/*
 * 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 io.netty.handler.codec.spdy;

import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToMessageEncoder;
import io.netty.handler.codec.UnsupportedMessageTypeException;
import io.netty.handler.codec.http.FullHttpMessage;
import io.netty.handler.codec.http.HttpContent;
import io.netty.handler.codec.http.HttpHeaderNames;
import io.netty.handler.codec.http.HttpHeaders;
import io.netty.handler.codec.http.HttpMessage;
import io.netty.handler.codec.http.HttpObject;
import io.netty.handler.codec.http.HttpRequest;
import io.netty.handler.codec.http.HttpResponse;
import io.netty.handler.codec.http.LastHttpContent;
import io.netty.util.AsciiString;

import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;

Encodes HttpRequests, HttpResponses, and HttpContents into SpdySynStreamFrames and SpdySynReplyFrames. 
Request Annotations
 SPDY specific headers must be added to HttpRequests: 


Header Name
Header Value


"X-SPDY-Stream-ID"
The Stream-ID for this request.
Stream-IDs must be odd, positive integers, and must increase monotonically.


"X-SPDY-Priority"
The priority value for this request.
The priority should be between 0 and 7 inclusive.
0 represents the highest priority and 7 represents the lowest.
This header is optional and defaults to 0.


Response Annotations
 SPDY specific headers must be added to HttpResponses: 


Header Name
Header Value


"X-SPDY-Stream-ID"
The Stream-ID of the request corresponding to this response.


Pushed Resource Annotations
 SPDY specific headers must be added to pushed HttpRequests: 


Header Name
Header Value


"X-SPDY-Stream-ID"
The Stream-ID for this resource.
Stream-IDs must be even, positive integers, and must increase monotonically.


"X-SPDY-Associated-To-Stream-ID"
The Stream-ID of the request that initiated this pushed resource.


"X-SPDY-Priority"
The priority value for this resource.
The priority should be between 0 and 7 inclusive.
0 represents the highest priority and 7 represents the lowest.
This header is optional and defaults to 0.


Required Annotations
SPDY requires that all Requests and Pushed Resources contain
an HTTP "Host" header.
Optional Annotations
 Requests and Pushed Resources must contain a SPDY scheme header. This can be set via the "X-SPDY-Scheme" header but otherwise defaults to "https" as that is the most common SPDY deployment. 
Chunked Content
 This encoder associates all HttpContents that it receives with the most recently received 'chunked' HttpRequest or HttpResponse. 
Pushed Resources
All pushed resources should be sent before sending the response
that corresponds to the initial request.
/**
 * Encodes {@link HttpRequest}s, {@link HttpResponse}s, and {@link HttpContent}s
 * into {@link SpdySynStreamFrame}s and {@link SpdySynReplyFrame}s.
 *
 * <h3>Request Annotations</h3>
 *
 * SPDY specific headers must be added to {@link HttpRequest}s:
 * <table border=1>
 * <tr>
 * <th>Header Name</th><th>Header Value</th>
 * </tr>
 * <tr>
 * <td>{@code "X-SPDY-Stream-ID"}</td>
 * <td>The Stream-ID for this request.
 * Stream-IDs must be odd, positive integers, and must increase monotonically.</td>
 * </tr>
 * <tr>
 * <td>{@code "X-SPDY-Priority"}</td>
 * <td>The priority value for this request.
 * The priority should be between 0 and 7 inclusive.
 * 0 represents the highest priority and 7 represents the lowest.
 * This header is optional and defaults to 0.</td>
 * </tr>
 * </table>
 *
 * <h3>Response Annotations</h3>
 *
 * SPDY specific headers must be added to {@link HttpResponse}s:
 * <table border=1>
 * <tr>
 * <th>Header Name</th><th>Header Value</th>
 * </tr>
 * <tr>
 * <td>{@code "X-SPDY-Stream-ID"}</td>
 * <td>The Stream-ID of the request corresponding to this response.</td>
 * </tr>
 * </table>
 *
 * <h3>Pushed Resource Annotations</h3>
 *
 * SPDY specific headers must be added to pushed {@link HttpRequest}s:
 * <table border=1>
 * <tr>
 * <th>Header Name</th><th>Header Value</th>
 * </tr>
 * <tr>
 * <td>{@code "X-SPDY-Stream-ID"}</td>
 * <td>The Stream-ID for this resource.
 * Stream-IDs must be even, positive integers, and must increase monotonically.</td>
 * </tr>
 * <tr>
 * <td>{@code "X-SPDY-Associated-To-Stream-ID"}</td>
 * <td>The Stream-ID of the request that initiated this pushed resource.</td>
 * </tr>
 * <tr>
 * <td>{@code "X-SPDY-Priority"}</td>
 * <td>The priority value for this resource.
 * The priority should be between 0 and 7 inclusive.
 * 0 represents the highest priority and 7 represents the lowest.
 * This header is optional and defaults to 0.</td>
 * </tr>
 * </table>
 *
 * <h3>Required Annotations</h3>
 *
 * SPDY requires that all Requests and Pushed Resources contain
 * an HTTP "Host" header.
 *
 * <h3>Optional Annotations</h3>
 *
 * Requests and Pushed Resources must contain a SPDY scheme header.
 * This can be set via the {@code "X-SPDY-Scheme"} header but otherwise
 * defaults to "https" as that is the most common SPDY deployment.
 *
 * <h3>Chunked Content</h3>
 *
 * This encoder associates all {@link HttpContent}s that it receives
 * with the most recently received 'chunked' {@link HttpRequest}
 * or {@link HttpResponse}.
 *
 * <h3>Pushed Resources</h3>
 *
 * All pushed resources should be sent before sending the response
 * that corresponds to the initial request.
 */
public class SpdyHttpEncoder extends MessageToMessageEncoder<HttpObject> {

