/**
 * Copyright 2010 The Apache Software Foundation
 *
 * 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;

import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.hbase.zookeeper.ZooKeeperNodeTracker;
import org.apache.hadoop.hbase.zookeeper.ZooKeeperWatcher;

/**
 * Manages the location of the current active Master for this RegionServer.
 * <p>
 * Listens for ZooKeeper events related to the master address. The node
 * <code>/master</code> will contain the address of the current master.
 * This listener is interested in
 * <code>NodeDeleted</code> and <code>NodeCreated</code> events on
 * <code>/master</code>.
 * <p>
 * Utilizes {@link ZooKeeperNodeTracker} for zk interactions.
 * <p>
 * You can get the current master via {@link #getMasterAddress()}
 */
public class MasterAddressTracker extends ZooKeeperNodeTracker {
  /**
   * Construct a master address listener with the specified
   * <code>zookeeper</code> reference.
   * <p>
   * This constructor does not trigger any actions, you must call methods
   * explicitly.  Normally you will just want to execute {@link #start()} to
   * begin tracking of the master address.
   *
   * @param watcher zk reference and watcher
   * @param abortable abortable in case of fatal error
   */
  public MasterAddressTracker(ZooKeeperWatcher watcher, Abortable abortable) {
    super(watcher, watcher.masterAddressZNode, abortable);
  }

  /**
   * Get the address of the current master if one is available.  Returns null
   * if no current master.
   * @return Server name or null if timed out.
   */
  public ServerName getMasterAddress() {
    return bytesToServerName(super.getData(false));
  }

  /**
   * Check if there is a master available.
   * @return true if there is a master set, false if not.
   */
  public boolean hasMaster() {
    return super.getData(false) != null;
  }

  /**
   * @param bytes Byte array of {@link ServerName#toString()}
   * @return A {@link ServerName} instance.
   */
  private ServerName bytesToServerName(final byte [] bytes) {
    return bytes == null ? null: ServerName.parseVersionedServerName(bytes);
  }
}