/*
    * Copyright 2013 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.channel;
  
  import io.netty.util.ReferenceCountUtil;
  import io.netty.util.internal.TypeParameterMatcher;
  
  /**
   * {@link ChannelInboundHandlerAdapter} which allows to explicit only handle a specific type of messages.
   *
   * For example here is an implementation which only handle {@link String} messages.
   *
   * <pre>
   *     public class StringHandler extends
   *             {@link SimpleChannelInboundHandler}&lt;{@link String}&gt; {
   *
   *         {@code @Override}
   *         protected void channelRead0({@link ChannelHandlerContext} ctx, {@link String} message)
   *                 throws {@link Exception} {
   *             System.out.println(message);
   *         }
   *     }
   * </pre>
   *
   * Be aware that depending of the constructor parameters it will release all handled messages by passing them to
   * {@link ReferenceCountUtil#release(Object)}. In this case you may need to use
   * {@link ReferenceCountUtil#retain(Object)} if you pass the object to the next handler in the {@link ChannelPipeline}.
   */
  public abstract class SimpleChannelInboundHandler<I> extends ChannelInboundHandlerAdapter {
  
      private final TypeParameterMatcher matcher;
      private final boolean autoRelease;
  
      /**
       * see {@link #SimpleChannelInboundHandler(boolean)} with {@code true} as boolean parameter.
       */
      protected SimpleChannelInboundHandler() {
          this(true);
      }
  
      /**
       * Create a new instance which will try to detect the types to match out of the type parameter of the class.
       *
       * @param autoRelease   {@code true} if handled messages should be released automatically by passing them to
       *                      {@link ReferenceCountUtil#release(Object)}.
       */
      protected SimpleChannelInboundHandler(boolean autoRelease) {
          matcher = TypeParameterMatcher.find(this, SimpleChannelInboundHandler.class, "I");
          this.autoRelease = autoRelease;
      }
  
      /**
       * see {@link #SimpleChannelInboundHandler(Class, boolean)} with {@code true} as boolean value.
       */
      protected SimpleChannelInboundHandler(Class<? extends I> inboundMessageType) {
          this(inboundMessageType, true);
      }
  
      /**
       * Create a new instance
       *
       * @param inboundMessageType    The type of messages to match
       * @param autoRelease           {@code true} if handled messages should be released automatically by passing them to
       *                              {@link ReferenceCountUtil#release(Object)}.
       */
      protected SimpleChannelInboundHandler(Class<? extends I> inboundMessageType, boolean autoRelease) {
          matcher = TypeParameterMatcher.get(inboundMessageType);
          this.autoRelease = autoRelease;
      }
  
      /**
       * Returns {@code true} if the given message should be handled. If {@code false} it will be passed to the next
       * {@link ChannelInboundHandler} in the {@link ChannelPipeline}.
       */
      public boolean acceptInboundMessage(Object msg) throws Exception {
          return matcher.match(msg);
      }
  
      @Override
      public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
          boolean release = true;
          try {
              if (acceptInboundMessage(msg)) {
                  @SuppressWarnings("unchecked")
                  I imsg = (I) msg;
                  channelRead0(ctx, imsg);
             } else {
                 release = false;
                 ctx.fireChannelRead(msg);
             }
         } finally {
             if (autoRelease && release) {
                 ReferenceCountUtil.release(msg);
             }
         }
     }
 
     /**
      * Is called for each message of type {@link I}.
      *
      * @param ctx           the {@link ChannelHandlerContext} which this {@link SimpleChannelInboundHandler}
      *                      belongs to
      * @param msg           the message to handle
      * @throws Exception    is thrown if an error occurred
      */
     protected abstract void channelRead0(ChannelHandlerContext ctx, I msg) throws Exception;
 }