/*
    * 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.handler.codec.memcache;
  
  import io.netty.buffer.ByteBuf;
  import io.netty.buffer.Unpooled;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.FileRegion;
  import io.netty.handler.codec.MessageToMessageEncoder;
  import io.netty.util.internal.StringUtil;
  import io.netty.util.internal.UnstableApi;
  
  import java.util.List;
  
  /**
   * A general purpose {@link AbstractMemcacheObjectEncoder} that encodes {@link MemcacheMessage}s.
   * <p/>
   * <p>Note that this class is designed to be extended, especially because both the binary and ascii protocol
   * require different treatment of their messages. Since the content chunk writing is the same for both, the encoder
   * abstracts this right away.</p>
   */
  @UnstableApi
  public abstract class AbstractMemcacheObjectEncoder<M extends MemcacheMessage> extends MessageToMessageEncoder<Object> {
  
      private boolean expectingMoreContent;
  
      @Override
      protected void encode(ChannelHandlerContext ctx, Object msg, List<Object> out) throws Exception {
          if (msg instanceof MemcacheMessage) {
              if (expectingMoreContent) {
                  throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg));
              }
  
              @SuppressWarnings({ "unchecked", "CastConflictsWithInstanceof" })
              final M m = (M) msg;
              out.add(encodeMessage(ctx, m));
          }
  
          if (msg instanceof MemcacheContent || msg instanceof ByteBuf || msg instanceof FileRegion) {
              int contentLength = contentLength(msg);
              if (contentLength > 0) {
                  out.add(encodeAndRetain(msg));
              } else {
                  out.add(Unpooled.EMPTY_BUFFER);
              }
  
              expectingMoreContent = !(msg instanceof LastMemcacheContent);
          }
      }
  
      @Override
      public boolean acceptOutboundMessage(Object msg) throws Exception {
          return msg instanceof MemcacheObject || msg instanceof ByteBuf || msg instanceof FileRegion;
      }
  
      /**
       * Take the given {@link MemcacheMessage} and encode it into a writable {@link ByteBuf}.
       *
       * @param ctx the channel handler context.
       * @param msg the message to encode.
       * @return the {@link ByteBuf} representation of the message.
       */
      protected abstract ByteBuf encodeMessage(ChannelHandlerContext ctx, M msg);
  
      /**
       * Determine the content length of the given object.
       *
       * @param msg the object to determine the length of.
       * @return the determined content length.
       */
      private static int contentLength(Object msg) {
          if (msg instanceof MemcacheContent) {
              return ((MemcacheContent) msg).content().readableBytes();
          }
          if (msg instanceof ByteBuf) {
              return ((ByteBuf) msg).readableBytes();
          }
          if (msg instanceof FileRegion) {
              return (int) ((FileRegion) msg).count();
          }
          throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg));
      }
  
      /**
       * Encode the content, depending on the object type.
       *
      * @param msg the object to encode.
      * @return the encoded object.
      */
     private static Object encodeAndRetain(Object msg) {
         if (msg instanceof ByteBuf) {
             return ((ByteBuf) msg).retain();
         }
         if (msg instanceof MemcacheContent) {
             return ((MemcacheContent) msg).content().retain();
         }
         if (msg instanceof FileRegion) {
             return ((FileRegion) msg).retain();
         }
         throw new IllegalStateException("unexpected message type: " + StringUtil.simpleClassName(msg));
     }
 
 }