/*
    * 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 org.jboss.netty.handler.codec.serialization;
  
  import java.io.ObjectInputStream;
  import java.io.ObjectOutputStream;
  import java.io.OutputStream;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.jboss.netty.buffer.ChannelBuffer;
  import org.jboss.netty.buffer.ChannelBufferFactory;
  import org.jboss.netty.buffer.ChannelBufferOutputStream;
  import org.jboss.netty.buffer.ChannelBuffers;
  import org.jboss.netty.channel.Channel;
  import org.jboss.netty.channel.ChannelHandlerContext;
  import org.jboss.netty.handler.codec.oneone.OneToOneEncoder;
  
  /**
   * An encoder which serializes a Java object into a {@link ChannelBuffer}
   * (interoperability version).
   * <p>
   * This encoder is interoperable with the standard Java object streams such as
   * {@link ObjectInputStream} and {@link ObjectOutputStream}.
   */
  public class CompatibleObjectEncoder extends OneToOneEncoder {
  
      private final AtomicReference<ChannelBuffer> buffer =
          new AtomicReference<ChannelBuffer>();
      private final int resetInterval;
      private volatile ObjectOutputStream oout;
      private int writtenObjects;
  
      /**
       * Creates a new instance with the reset interval of {@code 16}.
       */
      public CompatibleObjectEncoder() {
          this(16); // Reset at every sixteen writes
      }
  
      /**
       * Creates a new instance.
       *
       * @param resetInterval
       *        the number of objects between {@link ObjectOutputStream#reset()}.
       *        {@code 0} will disable resetting the stream, but the remote
       *        peer will be at the risk of getting {@link OutOfMemoryError} in
       *        the long term.
       */
      public CompatibleObjectEncoder(int resetInterval) {
          if (resetInterval < 0) {
              throw new IllegalArgumentException(
                      "resetInterval: " + resetInterval);
          }
          this.resetInterval = resetInterval;
      }
  
      /**
       * Creates a new {@link ObjectOutputStream} which wraps the specified
       * {@link OutputStream}.  Override this method to use a subclass of the
       * {@link ObjectOutputStream}.
       */
      protected ObjectOutputStream newObjectOutputStream(OutputStream out) throws Exception {
          return new ObjectOutputStream(out);
      }
  
      @Override
      protected Object encode(ChannelHandlerContext context, Channel channel, Object msg) throws Exception {
          ChannelBuffer buffer = buffer(context);
          ObjectOutputStream oout = this.oout;
          if (resetInterval != 0) {
              // Resetting will prevent OOM on the receiving side.
              writtenObjects ++;
              if (writtenObjects % resetInterval == 0) {
                  oout.reset();
  
                  // Also discard the byproduct to avoid OOM on the sending side.
                  buffer.discardReadBytes();
              }
          }
          oout.writeObject(msg);
          oout.flush();
  
          ChannelBuffer encoded = buffer.readBytes(buffer.readableBytes());
          return encoded;
      }
  
     private ChannelBuffer buffer(ChannelHandlerContext ctx) throws Exception {
         ChannelBuffer buf = buffer.get();
         if (buf == null) {
             ChannelBufferFactory factory = ctx.getChannel().getConfig().getBufferFactory();
             buf = ChannelBuffers.dynamicBuffer(factory);
             if (buffer.compareAndSet(null, buf)) {
                 boolean success = false;
                 try {
                     oout = newObjectOutputStream(new ChannelBufferOutputStream(buf));
                     success = true;
                 } finally {
                     if (!success) {
                         oout = null;
                     }
                 }
             } else {
                 buf = buffer.get();
             }
         }
         return buf;
     }
 }