListener();
         }
     }
 
     private void notifyListener()
     {
         Listener listener = this.listener.get();
         if (listener != null)
             listener.onContent();
     }
 
     @Override
     public Iterator<ByteBuffer> iterator()
     {
         return iterator;
     }
 
     private class DeferredContentProviderIterator implements Iterator<ByteBuffer>
     {
         @Override
         public boolean hasNext()
         {
             return chunks.peek() != CLOSE;
         }
 
         @Override
         public ByteBuffer next()
         {
             ByteBuffer element = chunks.poll();
             if (element == CLOSE)
                 throw new NoSuchElementException();
             return element;
         }
 
         @Override
         public void remove()
         {
             throw new UnsupportedOperationException();
         }
     }
 }