package org.apache.helix;
   
   /*
    * 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.util.ArrayList;
  import java.util.Iterator;
  import java.util.concurrent.ConcurrentLinkedQueue;
  import java.util.concurrent.atomic.AtomicBoolean;
  import java.util.concurrent.atomic.AtomicReference;
  
  import org.I0Itec.zkclient.exception.ZkNoNodeException;
  import org.apache.log4j.Logger;
  
  // TODO: move to mananger.zk
  public class GroupCommit
  { 
    private static Logger  LOG = Logger.getLogger(GroupCommit.class);
    private static class Queue
    {
      final AtomicReference<Thread>      _running = new AtomicReference<Thread>();
      final ConcurrentLinkedQueue<Entry> _pending = new ConcurrentLinkedQueue<Entry>();
    }
  
    private static class Entry
    {
      final String   _key;
      final ZNRecord _record;
      AtomicBoolean  _sent = new AtomicBoolean(false);
  
      Entry(String key, ZNRecord record)
      {
        _key = key;
        _record = record;
      }
    }
  
    private final Queue[]               _queues = new Queue[100];
    
    // potential memory leak if we add resource and remove resource
    // TODO: move the cache logic to data accessor
  //  private final Map<String, ZNRecord> _cache  = new ConcurrentHashMap<String, ZNRecord>();
  
    
    public GroupCommit()
    {
      // Don't use Arrays.fill();
      for (int i = 0; i < _queues.length; ++i)
      {
        _queues[i] = new Queue();
      }
    }
  
    private Queue getQueue(String key)
    {
      return _queues[(key.hashCode() & Integer.MAX_VALUE) % _queues.length];
    }
  
    public boolean commit(BaseDataAccessor<ZNRecord> accessor, int options, String key, ZNRecord record)
    {
      Queue queue = getQueue(key);
      Entry entry = new Entry(key, record);
  
      queue._pending.add(entry);
  
      while (!entry._sent.get())
      {
        if (queue._running.compareAndSet(null, Thread.currentThread()))
        {
          ArrayList<Entry> processed = new ArrayList<Entry>();
          try
          {
            if (queue._pending.peek() == null)
              return true;
  
            // remove from queue
            Entry first = queue._pending.poll();
            processed.add(first);
  
            String mergedKey = first._key;
  //          ZNRecord merged = _cache.get(mergedKey);
            ZNRecord merged = null;
            
           try
           {
             // accessor will fallback to zk if not found in cache
             merged = accessor.get(mergedKey, null, options);
           }
           catch (ZkNoNodeException e)
           {
             // OK.
           }
           
           /**
            * If the local cache does not contain a value, need to check if there is a 
            * value in ZK; use it as initial value if exists
            */
           if (merged == null)
           {
 //            ZNRecord valueOnZk = null;
 //            try
 //            {
 //              valueOnZk = accessor.get(mergedKey, null, 0);
 //            }
 //            catch(Exception e)
 //            {
 //              LOG.info(e);
 //            }
 //            if(valueOnZk != null)
 //            {
 //              merged = valueOnZk;
 //              merged.merge(first._record);
 //            }
 //            else // Zk path has null data. use the first record as initial record.
             {
               merged = new ZNRecord(first._record);
             }
           }
           else
           {
             merged.merge(first._record);
           }
           Iterator<Entry> it = queue._pending.iterator();
           while (it.hasNext())
           {
             Entry ent = it.next();
             if (!ent._key.equals(mergedKey))
               continue;
             processed.add(ent);
             merged.merge(ent._record);
             // System.out.println("After merging:" + merged);
             it.remove();
           }
           // System.out.println("size:"+ processed.size());
           accessor.set(mergedKey, merged, options);
           // accessor.set(mergedKey, merged, BaseDataAccessor.Option.PERSISTENT);
           // _cache.put(mergedKey, merged);
         }
         finally
         {
           queue._running.set(null);
           for (Entry e : processed)
           {
             synchronized (e)
             {
               e._sent.set(true);
               e.notify();
             }
           }
         }
       }
       else
       {
         synchronized (entry)
         {
           try
           {
             entry.wait(10);
           }
           catch (InterruptedException e)
           {
             e.printStackTrace();
             return false;
           }
         }
       }
     }
     return true;
   }
 
 }