/*
 * 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:
 *
 *   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 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 AbstractMemcacheObjectEncoder that encodes MemcacheMessages. 

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.
/**
 * 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 MemcacheMessage and encode it into a writable ByteBuf. 
Params:
ctx – the channel handler context.
msg – the message to encode.
Returns:
the ByteBuf representation of the message./**
     * 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.
Params:
msg – the object to determine the length of.
Returns:
the determined content length./**
     * 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.
Params:
msg – the object to encode.
Returns:
the encoded object./**
     * 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));
    }

}