    private int currentStreamId;

    private final boolean validateHeaders;
    private final boolean headersToLowerCase;

    
Creates a new instance.
Params:
version – the protocol version/**
     * Creates a new instance.
     *
     * @param version the protocol version
     */
    public SpdyHttpEncoder(SpdyVersion version) {
        this(version, true, true);
    }

    
Creates a new instance.
Params:
version –            the protocol version
headersToLowerCase – convert header names to lowercase. In a controlled environment,
                          one can disable the conversion.
validateHeaders –  validate the header names and values when adding them to the SpdyHeaders/**
     * Creates a new instance.
     *
     * @param version            the protocol version
     * @param headersToLowerCase convert header names to lowercase. In a controlled environment,
     *                           one can disable the conversion.
     * @param validateHeaders    validate the header names and values when adding them to the {@link SpdyHeaders}
     */
    public SpdyHttpEncoder(SpdyVersion version, boolean headersToLowerCase, boolean validateHeaders) {
        if (version == null) {
            throw new NullPointerException("version");
        }
        this.headersToLowerCase = headersToLowerCase;
        this.validateHeaders = validateHeaders;
    }

    @Override
    protected void encode(ChannelHandlerContext ctx, HttpObject msg, List<Object> out) throws Exception {

        boolean valid = false;
        boolean last = false;

        if (msg instanceof HttpRequest) {

            HttpRequest httpRequest = (HttpRequest) msg;
            SpdySynStreamFrame spdySynStreamFrame = createSynStreamFrame(httpRequest);
            out.add(spdySynStreamFrame);

            last = spdySynStreamFrame.isLast() || spdySynStreamFrame.isUnidirectional();
            valid = true;
        }
        if (msg instanceof HttpResponse) {

            HttpResponse httpResponse = (HttpResponse) msg;
            SpdyHeadersFrame spdyHeadersFrame = createHeadersFrame(httpResponse);
            out.add(spdyHeadersFrame);

            last = spdyHeadersFrame.isLast();
            valid = true;
        }
        if (msg instanceof HttpContent && !last) {

