/*
 *  Licensed to the Apache Software Foundation (ASF) under one
 *  or more contributor license agreements.  See the NOTICE file
 *  distributed with this work for additional information
 *  regarding copyright ownership.  The ASF 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.apache.mina.http;

import java.nio.ByteBuffer;
import java.util.HashMap;
import java.util.Map;
import java.util.regex.Pattern;

import org.apache.mina.core.buffer.IoBuffer;
import org.apache.mina.core.session.IoSession;
import org.apache.mina.filter.codec.ProtocolDecoder;
import org.apache.mina.filter.codec.ProtocolDecoderOutput;
import org.apache.mina.http.api.HttpEndOfContent;
import org.apache.mina.http.api.HttpMethod;
import org.apache.mina.http.api.HttpStatus;
import org.apache.mina.http.api.HttpVersion;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

/**
 * The HTTP decoder
 * 
 * @author <a href="http://mina.apache.org">Apache MINA Project</a>
 */
public class HttpServerDecoder implements ProtocolDecoder {
    private static final Logger LOGGER = LoggerFactory.getLogger(HttpServerCodec.class);

    /** Key for decoder current state */
    private static final String DECODER_STATE_ATT = "http.ds";

    /** Key for the partial HTTP requests head */
    private static final String PARTIAL_HEAD_ATT = "http.ph";

    /** Key for the number of bytes remaining to read for completing the body */
    private static final String BODY_REMAINING_BYTES = "http.brb";

    /** Regex to parse HttpRequest Request Line */
    public static final Pattern REQUEST_LINE_PATTERN = Pattern.compile(" ");

    /** Regex to parse out QueryString from HttpRequest */
    public static final Pattern QUERY_STRING_PATTERN = Pattern.compile("\\?");

    /** Regex to parse out parameters from query string */
    public static final Pattern PARAM_STRING_PATTERN = Pattern.compile("\\&|;");

    /** Regex to parse out key/value pairs */
    public static final Pattern KEY_VALUE_PATTERN = Pattern.compile("=");

    /** Regex to parse raw headers and body */
    public static final Pattern RAW_VALUE_PATTERN = Pattern.compile("\\r\\n\\r\\n");

    /** Regex to parse raw headers from body */
    public static final Pattern HEADERS_BODY_PATTERN = Pattern.compile("\\r\\n");

    /** Regex to parse header name and value */
    public static final Pattern HEADER_VALUE_PATTERN = Pattern.compile(":");

    /** Regex to split cookie header following RFC6265 Section 5.4 */
    public static final Pattern COOKIE_SEPARATOR_PATTERN = Pattern.compile(";");

    /**
     * {@inheritDoc}
     */
    @Override
    public void decode(IoSession session, IoBuffer msg, ProtocolDecoderOutput out) {
        DecoderState state = (DecoderState) session.getAttribute(DECODER_STATE_ATT);
        
        if (null == state) {
            session.setAttribute(DECODER_STATE_ATT, DecoderState.NEW);
            state = (DecoderState) session.getAttribute(DECODER_STATE_ATT);
        }
        
        switch (state) {
            case HEAD:
                if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug("decoding HEAD");
                }
                
                // grab the stored a partial HEAD request
                ByteBuffer oldBuffer = (ByteBuffer) session.getAttribute(PARTIAL_HEAD_ATT);
                // concat the old buffer and the new incoming one
                // now let's decode like it was a new message
                msg = IoBuffer.allocate(oldBuffer.remaining() + msg.remaining()).put(oldBuffer).put(msg).flip();
                
            case NEW:
                if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug("decoding NEW");
                }
                
