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/*
 * Copyright (C) 2012-2016 Facebook, Inc.
 *
 * Licensed 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 com.facebook.nifty.client;

import org.apache.thrift.transport.TTransport;
import org.apache.thrift.transport.TTransportException;
import org.jboss.netty.buffer.ChannelBuffer;
import org.jboss.netty.buffer.ChannelBuffers;
import org.jboss.netty.channel.Channel;
import org.jboss.netty.channel.ChannelDownstreamHandler;
import org.jboss.netty.channel.ChannelEvent;
import org.jboss.netty.channel.ChannelFuture;
import org.jboss.netty.channel.ChannelFutureListener;
import org.jboss.netty.channel.ChannelHandlerContext;
import org.jboss.netty.channel.ChannelStateEvent;
import org.jboss.netty.channel.ChannelUpstreamHandler;
import org.jboss.netty.channel.ExceptionEvent;
import org.jboss.netty.channel.MessageEvent;

import javax.annotation.concurrent.NotThreadSafe;
import java.io.Closeable;
import java.util.Queue;
import java.util.concurrent.ConcurrentLinkedQueue;

/**
 * This already has a built in TFramedTransport. No need to wrap.
 */
@NotThreadSafe
class TNiftyAsyncClientTransport extends TTransport
        implements ChannelUpstreamHandler, ChannelDownstreamHandler, Closeable
{
    private static final int DEFAULT_BUFFER_SIZE = 1024;
    // this is largely a guess. there shouldn't really be more than 2 write buffers at any given time.
    private static final int MAX_BUFFERS_IN_QUEUE = 3;
    private final Channel channel;
    private final Queue writeBuffers;
    private volatile TNiftyClientListener listener;

    public TNiftyAsyncClientTransport(Channel channel)
    {
        this.channel = channel;
        this.writeBuffers = new ConcurrentLinkedQueue();
    }

    public void setListener(TNiftyClientListener listener)
    {
        this.listener = listener;
    }

    @Override
    public boolean isOpen()
    {
        return channel.isOpen();
    }

    @Override
    public void open()
            throws TTransportException
    {
        // no-op
    }

    @Override
    public void close()
    {
        channel.close();
    }

    @Override
    public int read(byte[] bytes, int offset, int length)
            throws TTransportException
    {
        throw new UnsupportedOperationException();
    }

    @Override
    public void write(byte[] bytes, int offset, int length)
            throws TTransportException
    {
        getWriteBuffer().writeBytes(bytes, offset, length);
    }

    @Override
    public void flush()
            throws TTransportException
    {
        // all these is to re-use the write buffer. We can only clear
        // and re-use a write buffer when the write operation completes,
        // which is an async operation in netty. the future listener
        // down here will be invoked by Netty I/O thread.
        if (!writeBuffers.isEmpty()) {
            final ChannelBuffer channelBuffer = writeBuffers.remove();
            channel.write(channelBuffer).addListener(
                    new ChannelFutureListener()
                    {
                        @Override
                        public void operationComplete(ChannelFuture future)
                                throws Exception
                        {
                            if (future.isSuccess()) {
                                channelBuffer.clear();
                                if (writeBuffers.size() < MAX_BUFFERS_IN_QUEUE) {
                                    writeBuffers.add(channelBuffer);
                                }
                            }
                        }
                    }
            );
        }
    }

    @Override
    public void handleUpstream(ChannelHandlerContext ctx, ChannelEvent e)
            throws Exception
    {
        if (e instanceof MessageEvent) {
            messageReceived(ctx, (MessageEvent) e);
        }
        else if (e instanceof ChannelStateEvent) {
            ChannelStateEvent evt = (ChannelStateEvent) e;
            switch (evt.getState()) {
                case OPEN:
                    if (Boolean.FALSE.equals(evt.getValue())) {
                        listener.onChannelClosedOrDisconnected(ctx.getChannel());
                    }
                    break;
                case CONNECTED:
                    if (evt.getValue() == null) {
                        listener.onChannelClosedOrDisconnected(ctx.getChannel());
                    }
                    break;
                default:
                    break;
            }
        }
        else if (e instanceof ExceptionEvent) {
            listener.onExceptionEvent((ExceptionEvent) e);
        }
        ctx.sendUpstream(e);
        // for all other stuff we drop it on the floor
    }

    private void messageReceived(ChannelHandlerContext ctx, MessageEvent e)
    {
        if (e.getMessage() instanceof ChannelBuffer && listener != null) {
            listener.onFrameRead(ctx.getChannel(), (ChannelBuffer) e.getMessage());
        }
        // drop it
    }

    @Override
    public void handleDownstream(ChannelHandlerContext ctx, ChannelEvent e)
            throws Exception
    {
        ctx.sendDownstream(e);
    }

    public ChannelBuffer getWriteBuffer()
    {
        if (writeBuffers.isEmpty()) {
            writeBuffers.add(ChannelBuffers.dynamicBuffer(DEFAULT_BUFFER_SIZE));
        }
        return writeBuffers.peek();
    }
}