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   /*
    * 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:
    *
    *   https://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 {@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.
       */
      protected MessageToMessageCodec() {
          inboundMsgMatcher = TypeParameterMatcher.find(this, MessageToMessageCodec.class, "INBOUND_IN");
          outboundMsgMatcher = TypeParameterMatcher.find(this, MessageToMessageCodec.class, "OUTBOUND_IN");
      }
  
      /**
       * 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 {@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 {@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 MessageToMessageEncoder#encode(ChannelHandlerContext, Object, List)
      */
     protected abstract void encode(ChannelHandlerContext ctx, OUTBOUND_IN msg, List<Object> out)
             throws Exception;
 
     /**
      * @see MessageToMessageDecoder#decode(ChannelHandlerContext, Object, List)
      */
     protected abstract void decode(ChannelHandlerContext ctx, INBOUND_IN msg, List<Object> out)
             throws Exception;
 }