//
   //  ========================================================================
   //  Copyright (c) 1995-2015 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;
  
  import java.io.Closeable;
  import java.nio.ByteBuffer;
  import java.util.Collections;
  import java.util.Iterator;
  
  import org.eclipse.jetty.client.api.ContentProvider;
  import org.eclipse.jetty.util.BufferUtil;
  import org.eclipse.jetty.util.Callback;
  import org.eclipse.jetty.util.log.Log;
  import org.eclipse.jetty.util.log.Logger;
  
  /**
   * {@link HttpContent} is a stateful, linear representation of the request content provided
   * by a {@link ContentProvider} that can be traversed one-way to obtain content buffers to
   * send to a HTTP server.
   * <p />
   * {@link HttpContent} offers the notion of a one-way cursor to traverse the content.
   * The cursor starts in a virtual "before" position and can be advanced using {@link #advance()}
   * until it reaches a virtual "after" position where the content is fully consumed.
   * <pre>
   *      +---+  +---+  +---+  +---+  +---+
   *      |   |  |   |  |   |  |   |  |   |
   *      +---+  +---+  +---+  +---+  +---+
   *   ^           ^                    ^    ^
   *   |           | --> advance()      |    |
   *   |           |                  last   |
   *   |           |                         |
   * before        |                        after
   *               |
   *            current
   * </pre>
   * At each valid (non-before and non-after) cursor position, {@link HttpContent} provides the following state:
   * <ul>
   * <li>the buffer containing the content to send, via {@link #getByteBuffer()}</li>
   * <li>a copy of the content buffer that can be used for notifications, via {@link #getContent()}</li>
   * <li>whether the buffer to write is the last one, via {@link #isLast()}</li>
   * </ul>
   * {@link HttpContent} may not have content, if the related {@link ContentProvider} is {@code null}, and this
   * is reflected by {@link #hasContent()}.
   * <p />
   * {@link HttpContent} may have {@link AsyncContentProvider deferred content}, in which case {@link #advance()}
   * moves the cursor to a position that provides {@code null} {@link #getByteBuffer() buffer} and
   * {@link #getContent() content}. When the deferred content is available, a further call to {@link #advance()}
   * will move the cursor to a position that provides non {@code null} buffer and content.
   */
  public class HttpContent implements Callback, Closeable
  {
      private static final Logger LOG = Log.getLogger(HttpContent.class);
      private static final ByteBuffer AFTER = ByteBuffer.allocate(0);
  
      private final ContentProvider provider;
      private final Iterator<ByteBuffer> iterator;
      private ByteBuffer buffer;
      private volatile ByteBuffer content;
  
      public HttpContent(ContentProvider provider)
      {
          this.provider = provider;
          this.iterator = provider == null ? Collections.<ByteBuffer>emptyIterator() : provider.iterator();
      }
  
      /**
       * @return whether there is any content at all
       */
      public boolean hasContent()
      {
          return provider != null;
      }
  
      /**
       * @return whether the cursor points to the last content
       */
      public boolean isLast()
      {
          return !iterator.hasNext();
      }
  
      /**
       * @return the {@link ByteBuffer} containing the content at the cursor's position
      */
     public ByteBuffer getByteBuffer()
     {
         return buffer;
     }
 
     /**
      * @return a {@link ByteBuffer#slice()} of {@link #getByteBuffer()} at the cursor's position
      */
     public ByteBuffer getContent()
     {
         return content;
     }
 
     /**
      * Advances the cursor to the next block of content.
      * <p />
      * The next block of content may be valid (which yields a non-null buffer
      * returned by {@link #getByteBuffer()}), but may also be deferred
      * (which yields a null buffer returned by {@link #getByteBuffer()}).
      * <p />
      * If the block of content pointed by the new cursor position is valid, this method returns true.
      *
      * @return true if there is content at the new cursor's position, false otherwise.
      */
     public boolean advance()
     {
         boolean advanced;
         boolean hasNext;
         ByteBuffer bytes;
         if (iterator instanceof Synchronizable)
         {
             synchronized (((Synchronizable)iterator).getLock())
             {
                 advanced = iterator.hasNext();
                 bytes = advanced ? iterator.next() : null;
                 hasNext = advanced && iterator.hasNext();
             }
         }
         else
         {
             advanced = iterator.hasNext();
             bytes = advanced ? iterator.next() : null;
             hasNext = advanced && iterator.hasNext();
         }
 
         if (advanced)
         {
             buffer = bytes;
             content = bytes == null ? null : bytes.slice();
             if (LOG.isDebugEnabled())
                 LOG.debug("Advanced content to {} chunk {}", hasNext ? "next" : "last", bytes);
             return bytes != null;
         }
         else
         {
             if (content != AFTER)
             {
                 content = buffer = AFTER;
                 if (LOG.isDebugEnabled())
                     LOG.debug("Advanced content past last chunk");
             }
             return false;
         }
     }
 
     /**
      * @return whether the cursor has been advanced past the {@link #isLast() last} position.
      */
     public boolean isConsumed()
     {
         return content == AFTER;
     }
 
     @Override
     public void succeeded()
     {
         if (isConsumed())
             return;
         if (iterator instanceof Callback)
             ((Callback)iterator).succeeded();
     }
 
     @Override
     public void failed(Throwable x)
     {
         if (isConsumed())
             return;
         if (iterator instanceof Callback)
             ((Callback)iterator).failed(x);
     }
 
     @Override
     public void close()
     {
         try
         {
             if (iterator instanceof Closeable)
                 ((Closeable)iterator).close();
         }
         catch (Exception x)
         {
             LOG.ignore(x);
         }
     }
 
     @Override
     public String toString()
     {
         return String.format("%s@%x - has=%b,last=%b,consumed=%b,buffer=%s",
                 getClass().getSimpleName(),
                 hashCode(),
                 hasContent(),
                 isLast(),
                 isConsumed(),
                 BufferUtil.toDetailString(getContent()));
     }
 }