                HttpRequestImpl rq = parseHttpRequestHead(msg.buf());
    
                if (rq == null) {
                    // we copy the incoming BB because it's going to be recycled by the inner IoProcessor for next reads
                    ByteBuffer partial = ByteBuffer.allocate(msg.remaining());
                    partial.put(msg.buf());
                    partial.flip();
                    // no request decoded, we accumulate
                    session.setAttribute(PARTIAL_HEAD_ATT, partial);
                    session.setAttribute(DECODER_STATE_ATT, DecoderState.HEAD);
                    break;
                } else {
                    out.write(rq);
                    // is it a request with some body content ?
                    String contentLen = rq.getHeader("content-length");
    
                    if (contentLen != null) {
                        if (LOGGER.isDebugEnabled()) {
                            LOGGER.debug("found content len : {}", contentLen);
                        }
                        
                        session.setAttribute(BODY_REMAINING_BYTES, Integer.valueOf(contentLen));
                        session.setAttribute(DECODER_STATE_ATT, DecoderState.BODY);
                        // fallthrough, process body immediately
                    } else {
                        if (LOGGER.isDebugEnabled()) {
                            LOGGER.debug("request without content");
                        }
                        
                        session.setAttribute(DECODER_STATE_ATT, DecoderState.NEW);
                        out.write(new HttpEndOfContent());
                        break;
                    }
                }
    
            case BODY:
                if (LOGGER.isDebugEnabled()) {
                    LOGGER.debug("decoding BODY: {} bytes", msg.remaining());
                }
                
                int chunkSize = msg.remaining();
                
                // send the chunk of body
                if (chunkSize != 0) {
                    IoBuffer wb = IoBuffer.allocate(msg.remaining());
                    wb.put(msg);
                    wb.flip();
                    out.write(wb);
                }
                
                msg.position(msg.limit());
                // do we have reach end of body ?
                int remaining = (Integer) session.getAttribute(BODY_REMAINING_BYTES);
                remaining -= chunkSize;
    
                if (remaining <= 0) {
                    if (LOGGER.isDebugEnabled()) {
                        LOGGER.debug("end of HTTP body");
                    }
                    
                    session.setAttribute(DECODER_STATE_ATT, DecoderState.NEW);
                    session.removeAttribute(BODY_REMAINING_BYTES);
                    out.write(new HttpEndOfContent());
                } else {
                    session.setAttribute(BODY_REMAINING_BYTES, Integer.valueOf(remaining));
                }
    
                break;
    
            default:
                throw new HttpException(HttpStatus.CLIENT_ERROR_BAD_REQUEST, "Unknonwn decoder state : " + state);
        }
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void finishDecode(IoSession session, ProtocolDecoderOutput out) throws Exception {
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public void dispose(IoSession session) throws Exception {
    }

    private HttpRequestImpl parseHttpRequestHead(ByteBuffer buffer) {
        String raw = new String(buffer.array(), buffer.position(), buffer.remaining());
        String[] headersAndBody = RAW_VALUE_PATTERN.split(raw, -1);

        if (headersAndBody.length <= 1) {
            // we didn't receive the full HTTP head
            return null;
        }

        String[] headerFields = HEADERS_BODY_PATTERN.split(headersAndBody[0]);
        headerFields = ArrayUtil.dropFromEndWhile(headerFields, "");

        String requestLine = headerFields[0];
        Map<String, String> generalHeaders = new HashMap<>();

        for (String header : headerFields) {
            int firstColon = header.indexOf(':');
            if (firstColon > 0) {
                generalHeaders.put(header.substring(0, firstColon).toLowerCase(),
                        header.substring(firstColon + 1).trim());
            } else {
                generalHeaders.put(header.trim(), "");
            }
        }

        String[] elements = REQUEST_LINE_PATTERN.split(requestLine);
        HttpMethod method = HttpMethod.valueOf(elements[0]);
        HttpVersion version = HttpVersion.fromString(elements[2]);
        String[] pathFrags = QUERY_STRING_PATTERN.split(elements[1]);
        String requestedPath = pathFrags[0];
        String queryString = pathFrags.length == 2 ? pathFrags[1] : "";

        // we put the buffer position where we found the beginning of the HTTP body
        buffer.position(headersAndBody[0].length() + 4);

        return new HttpRequestImpl(version, method, requestedPath, queryString, generalHeaders);
    }
}
