/**
    * 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 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.exceptions.DeserializationException;
  import org.apache.hadoop.hbase.protobuf.ProtobufUtil;
  import org.apache.hadoop.hbase.protobuf.generated.LoadBalancerProtos;
  import org.apache.hadoop.hbase.util.Bytes;
  import org.apache.zookeeper.KeeperException;
  
  /**
   * Tracks the load balancer state up in ZK
   */
  @InterfaceAudience.Private
  public class LoadBalancerTracker extends ZooKeeperNodeTracker {
    private static final Log LOG = LogFactory.getLog(LoadBalancerTracker.class);
  
    public LoadBalancerTracker(ZooKeeperWatcher watcher,
        Abortable abortable) {
      super(watcher, watcher.balancerZNode, abortable);
    }
  
    /**
     * Return true if the balance switch is on, false otherwise
     */
    public boolean isBalancerOn() {
      byte [] upData = super.getData(false);
      try {
        // if data in ZK is null, use default of on.
        return upData == null || parseFrom(upData).getBalancerOn();
      } catch (DeserializationException dex) {
        LOG.error("ZK state for LoadBalancer could not be parsed " + Bytes.toStringBinary(upData));
        // return false to be safe.
        return false;
      }
    }
  
    /**
     * Set the balancer on/off
     * @param balancerOn
     * @throws KeeperException
     */
    public void setBalancerOn(boolean balancerOn) throws KeeperException {
    byte [] upData = toByteArray(balancerOn);
      try {
        ZKUtil.setData(watcher, watcher.balancerZNode, upData);
      } catch(KeeperException.NoNodeException nne) {
        ZKUtil.createAndWatch(watcher, watcher.balancerZNode, upData);
      }
      super.nodeDataChanged(watcher.balancerZNode);
    }
  
    private byte [] toByteArray(boolean isBalancerOn) {
      LoadBalancerProtos.LoadBalancerState.Builder builder =
        LoadBalancerProtos.LoadBalancerState.newBuilder();
      builder.setBalancerOn(isBalancerOn);
      return ProtobufUtil.prependPBMagic(builder.build().toByteArray());
    }
  
    private LoadBalancerProtos.LoadBalancerState parseFrom(byte [] pbBytes)
    throws DeserializationException {
      ProtobufUtil.expectPBMagicPrefix(pbBytes);
      LoadBalancerProtos.LoadBalancerState.Builder builder =
        LoadBalancerProtos.LoadBalancerState.newBuilder();
      try {
        int magicLen = ProtobufUtil.lengthOfPBMagic();
        ProtobufUtil.mergeFrom(builder, pbBytes, magicLen, pbBytes.length - magicLen);
      } catch (IOException e) {
        throw new DeserializationException(e);
      }
      return builder.build();
    }
  }