/**
    * 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.hadoop.hbase.zookeeper;
  
  import java.io.IOException;
  import java.util.List;
  import java.util.NavigableSet;
  import java.util.TreeSet;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  import org.apache.hadoop.hbase.classification.InterfaceAudience;
  import org.apache.hadoop.hbase.Abortable;
  import org.apache.hadoop.hbase.ServerName;
  import org.apache.hadoop.hbase.master.ServerListener;
  import org.apache.hadoop.hbase.master.ServerManager;
  import org.apache.zookeeper.KeeperException;
  
  /**
   * Tracks the list of draining region servers via ZK.
   *
   * <p>This class is responsible for watching for changes to the draining
   * servers list.  It handles adds/deletes in the draining RS list and
   * watches each node.
   *
   * <p>If an RS gets deleted from draining list, we call
   * {@link ServerManager#removeServerFromDrainList(ServerName)}
   *
   * <p>If an RS gets added to the draining list, we add a watcher to it and call
   * {@link ServerManager#addServerToDrainList(ServerName)}
   *
   */
  @InterfaceAudience.Private
  public class DrainingServerTracker extends ZooKeeperListener {
    private static final Log LOG = LogFactory.getLog(DrainingServerTracker.class);
  
    private ServerManager serverManager;
    private final NavigableSet<ServerName> drainingServers = new TreeSet<ServerName>();
    private Abortable abortable;
  
    public DrainingServerTracker(ZooKeeperWatcher watcher,
        Abortable abortable, ServerManager serverManager) {
      super(watcher);
      this.abortable = abortable;
      this.serverManager = serverManager;
    }
  
    /**
     * Starts the tracking of draining RegionServers.
     *
     * <p>All Draining RSs will be tracked after this method is called.
     *
     * @throws KeeperException
     */
    public void start() throws KeeperException, IOException {
      watcher.registerListener(this);
      // Add a ServerListener to check if a server is draining when it's added.
      serverManager.registerListener(
          new ServerListener() {
  
            @Override
            public void serverAdded(ServerName sn) {
              if (drainingServers.contains(sn)){
                serverManager.addServerToDrainList(sn);
              }
            }
  
            @Override
            public void serverRemoved(ServerName serverName) {
              // no-op
            }
          }
      );
      List<String> servers =
        ZKUtil.listChildrenAndWatchThem(watcher, watcher.drainingZNode);
      add(servers);
    }
  
    private void add(final List<String> servers) throws IOException {
      synchronized(this.drainingServers) {
        this.drainingServers.clear();
        for (String n: servers) {
          final ServerName sn = ServerName.valueOf(ZKUtil.getNodeName(n));
          this.drainingServers.add(sn);
         this.serverManager.addServerToDrainList(sn);
         LOG.info("Draining RS node created, adding to list [" +
             sn + "]");
 
       }
     }
   }
 
   private void remove(final ServerName sn) {
     synchronized(this.drainingServers) {
       this.drainingServers.remove(sn);
       this.serverManager.removeServerFromDrainList(sn);
     }
   }
 
   @Override
   public void nodeDeleted(final String path) {
     if(path.startsWith(watcher.drainingZNode)) {
       final ServerName sn = ServerName.valueOf(ZKUtil.getNodeName(path));
       LOG.info("Draining RS node deleted, removing from list [" +
           sn + "]");
       remove(sn);
     }
   }
 
   @Override
   public void nodeChildrenChanged(final String path) {
     if(path.equals(watcher.drainingZNode)) {
       try {
         final List<String> newNodes =
           ZKUtil.listChildrenAndWatchThem(watcher, watcher.drainingZNode);
         add(newNodes);
       } catch (KeeperException e) {
         abortable.abort("Unexpected zk exception getting RS nodes", e);
       } catch (IOException e) {
         abortable.abort("Unexpected zk exception getting RS nodes", e);
       }
     }
   }
 }