/*
    * 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.giraph.comm.netty;
  
  import java.net.InetSocketAddress;
  import java.util.List;
  import com.google.common.collect.Lists;
  
  import io.netty.channel.Channel;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import org.apache.log4j.Logger;
  
  
  /**
   * Maintains multiple channels and rotates between them.  This is thread-safe.
   */
  public class ChannelRotater {
    /** Logger */
    private static final Logger LOG = Logger.getLogger(ChannelRotater.class);
    /** Index of last used channel */
    private int index = 0;
    /** Channel list */
    private final List<Channel> channelList = Lists.newArrayList();
    /** Task id of this channel */
    private final Integer taskId;
    /** Address these channels are associated with */
    private final InetSocketAddress address;
  
    /**
     * Constructor
     *
     * @param taskId Id of the task these channels as associated with
     * @param address Address these channels are associated with
     */
    public ChannelRotater(Integer taskId, InetSocketAddress address) {
      this.taskId = taskId;
      this.address = address;
    }
  
    public Integer getTaskId() {
      return taskId;
    }
  
    /**
     * Add a channel to the rotation
     *
     * @param channel Channel to add
     */
    public synchronized void addChannel(Channel channel) {
      synchronized (channelList) {
        channelList.add(channel);
      }
    }
  
    /**
     * Get the next channel
     *
     * @return Next channel
     */
    public synchronized Channel nextChannel() {
      if (channelList.isEmpty()) {
        LOG.warn("nextChannel: No channels exist for hostname " +
          address.getHostName());
        return null;
      }
  
      ++index;
      if (index >= channelList.size()) {
        index = 0;
      }
      return channelList.get(index);
    }
  
    /**
     * Remove the a channel
     *
     * @param channel Channel to remove
     * @return Return true if successful, false otherwise
     */
    public synchronized boolean removeChannel(Channel channel) {
      boolean success = channelList.remove(channel);
      if (index >= channelList.size()) {
       index = 0;
     }
     return success;
   }
 
   /**
    * Get the number of channels in this object
    *
    * @return Number of channels
    */
   public synchronized int size() {
     return channelList.size();
   }
 
   /**
    * Close the channels
    *
    * @param channelFutureListener If desired, pass in a channel future listener
    */
   public synchronized void closeChannels(
       ChannelFutureListener channelFutureListener) {
     for (Channel channel : channelList) {
       ChannelFuture channelFuture = channel.close();
       if (channelFutureListener != null) {
         channelFuture.addListener(channelFutureListener);
       }
     }
   }
 
   /**
    * Get a copy of the channels
    *
    * @return Copy of the channels
    */
   public synchronized Iterable<Channel> getChannels() {
     return Lists.newArrayList(channelList);
   }
 }