            HttpContent chunk = (HttpContent) msg;

            chunk.content().retain();
            SpdyDataFrame spdyDataFrame = new DefaultSpdyDataFrame(currentStreamId, chunk.content());
            if (chunk instanceof LastHttpContent) {
                LastHttpContent trailer = (LastHttpContent) chunk;
                HttpHeaders trailers = trailer.trailingHeaders();
                if (trailers.isEmpty()) {
                    spdyDataFrame.setLast(true);
                    out.add(spdyDataFrame);
                } else {
                    // Create SPDY HEADERS frame out of trailers
                    SpdyHeadersFrame spdyHeadersFrame = new DefaultSpdyHeadersFrame(currentStreamId, validateHeaders);
                    spdyHeadersFrame.setLast(true);
                    Iterator<Entry<CharSequence, CharSequence>> itr = trailers.iteratorCharSequence();
                    while (itr.hasNext()) {
                        Map.Entry<CharSequence, CharSequence> entry = itr.next();
                        final CharSequence headerName =
                                headersToLowerCase ? AsciiString.of(entry.getKey()).toLowerCase() : entry.getKey();
                        spdyHeadersFrame.headers().add(headerName, entry.getValue());
                    }

                    // Write DATA frame and append HEADERS frame
                    out.add(spdyDataFrame);
                    out.add(spdyHeadersFrame);
                }
            } else {
                out.add(spdyDataFrame);
            }

            valid = true;
        }

        if (!valid) {
            throw new UnsupportedMessageTypeException(msg);
        }
    }

    @SuppressWarnings("deprecation")
    private SpdySynStreamFrame createSynStreamFrame(HttpRequest httpRequest) throws Exception {
        // Get the Stream-ID, Associated-To-Stream-ID, Priority, and scheme from the headers
        final HttpHeaders httpHeaders = httpRequest.headers();
        int streamId = httpHeaders.getInt(SpdyHttpHeaders.Names.STREAM_ID);
        int associatedToStreamId = httpHeaders.getInt(SpdyHttpHeaders.Names.ASSOCIATED_TO_STREAM_ID, 0);
        byte priority = (byte) httpHeaders.getInt(SpdyHttpHeaders.Names.PRIORITY, 0);
        CharSequence scheme = httpHeaders.get(SpdyHttpHeaders.Names.SCHEME);
        httpHeaders.remove(SpdyHttpHeaders.Names.STREAM_ID);
        httpHeaders.remove(SpdyHttpHeaders.Names.ASSOCIATED_TO_STREAM_ID);
        httpHeaders.remove(SpdyHttpHeaders.Names.PRIORITY);
        httpHeaders.remove(SpdyHttpHeaders.Names.SCHEME);

        // The Connection, Keep-Alive, Proxy-Connection, and Transfer-Encoding
        // headers are not valid and MUST not be sent.
        httpHeaders.remove(HttpHeaderNames.CONNECTION);
        httpHeaders.remove("Keep-Alive");
        httpHeaders.remove("Proxy-Connection");
        httpHeaders.remove(HttpHeaderNames.TRANSFER_ENCODING);

        SpdySynStreamFrame spdySynStreamFrame =
                new DefaultSpdySynStreamFrame(streamId, associatedToStreamId, priority, validateHeaders);

        // Unfold the first line of the message into name/value pairs
        SpdyHeaders frameHeaders = spdySynStreamFrame.headers();
        frameHeaders.set(SpdyHeaders.HttpNames.METHOD, httpRequest.method().name());
        frameHeaders.set(SpdyHeaders.HttpNames.PATH, httpRequest.uri());
        frameHeaders.set(SpdyHeaders.HttpNames.VERSION, httpRequest.protocolVersion().text());

        // Replace the HTTP host header with the SPDY host header
        CharSequence host = httpHeaders.get(HttpHeaderNames.HOST);
        httpHeaders.remove(HttpHeaderNames.HOST);
        frameHeaders.set(SpdyHeaders.HttpNames.HOST, host);

