//
   //  ========================================================================
   //  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.client.util;
  
  import java.io.Closeable;
  import java.io.IOException;
  import java.io.InterruptedIOException;
  import java.nio.ByteBuffer;
  import java.util.ArrayDeque;
  import java.util.ArrayList;
  import java.util.Deque;
  import java.util.Iterator;
  import java.util.List;
  import java.util.NoSuchElementException;
  import java.util.Objects;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.eclipse.jetty.client.AsyncContentProvider;
  import org.eclipse.jetty.client.Synchronizable;
  import org.eclipse.jetty.client.api.ContentProvider;
  import org.eclipse.jetty.client.api.Request;
  import org.eclipse.jetty.client.api.Response;
  import org.eclipse.jetty.util.BufferUtil;
  import org.eclipse.jetty.util.Callback;
  
  /**
   * 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()
   *             {
   *                 &#64;Override
   *                 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, Callback, Closeable
  {
      private static final Chunk CLOSE = new Chunk(BufferUtil.EMPTY_BUFFER, Callback.NOOP);
  
      private final Object lock = this;
      private final Deque<Chunk> chunks = new ArrayDeque<>();
      private final AtomicReference<Listener> listener = new AtomicReference<>();
      private final DeferredContentProviderIterator iterator = new DeferredContentProviderIterator();
      private final AtomicBoolean closed = new AtomicBoolean();
      private long length = -1;
      private int size;
     private Throwable failure;
 
     /**
      * Creates a new {@link DeferredContentProvider} with the given initial content
      *
      * @param buffers the initial content
      */
     public DeferredContentProvider(ByteBuffer... buffers)
     {
         for (ByteBuffer buffer : buffers)
             offer(buffer);
     }
 
     @Override
     public void setListener(Listener listener)
     {
         if (!this.listener.compareAndSet(null, listener))
             throw new IllegalStateException(String.format("The same %s instance cannot be used in multiple requests",
                     AsyncContentProvider.class.getName()));
 
         if (isClosed())
         {
             synchronized (lock)
             {
                 long total = 0;
                 for (Chunk chunk : chunks)
                     total += chunk.buffer.remaining();
                 length = total;
             }
         }
     }
 
     @Override
     public long getLength()
     {
         return length;
     }
 
     /**
      * 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)
     {
         return offer(buffer, Callback.NOOP);
     }
 
     public boolean offer(ByteBuffer buffer, Callback callback)
     {
         return offer(new Chunk(buffer, callback));
     }
 
     private boolean offer(Chunk chunk)
     {
         Throwable failure;
         boolean result = false;
         synchronized (lock)
         {
             failure = this.failure;
             if (failure == null)
             {
                 result = chunks.offer(chunk);
                 if (result && chunk != CLOSE)
                     ++size;
             }
         }
         if (failure != null)
             chunk.callback.failed(failure);
         else if (result)
             notifyListener();
         return result;
     }
 
     private void clear()
     {
         synchronized (lock)
         {
             chunks.clear();
         }
     }
 
     public void flush() throws IOException
     {
         synchronized (lock)
         {
             try
             {
                 while (true)
                 {
                     if (failure != null)
                         throw new IOException(failure);
                     if (size == 0)
                         break;
                     lock.wait();
                 }
             }
             catch (InterruptedException x)
             {
                 throw new InterruptedIOException();
             }
         }
     }
 
     /**
      * 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))
             offer(CLOSE);
     }
 
     public boolean isClosed()
     {
         return closed.get();
     }
 
     @Override
     public void failed(Throwable failure)
     {
         iterator.failed(failure);
     }
 
     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>, Callback, Synchronizable
     {
         private Chunk current;
 
         @Override
         public boolean hasNext()
         {
             synchronized (lock)
             {
                 return chunks.peek() != CLOSE;
             }
         }
 
         @Override
         public ByteBuffer next()
         {
             synchronized (lock)
             {
                 Chunk chunk = current = chunks.poll();
                 if (chunk == CLOSE)
                 {
                     // Slow path: reinsert the CLOSE chunk
                     // so that hasNext() works correctly.
                     chunks.offerFirst(CLOSE);
                     throw new NoSuchElementException();
                 }
                 return chunk == null ? null : chunk.buffer;
             }
         }
 
         @Override
         public void remove()
         {
             throw new UnsupportedOperationException();
         }
 
         @Override
         public void succeeded()
         {
             Chunk chunk;
             synchronized (lock)
             {
                 chunk = current;
                 if (chunk != null)
                 {
                     --size;
                     lock.notify();
                 }
             }
             if (chunk != null)
                 chunk.callback.succeeded();
         }
 
         @Override
         public void failed(Throwable x)
         {
             List<Chunk> chunks = new ArrayList<>();
             synchronized (lock)
             {
                 failure = x;
                 // Transfer all chunks to fail them all.
                 Chunk chunk = current;
                 current = null;
                 if (chunk != null)
                     chunks.add(chunk);
                 chunks.addAll(DeferredContentProvider.this.chunks);
                 clear();
                 lock.notify();
             }
             for (Chunk chunk : chunks)
                 chunk.callback.failed(x);
         }
 
         @Override
         public Object getLock()
         {
             return lock;
         }
     }
 
     public static class Chunk
     {
         public final ByteBuffer buffer;
         public final Callback callback;
 
         public Chunk(ByteBuffer buffer, Callback callback)
         {
             this.buffer = Objects.requireNonNull(buffer);
             this.callback = Objects.requireNonNull(callback);
         }
 
         @Override
         public String toString()
         {
             return String.format("%s@%x", getClass().getSimpleName(), hashCode());
         }
     }
 }