/*
    * Copyright 2012 The Netty Project
    *
    * The Netty Project licenses this file to you under the Apache License,
    * version 2.0 (the "License"); you may not use this file except in compliance
    * with the License. You may obtain a copy of the License at:
    *
    *   http://www.apache.org/licenses/LICENSE-2.0
    *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
   * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
   * License for the specific language governing permissions and limitations
   * under the License.
   */
  package org.jboss.netty.handler.codec.http;
  
  import java.util.Queue;
  import java.util.concurrent.ConcurrentLinkedQueue;
  
  import org.jboss.netty.buffer.ChannelBuffer;
  import org.jboss.netty.buffer.ChannelBuffers;
  import org.jboss.netty.channel.ChannelHandlerContext;
  import org.jboss.netty.channel.ChannelStateEvent;
  import org.jboss.netty.channel.Channels;
  import org.jboss.netty.channel.LifeCycleAwareChannelHandler;
  import org.jboss.netty.channel.MessageEvent;
  import org.jboss.netty.channel.SimpleChannelHandler;
  import org.jboss.netty.handler.codec.embedder.EncoderEmbedder;
  
  /**
   * Encodes the content of the outbound {@link HttpResponse} and {@link HttpChunk}.
   * The original content is replaced with the new content encoded by the
   * {@link EncoderEmbedder}, which is created by {@link #newContentEncoder(HttpMessage, String)}.
   * Once encoding is finished, the value of the <tt>'Content-Encoding'</tt> header
   * is set to the target content encoding, as returned by {@link #getTargetContentEncoding(String)}.
   * Also, the <tt>'Content-Length'</tt> header is updated to the length of the
   * encoded content.  If there is no supported encoding in the
   * corresponding {@link HttpRequest}'s {@code "Accept-Encoding"} header,
   * {@link #newContentEncoder(HttpMessage, String)} should return {@code null} so that no
   * encoding occurs (i.e. pass-through).
   * <p>
   * Please note that this is an abstract class.  You have to extend this class
   * and implement {@link #newContentEncoder(HttpMessage, String)} and {@link #getTargetContentEncoding(String)}
   * properly to make this class functional.  For example, refer to the source
   * code of {@link HttpContentCompressor}.
   * <p>
   * This handler must be placed after {@link HttpMessageEncoder} in the pipeline
   * so that this handler can intercept HTTP responses before {@link HttpMessageEncoder}
   * converts them into {@link ChannelBuffer}s.
   */
  public abstract class HttpContentEncoder extends SimpleChannelHandler
                                           implements LifeCycleAwareChannelHandler {
  
      private final Queue<String> acceptEncodingQueue = new ConcurrentLinkedQueue<String>();
      private volatile EncoderEmbedder<ChannelBuffer> encoder;
  
      /**
       * Creates a new instance.
       */
      protected HttpContentEncoder() {
      }
  
      @Override
      public void messageReceived(ChannelHandlerContext ctx, MessageEvent e)
              throws Exception {
          Object msg = e.getMessage();
          if (!(msg instanceof HttpMessage)) {
              ctx.sendUpstream(e);
              return;
          }
  
          HttpMessage m = (HttpMessage) msg;
          String acceptedEncoding = m.getHeader(HttpHeaders.Names.ACCEPT_ENCODING);
          if (acceptedEncoding == null) {
              acceptedEncoding = HttpHeaders.Values.IDENTITY;
          }
          boolean offered = acceptEncodingQueue.offer(acceptedEncoding);
          assert offered;
  
          ctx.sendUpstream(e);
      }
  
      @Override
      public void writeRequested(ChannelHandlerContext ctx, MessageEvent e)
              throws Exception {
  
          Object msg = e.getMessage();
          if (msg instanceof HttpResponse && ((HttpResponse) msg).getStatus().getCode() == 100) {
              // 100-continue response must be passed through.
              ctx.sendDownstream(e);
          } else  if (msg instanceof HttpMessage) {
              HttpMessage m = (HttpMessage) msg;
  
              // Clean-up the previous encoder if not cleaned up correctly.
              finishEncode();
  
              String acceptEncoding = acceptEncodingQueue.poll();
              if (acceptEncoding == null) {
                 throw new IllegalStateException("cannot send more responses than requests");
             }
 