        // Set the SPDY scheme header
        if (scheme == null) {
            scheme = "https";
        }
        frameHeaders.set(SpdyHeaders.HttpNames.SCHEME, scheme);

        // Transfer the remaining HTTP headers
        Iterator<Entry<CharSequence, CharSequence>> itr = httpHeaders.iteratorCharSequence();
        while (itr.hasNext()) {
            Map.Entry<CharSequence, CharSequence> entry = itr.next();
            final CharSequence headerName =
                    headersToLowerCase ? AsciiString.of(entry.getKey()).toLowerCase() : entry.getKey();
            frameHeaders.add(headerName, entry.getValue());
        }
        currentStreamId = spdySynStreamFrame.streamId();
        if (associatedToStreamId == 0) {
            spdySynStreamFrame.setLast(isLast(httpRequest));
        } else {
            spdySynStreamFrame.setUnidirectional(true);
        }

        return spdySynStreamFrame;
    }

    @SuppressWarnings("deprecation")
    private SpdyHeadersFrame createHeadersFrame(HttpResponse httpResponse) throws Exception {
        // Get the Stream-ID from the headers
        final HttpHeaders httpHeaders = httpResponse.headers();
        int streamId = httpHeaders.getInt(SpdyHttpHeaders.Names.STREAM_ID);
        httpHeaders.remove(SpdyHttpHeaders.Names.STREAM_ID);

        // The Connection, Keep-Alive, Proxy-Connection, and Transfer-Encoding
        // headers are not valid and MUST not be sent.
        httpHeaders.remove(HttpHeaderNames.CONNECTION);
        httpHeaders.remove("Keep-Alive");
        httpHeaders.remove("Proxy-Connection");
        httpHeaders.remove(HttpHeaderNames.TRANSFER_ENCODING);

        SpdyHeadersFrame spdyHeadersFrame;
        if (SpdyCodecUtil.isServerId(streamId)) {
            spdyHeadersFrame = new DefaultSpdyHeadersFrame(streamId, validateHeaders);
        } else {
            spdyHeadersFrame = new DefaultSpdySynReplyFrame(streamId, validateHeaders);
        }
        SpdyHeaders frameHeaders = spdyHeadersFrame.headers();
        // Unfold the first line of the response into name/value pairs
        frameHeaders.set(SpdyHeaders.HttpNames.STATUS, httpResponse.status().codeAsText());
        frameHeaders.set(SpdyHeaders.HttpNames.VERSION, httpResponse.protocolVersion().text());

        // Transfer the remaining HTTP headers
        Iterator<Entry<CharSequence, CharSequence>> itr = httpHeaders.iteratorCharSequence();
        while (itr.hasNext()) {
            Map.Entry<CharSequence, CharSequence> entry = itr.next();
            final CharSequence headerName =
                    headersToLowerCase ? AsciiString.of(entry.getKey()).toLowerCase() : entry.getKey();
            spdyHeadersFrame.headers().add(headerName, entry.getValue());
        }

        currentStreamId = streamId;
        spdyHeadersFrame.setLast(isLast(httpResponse));

        return spdyHeadersFrame;
    }

    
Checks if the given HTTP message should be considered as a last SPDY frame.
Params:
httpMessage – check this HTTP message
Returns:
whether the given HTTP message should generate a last SPDY frame./**
     * Checks if the given HTTP message should be considered as a last SPDY frame.
     *
     * @param httpMessage check this HTTP message
     * @return whether the given HTTP message should generate a <em>last</em> SPDY frame.
     */
    private static boolean isLast(HttpMessage httpMessage) {
        if (httpMessage instanceof FullHttpMessage) {
            FullHttpMessage fullMessage = (FullHttpMessage) httpMessage;
            if (fullMessage.trailingHeaders().isEmpty() && !fullMessage.content().isReadable()) {
                return true;
            }
        }

        return false;
    }
}