/*
 * 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;

import io.netty.channel.ChannelDuplexHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelPromise;
import io.netty.util.ReferenceCounted;
import io.netty.util.internal.TypeParameterMatcher;

import java.util.List;

A Codec for on-the-fly encoding/decoding of message. This can be thought of as a combination of MessageToMessageDecoder and MessageToMessageEncoder. Here is an example of a MessageToMessageCodec which just decode from Integer to Long and encode from Long to Integer. 
 public class NumberCodec extends MessageToMessageCodec<Integer, Long> { @Override public Long decode(ChannelHandlerContext ctx, Integer msg, List<Object> out) throws Exception { out.add(msg.longValue()); } @Override public Integer encode(ChannelHandlerContext ctx, Long msg, List<Object> out) throws Exception { out.add(msg.intValue()); } } 
 Be aware that you need to call ReferenceCounted.retain() on messages that are just passed through if they are of type ReferenceCounted. This is needed as the MessageToMessageCodec will call ReferenceCounted.release() on encoded / decoded messages. /**
 * A Codec for on-the-fly encoding/decoding of message.
 *
 * This can be thought of as a combination of {@link MessageToMessageDecoder} and {@link MessageToMessageEncoder}.
 *
 * Here is an example of a {@link MessageToMessageCodec} which just decode from {@link Integer} to {@link Long}
 * and encode from {@link Long} to {@link Integer}.
 *
 * <pre>
 *     public class NumberCodec extends
 *             {@link MessageToMessageCodec}&lt;{@link Integer}, {@link Long}&gt; {
 *         {@code @Override}
 *         public {@link Long} decode({@link ChannelHandlerContext} ctx, {@link Integer} msg, List&lt;Object&gt; out)
 *                 throws {@link Exception} {
 *             out.add(msg.longValue());
 *         }
 *
 *         {@code @Override}
 *         public {@link Integer} encode({@link ChannelHandlerContext} ctx, {@link Long} msg, List&lt;Object&gt; out)
 *                 throws {@link Exception} {
 *             out.add(msg.intValue());
 *         }
 *     }
 * </pre>
 *
 * Be aware that you need to call {@link ReferenceCounted#retain()} on messages that are just passed through if they
 * are of type {@link ReferenceCounted}. This is needed as the {@link MessageToMessageCodec} will call
 * {@link ReferenceCounted#release()} on encoded / decoded messages.
 */
public abstract class MessageToMessageCodec<INBOUND_IN, OUTBOUND_IN> extends ChannelDuplexHandler {

    private final MessageToMessageEncoder<Object> encoder = new MessageToMessageEncoder<Object>() {

        @Override
        public boolean acceptOutboundMessage(Object msg) throws Exception {
            return MessageToMessageCodec.this.acceptOutboundMessage(msg);
        }

        @Override
        @SuppressWarnings("unchecked")
        protected void encode(ChannelHandlerContext ctx, Object msg, List<Object> out) throws Exception {
            MessageToMessageCodec.this.encode(ctx, (OUTBOUND_IN) msg, out);
        }
    };

    private final MessageToMessageDecoder<Object> decoder = new MessageToMessageDecoder<Object>() {

        @Override
        public boolean acceptInboundMessage(Object msg) throws Exception {
            return MessageToMessageCodec.this.acceptInboundMessage(msg);
        }

        @Override
        @SuppressWarnings("unchecked")
        protected void decode(ChannelHandlerContext ctx, Object msg, List<Object> out) throws Exception {
            MessageToMessageCodec.this.decode(ctx, (INBOUND_IN) msg, out);
        }
    };

    private final TypeParameterMatcher inboundMsgMatcher;
    private final TypeParameterMatcher outboundMsgMatcher;

    
Create a new instance which will try to detect the types to decode and encode out of the type parameter
of the class.
/**
     * Create a new instance which will try to detect the types to decode and encode out of the type parameter
     * of the class.
     */
    protected MessageToMessageCodec() {
        inboundMsgMatcher = TypeParameterMatcher.find(this, MessageToMessageCodec.class, "INBOUND_IN");
        outboundMsgMatcher = TypeParameterMatcher.find(this, MessageToMessageCodec.class, "OUTBOUND_IN");
    }

    
Create a new instance.
Params:
inboundMessageType –    The type of messages to decode
outboundMessageType –   The type of messages to encode/**
     * Create a new instance.
     *
     * @param inboundMessageType    The type of messages to decode
     * @param outboundMessageType   The type of messages to encode
     */
    protected MessageToMessageCodec(
            Class<? extends INBOUND_IN> inboundMessageType, Class<? extends OUTBOUND_IN> outboundMessageType) {
        inboundMsgMatcher = TypeParameterMatcher.get(inboundMessageType);
        outboundMsgMatcher = TypeParameterMatcher.get(outboundMessageType);
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        decoder.channelRead(ctx, msg);
    }

    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        encoder.write(ctx, msg, promise);
    }

    
Returns true if and only if the specified message can be decoded by this codec. 
Params:
msg – the message/**
     * Returns {@code true} if and only if the specified message can be decoded by this codec.
     *
     * @param msg the message
     */
    public boolean acceptInboundMessage(Object msg) throws Exception {
        return inboundMsgMatcher.match(msg);
    }

    
Returns true if and only if the specified message can be encoded by this codec. 
Params:
msg – the message/**
     * Returns {@code true} if and only if the specified message can be encoded by this codec.
     *
     * @param msg the message
     */
    public boolean acceptOutboundMessage(Object msg) throws Exception {
        return outboundMsgMatcher.match(msg);
    }

    
See Also:
encode.encode(ChannelHandlerContext, Object, List)/**
     * @see MessageToMessageEncoder#encode(ChannelHandlerContext, Object, List)
     */
    protected abstract void encode(ChannelHandlerContext ctx, OUTBOUND_IN msg, List<Object> out)
            throws Exception;

    
See Also:
decode.decode(ChannelHandlerContext, Object, List)/**
     * @see MessageToMessageDecoder#decode(ChannelHandlerContext, Object, List)
     */
    protected abstract void decode(ChannelHandlerContext ctx, INBOUND_IN msg, List<Object> out)
            throws Exception;
}