/*
    * Copyright 2016 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.buffer.ByteBuf;
  import io.netty.channel.AddressedEnvelope;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPipeline;
  import io.netty.channel.ChannelPromise;
  import io.netty.channel.socket.DatagramPacket;
  import io.netty.util.internal.StringUtil;
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  import java.net.InetSocketAddress;
  import java.net.SocketAddress;
  import java.util.List;
  
  /**
   * An encoder that encodes the content in {@link AddressedEnvelope} to {@link DatagramPacket} using
   * the specified message encoder. E.g.,
   *
   * <pre><code>
   * {@link ChannelPipeline} pipeline = ...;
   * pipeline.addLast("udpEncoder", new {@link DatagramPacketEncoder}(new {@code ProtobufEncoder}(...));
   * </code></pre>
   *
   * Note: As UDP packets are out-of-order, you should make sure the encoded message size are not greater than
   * the max safe packet size in your particular network path which guarantees no packet fragmentation.
   *
   * @param <M> the type of message to be encoded
   */
  public class DatagramPacketEncoder<M> extends MessageToMessageEncoder<AddressedEnvelope<M, InetSocketAddress>> {
  
      private final MessageToMessageEncoder<? super M> encoder;
  
      /**
       * Create an encoder that encodes the content in {@link AddressedEnvelope} to {@link DatagramPacket} using
       * the specified message encoder.
       *
       * @param encoder the specified message encoder
       */
      public DatagramPacketEncoder(MessageToMessageEncoder<? super M> encoder) {
          this.encoder = checkNotNull(encoder, "encoder");
      }
  
      @Override
      public boolean acceptOutboundMessage(Object msg) throws Exception {
          if (super.acceptOutboundMessage(msg)) {
              @SuppressWarnings("rawtypes")
              AddressedEnvelope envelope = (AddressedEnvelope) msg;
              return encoder.acceptOutboundMessage(envelope.content())
                      && (envelope.sender() instanceof InetSocketAddress || envelope.sender() == null)
                      && envelope.recipient() instanceof InetSocketAddress;
          }
          return false;
      }
  
      @Override
      protected void encode(
              ChannelHandlerContext ctx, AddressedEnvelope<M, InetSocketAddress> msg, List<Object> out) throws Exception {
          assert out.isEmpty();
  
          encoder.encode(ctx, msg.content(), out);
          if (out.size() != 1) {
              throw new EncoderException(
                      StringUtil.simpleClassName(encoder) + " must produce only one message.");
          }
          Object content = out.get(0);
          if (content instanceof ByteBuf) {
              // Replace the ByteBuf with a DatagramPacket.
              out.set(0, new DatagramPacket((ByteBuf) content, msg.recipient(), msg.sender()));
          } else {
              throw new EncoderException(
                      StringUtil.simpleClassName(encoder) + " must produce only ByteBuf.");
          }
      }
  
      @Override
      public void bind(ChannelHandlerContext ctx, SocketAddress localAddress, ChannelPromise promise) throws Exception {
          encoder.bind(ctx, localAddress, promise);
      }
  
      @Override
      public void connect(
              ChannelHandlerContext ctx, SocketAddress remoteAddress,
              SocketAddress localAddress, ChannelPromise promise) throws Exception {
         encoder.connect(ctx, remoteAddress, localAddress, promise);
     }
 
     @Override
     public void disconnect(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
         encoder.disconnect(ctx, promise);
     }
 
     @Override
     public void close(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
         encoder.close(ctx, promise);
     }
 
     @Override
     public void deregister(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
         encoder.deregister(ctx, promise);
     }
 
     @Override
     public void read(ChannelHandlerContext ctx) throws Exception {
         encoder.read(ctx);
     }
 
     @Override
     public void flush(ChannelHandlerContext ctx) throws Exception {
         encoder.flush(ctx);
     }
 
     @Override
     public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
         encoder.handlerAdded(ctx);
     }
 
     @Override
     public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
         encoder.handlerRemoved(ctx);
     }
 
     @Override
     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
         encoder.exceptionCaught(ctx, cause);
     }
 
     @Override
     public boolean isSharable() {
         return encoder.isSharable();
     }
 }