package org.apache.helix.manager.zk;
   
   /*
    * 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.
   */
  
  import java.io.File;
  import java.util.List;
  import java.util.Map;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.locks.ReadWriteLock;
  import java.util.concurrent.locks.ReentrantReadWriteLock;
  
  import org.apache.helix.store.zk.ZNode;
  import org.apache.helix.util.HelixUtil;
  import org.apache.zookeeper.data.Stat;
  
  
  public abstract class Cache<T>
  {
    final ReadWriteLock                    _lock;
    final ConcurrentHashMap<String, ZNode> _cache;
  
    public Cache()
    {
      _lock = new ReentrantReadWriteLock();
      _cache = new ConcurrentHashMap<String, ZNode>();
    }
  
    public void addToParentChildSet(String parentPath, String childName)
    {
      ZNode znode = _cache.get(parentPath);
      if (znode != null)
      {
        znode.addChild(childName);
      }
    }
  
    public void addToParentChildSet(String parentPath, List<String> childNames)
    {
      if (childNames != null && !childNames.isEmpty())
      {
        ZNode znode = _cache.get(parentPath);
        if (znode != null)
        {
          znode.addChildren(childNames);
        }
      }
    }
  
    public void removeFromParentChildSet(String parentPath, String name)
    {
      ZNode zNode = _cache.get(parentPath);
      if (zNode != null)
      {
        zNode.removeChild(name);
      }
    }
  
    public boolean exists(String path)
    {
      return _cache.containsKey(path);
    }
  
    public ZNode get(String path)
    {
      try
      {
        _lock.readLock().lock();
        return _cache.get(path);
      } 
      finally
      {
        _lock.readLock().unlock();
      }
    }
  
    public void lockWrite()
    {
      _lock.writeLock().lock();
    }
  
    public void unlockWrite()
   {
     _lock.writeLock().unlock();
   }
 
   public void lockRead()
   {
     _lock.readLock().lock();
   }
 
   public void unlockRead()
   {
     _lock.readLock().unlock();
   }
 
   public void purgeRecursive(String path)
   {
     try
     {
       _lock.writeLock().lock();
 
       String parentPath = HelixUtil.getZkParentPath(path);
       String name = HelixUtil.getZkName(path);
       removeFromParentChildSet(parentPath, name);
 
       ZNode znode = _cache.remove(path);
       if (znode != null)
       {
         // recursively remove children nodes
         Set<String> childNames = znode.getChildSet();
         for (String childName : childNames)
         {
           String childPath = path + "/" + childName;
           purgeRecursive(childPath);
         }
       }
     }
     finally
     {
       _lock.writeLock().unlock();
     }
   }
   
   public void reset()
   {
     try
     {
       _lock.writeLock().lock();
       _cache.clear();
     } 
     finally
     {
       _lock.writeLock().unlock();
     }
   }
   
   public abstract void update(String path, T data, Stat stat);
   
   public abstract void updateRecursive(String path);
   
   
   // debug
   public Map<String, ZNode> getCache()
   {
     return _cache;
   }
   
 }