/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF 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.apache.reef.wake.remote.transport.netty;

import io.netty.bootstrap.Bootstrap;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.group.ChannelGroup;
import io.netty.channel.group.DefaultChannelGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.util.concurrent.GlobalEventExecutor;
import org.apache.reef.wake.EStage;
import org.apache.reef.wake.EventHandler;
import org.apache.reef.wake.impl.DefaultThreadFactory;
import org.apache.reef.wake.remote.Encoder;
import org.apache.reef.wake.remote.exception.RemoteRuntimeException;
import org.apache.reef.wake.remote.impl.TransportEvent;
import org.apache.reef.wake.remote.transport.Link;
import org.apache.reef.wake.remote.transport.LinkListener;
import org.apache.reef.wake.remote.transport.Transport;
import org.apache.reef.wake.remote.transport.exception.TransportRuntimeException;

import java.io.IOException;
import java.net.BindException;
import java.net.InetSocketAddress;
import java.net.SocketAddress;
import java.util.Random;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * Messaging transport implementation with Netty
 */
public class NettyMessagingTransport implements Transport {

  private static final String CLASS_NAME = NettyMessagingTransport.class.getName();
  private static final Logger LOG = Logger.getLogger(CLASS_NAME);

  private static final int SERVER_BOSS_NUM_THREADS = 3;
  private static final int SERVER_WORKER_NUM_THREADS = 20;
  private static final int CLIENT_WORKER_NUM_THREADS = 10;
  private static final int PORT_START = 10000;
  private static final int PORT_RANGE = 10000;
  private static final Random randPort = new Random();

  private final ConcurrentMap<SocketAddress, LinkReference> addrToLinkRefMap = new ConcurrentHashMap<>();

  private final EventLoopGroup clientWorkerGroup;
  private final EventLoopGroup serverBossGroup;
  private final EventLoopGroup serverWorkerGroup;

  private final Bootstrap clientBootstrap;
  private final ServerBootstrap serverBootstrap;
  private final Channel acceptor;

  private final ChannelGroup clientChannelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);
  private final ChannelGroup serverChannelGroup = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

  private final int serverPort;
  private final SocketAddress localAddress;

  private final NettyClientEventListener clientEventListener;
  private final NettyServerEventListener serverEventListener;

  private final int numberOfTries;
  private final int retryTimeout;

  /**
   * Constructs a messaging transport
   *
   * @param hostAddress   the server host address
   * @param port          the server listening port; when it is 0, randomly assign a port number
   * @param clientStage   the client-side stage that handles transport events
   * @param serverStage   the server-side stage that handles transport events
   * @param numberOfTries the number of tries of connection
   * @param retryTimeout  the timeout of reconnection
   */
  public NettyMessagingTransport(final String hostAddress, int port,
                                 final EStage<TransportEvent> clientStage,
                                 final EStage<TransportEvent> serverStage,
                                 final int numberOfTries,
                                 final int retryTimeout) {

    if (port < 0) {
      throw new RemoteRuntimeException("Invalid server port: " + port);
    }

    this.numberOfTries = numberOfTries;
    this.retryTimeout = retryTimeout;
    this.clientEventListener = new NettyClientEventListener(this.addrToLinkRefMap, clientStage);
    this.serverEventListener = new NettyServerEventListener(this.addrToLinkRefMap, serverStage);

    this.serverBossGroup = new NioEventLoopGroup(SERVER_BOSS_NUM_THREADS, new DefaultThreadFactory(CLASS_NAME + "ServerBoss"));
    this.serverWorkerGroup = new NioEventLoopGroup(SERVER_WORKER_NUM_THREADS, new DefaultThreadFactory(CLASS_NAME + "ServerWorker"));
    this.clientWorkerGroup = new NioEventLoopGroup(CLIENT_WORKER_NUM_THREADS, new DefaultThreadFactory(CLASS_NAME + "ClientWorker"));

    this.clientBootstrap = new Bootstrap();
    this.clientBootstrap.group(this.clientWorkerGroup)
        .channel(NioSocketChannel.class)
        .handler(new NettyChannelInitializer(new NettyDefaultChannelHandlerFactory("client",
            this.clientChannelGroup, this.clientEventListener)))
        .option(ChannelOption.SO_REUSEADDR, true)
        .option(ChannelOption.SO_KEEPALIVE, true);

    this.serverBootstrap = new ServerBootstrap();
    this.serverBootstrap.group(this.serverBossGroup, this.serverWorkerGroup)
        .channel(NioServerSocketChannel.class)
        .childHandler(new NettyChannelInitializer(new NettyDefaultChannelHandlerFactory("server",
            this.serverChannelGroup, this.serverEventListener)))
        .option(ChannelOption.SO_BACKLOG, 128)
        .option(ChannelOption.SO_REUSEADDR, true)
        .childOption(ChannelOption.SO_KEEPALIVE, true);

    LOG.log(Level.FINE, "Binding to {0}", port);

