/*
 * Copyright 2009 Red Hat, Inc.
 *
 * Red Hat 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 org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.Channels;
import org.jboss.netty.channel.MessageEvent;
import org.jboss.netty.channel.SimpleChannelHandler;
import org.jboss.netty.handler.codec.embedder.DecoderEmbedder;
import org.jboss.netty.handler.codec.embedder.EncoderEmbedder;
import org.jboss.netty.util.internal.LinkedTransferQueue;

/**
 *
 * @author The Netty Project (netty-dev@lists.jboss.org)
 * @author Trustin Lee (trustin@gmail.com)
 * @version $Rev$, $Date$
 */
public abstract class HttpContentEncoder extends SimpleChannelHandler {

    private final Queue<String> acceptEncodingQueue = new LinkedTransferQueue<String>();
    private volatile EncoderEmbedder<ChannelBuffer> encoder;

    /**
     * Creates a new instance.
     */
    protected HttpContentEncoder() {
        super();
    }

    @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;
        }
        acceptEncodingQueue.offer(acceptedEncoding);

        ctx.sendUpstream(e);
    }

    @Override
    public void writeRequested(ChannelHandlerContext ctx, MessageEvent e)
            throws Exception {

        Object msg = e.getMessage();
        if (msg instanceof HttpMessage) {
            HttpMessage m = (HttpMessage) msg;

            encoder = null;

            // Determine the content encoding.
            String acceptEncoding = acceptEncodingQueue.poll();
            if (acceptEncoding == null) {
                throw new IllegalStateException("cannot send more responses than requests");
            }

            if ((encoder = newContentEncoder(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()) {
                        // Note that HttpChunk is immutable unlike HttpMessage.
                        // XXX API inconsistency? I can live with it though.
                        Channels.write(
                                ctx, e.getFuture(), new DefaultHttpChunk(content), e.getRemoteAddress());
                    }
                } 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);
        }
    }

    /**
     * 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 DecoderEmbedder} if the specified encoding is supported.
     *         {@code null} otherwise (alternatively, you can throw an exception
     *         to block unknown encoding).
     */
    protected abstract EncoderEmbedder<ChannelBuffer> newContentEncoder(String acceptEncoding) throws Exception;

    /**
     * Returns the expected content encoding of the encoded content.
     *
     * @param contentEncoding the content encoding of the original content
     * @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() {
        ChannelBuffer result;
        if (encoder.finish()) {
            result = ChannelBuffers.wrappedBuffer(encoder.pollAll(new ChannelBuffer[encoder.size()]));
        } else {
            result = ChannelBuffers.EMPTY_BUFFER;
        }
        encoder = null;
        return result;
    }
}