             String contentEncoding = m.getHeader(HttpHeaders.Names.CONTENT_ENCODING);
             if (contentEncoding != null &&
                 !HttpHeaders.Values.IDENTITY.equalsIgnoreCase(contentEncoding)) {
                 // Content-Encoding is set already and it is not 'identity'.
                 ctx.sendDownstream(e);
             } else {
                 // Determine the content encoding.
                 boolean hasContent = m.isChunked() || m.getContent().readable();
                 if (hasContent && (encoder = newContentEncoder(m, acceptEncoding)) != null) {
                     // Encode the content and remove or replace the existing headers
                     // so that the message looks like a decoded message.
                     m.setHeader(
                             HttpHeaders.Names.CONTENT_ENCODING,
                             getTargetContentEncoding(acceptEncoding));
 
                     if (!m.isChunked()) {
                         ChannelBuffer content = m.getContent();
                         // Encode the content.
                         content = ChannelBuffers.wrappedBuffer(
                                 encode(content), finishEncode());
 
                         // Replace the content.
                         m.setContent(content);
                         if (m.containsHeader(HttpHeaders.Names.CONTENT_LENGTH)) {
                             m.setHeader(
                                     HttpHeaders.Names.CONTENT_LENGTH,
                                     Integer.toString(content.readableBytes()));
                         }
                     }
                 }
 
                 // Because HttpMessage is a mutable object, we can simply forward the write request.
                 ctx.sendDownstream(e);
             }
         } else if (msg instanceof HttpChunk) {
             HttpChunk c = (HttpChunk) msg;
             ChannelBuffer content = c.getContent();
 
             // Encode the chunk if necessary.
             if (encoder != null) {
                 if (!c.isLast()) {
                     content = encode(content);
                     if (content.readable()) {
                         c.setContent(content);
                         ctx.sendDownstream(e);
                     }
                 } else {
                     ChannelBuffer lastProduct = finishEncode();
 
                     // Generate an additional chunk if the decoder produced
                     // the last product on closure,
                     if (lastProduct.readable()) {
                         Channels.write(
                                 ctx, Channels.succeededFuture(e.getChannel()),
                                 new DefaultHttpChunk(lastProduct), e.getRemoteAddress());
                     }
 
                     // Emit the last chunk.
                     ctx.sendDownstream(e);
                 }
             } else {
                 ctx.sendDownstream(e);
             }
         } else {
             ctx.sendDownstream(e);
         }
     }
 
     @Override
     public void channelClosed(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
         // Clean-up the previous encoder if not cleaned up correctly.
         finishEncode();
 
         super.channelClosed(ctx, e);
     }
 
     /**
      * Returns a new {@link EncoderEmbedder} that encodes the HTTP message
      * content.
      *
      * @param acceptEncoding
      *        the value of the {@code "Accept-Encoding"} header
      *
      * @return a new {@link EncoderEmbedder} if there is a supported encoding
      *         in {@code acceptEncoding}.  {@code null} otherwise.
      */
     protected abstract EncoderEmbedder<ChannelBuffer> newContentEncoder(
             HttpMessage msg, String acceptEncoding) throws Exception;
 
     /**
      * Returns the expected content encoding of the encoded content.
      *
      * @param acceptEncoding the value of the {@code "Accept-Encoding"} header
      * @return the expected content encoding of the new content
      */
     protected abstract String getTargetContentEncoding(String acceptEncoding) throws Exception;
 
     private ChannelBuffer encode(ChannelBuffer buf) {
         encoder.offer(buf);
         return ChannelBuffers.wrappedBuffer(encoder.pollAll(new ChannelBuffer[encoder.size()]));
     }
 
     private ChannelBuffer finishEncode() {
         if (encoder == null) {
             return ChannelBuffers.EMPTY_BUFFER;
         }
 
         ChannelBuffer result;
         if (encoder.finish()) {
             result = ChannelBuffers.wrappedBuffer(encoder.pollAll(new ChannelBuffer[encoder.size()]));
         } else {
             result = ChannelBuffers.EMPTY_BUFFER;
         }
         encoder = null;
         return result;
     }
 
     public void beforeAdd(ChannelHandlerContext ctx) throws Exception {
         // NOOP
     }
 
     public void afterAdd(ChannelHandlerContext ctx) throws Exception {
         // NOOP
     }
 
     public void beforeRemove(ChannelHandlerContext ctx) throws Exception {
         // NOOP
     }
 
     public void afterRemove(ChannelHandlerContext ctx) throws Exception {
         finishEncode();
     }
 }