    Channel acceptor = null;
    try {
      if (port > 0) {
        acceptor = this.serverBootstrap.bind(new InetSocketAddress(hostAddress, port)).sync().channel();
      } else {
        while (acceptor == null) {
          port = randPort.nextInt(PORT_START) + PORT_RANGE;
          LOG.log(Level.FINEST, "Try port {0}", port);
          try {
            acceptor = this.serverBootstrap.bind(new InetSocketAddress(hostAddress, port)).sync().channel();
          } catch (final Exception ex) {
            if (ex instanceof BindException) {
              LOG.log(Level.FINEST, "The port {0} is already bound. Try again", port);
            } else {
              throw ex;
            }
          }
        }
      }
    } catch (final Exception ex) {
      final RuntimeException transportException =
          new TransportRuntimeException("Cannot bind to port " + port);
      LOG.log(Level.SEVERE, "Cannot bind to port " + port, ex);

      this.clientWorkerGroup.shutdownGracefully();
      this.serverBossGroup.shutdownGracefully();
      this.serverWorkerGroup.shutdownGracefully();
      throw transportException;
    }

    this.acceptor = acceptor;
    this.serverPort = port;
    this.localAddress = new InetSocketAddress(hostAddress, this.serverPort);

    LOG.log(Level.FINE, "Starting netty transport socket address: {0}", this.localAddress);
  }

  /**
   * Closes all channels and releases all resources
   */
  @Override
  public void close() throws Exception {

    LOG.log(Level.FINE, "Closing netty transport socket address: {0}", this.localAddress);

    this.clientChannelGroup.close().awaitUninterruptibly();
    this.serverChannelGroup.close().awaitUninterruptibly();
    this.acceptor.close().sync();
    this.clientWorkerGroup.shutdownGracefully();
    this.serverBossGroup.shutdownGracefully();
    this.serverWorkerGroup.shutdownGracefully();

    LOG.log(Level.FINE, "Closing netty transport socket address: {0} done", this.localAddress);
  }

  /**
   * Returns a link for the remote address if cached; otherwise opens, caches and returns
   * When it opens a link for the remote address, only one attempt for the address is made at a given time
   *
   * @param remoteAddr the remote socket address
   * @param encoder    the encoder
   * @param listener   the link listener
   * @return a link associated with the address
   */
  @Override
  public <T> Link<T> open(final SocketAddress remoteAddr, final Encoder<? super T> encoder,
                          final LinkListener<? super T> listener) throws IOException {

    Link<T> link = null;

    for (int i = 0; i < this.numberOfTries; ++i) {
      LinkReference linkRef = this.addrToLinkRefMap.get(remoteAddr);

      if (linkRef != null) {
        link = (Link<T>) linkRef.getLink();
        if (LOG.isLoggable(Level.FINE)) {
          LOG.log(Level.FINE, "Link {0} for {1} found", new Object[]{link, remoteAddr});
        }
        if (link != null) {
          return link;
        }
      }

      LOG.log(Level.FINE, "No cached link for {0} thread {1}",
          new Object[]{remoteAddr, Thread.currentThread()});

      // no linkRef
      final LinkReference newLinkRef = new LinkReference();
      final LinkReference prior = this.addrToLinkRefMap.putIfAbsent(remoteAddr, newLinkRef);
      final AtomicInteger flag = prior != null ?
          prior.getConnectInProgress() : newLinkRef.getConnectInProgress();

      synchronized (flag) {
        if (!flag.compareAndSet(0, 1)) {
          while (flag.get() == 1) {
            try {
              flag.wait();
            } catch (final InterruptedException ex) {
              LOG.log(Level.WARNING, "Wait interrupted", ex);
            }
          }
        }
      }

      linkRef = this.addrToLinkRefMap.get(remoteAddr);
      link = (Link<T>) linkRef.getLink();

      if (link != null) {
        return link;
      }

      ChannelFuture connectFuture = null;
      try {
        connectFuture = this.clientBootstrap.connect(remoteAddr);
        connectFuture.syncUninterruptibly();

        link = new NettyLink<>(connectFuture.channel(), encoder, listener);
        linkRef.setLink(link);

        synchronized (flag) {
          flag.compareAndSet(1, 2);
          flag.notifyAll();
        }
        break;
      } catch (final Exception e) {
        if (e.getClass().getSimpleName().compareTo("ConnectException") == 0) {
          LOG.log(Level.WARNING, "Connection refused. Retry {0} of {1}",
              new Object[]{i + 1, this.numberOfTries});
          synchronized (flag) {
            flag.compareAndSet(1, 0);
            flag.notifyAll();
          }

          if (i < this.numberOfTries) {
            try {
              Thread.sleep(retryTimeout);
            } catch (final InterruptedException interrupt) {
              LOG.log(Level.WARNING, "Thread {0} interrupted while sleeping", Thread.currentThread());
            }
          }
        } else {
          throw e;
        }
      }
    }
    return link;
  }

  /**
   * Returns a link for the remote address if already cached; otherwise, returns null
   *
   * @param remoteAddr the remote address
   * @return a link if already cached; otherwise, null
   */
  public <T> Link<T> get(final SocketAddress remoteAddr) {
    final LinkReference linkRef = this.addrToLinkRefMap.get(remoteAddr);
    return linkRef != null ? (Link<T>) linkRef.getLink() : null;
  }

  /**
   * Gets a server local socket address of this transport
   *
   * @return a server local socket address
   */
  @Override
  public SocketAddress getLocalAddress() {
    return this.localAddress;
  }

  /**
   * Gets a server listening port of this transport
   *
   * @return a listening port number
   */
  @Override
  public int getListeningPort() {
    return this.serverPort;
  }

  /**
   * Registers the exception event handler
   *
   * @param handler the exception event handler
   */
  @Override
  public void registerErrorHandler(final EventHandler<Exception> handler) {
    this.clientEventListener.registerErrorHandler(handler);
    this.serverEventListener.registerErrorHandler(handler);
  }
}