/*
 * Copyright (C) 2009 eXo Platform SAS.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */
package org.exoplatform.services.jcr.impl.core;

import org.exoplatform.services.log.ExoLogger;
import org.exoplatform.services.log.Log;

import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

import javax.jcr.Session;

/**
 * A framework for detecting JCR session leaks.
 * 
 * @author <a href="mailto:julien.viet@exoplatform.com">Julien Viet</a>
 * @version $Revision$
 */
public class SessionReference extends WeakReference<Session>
{

   /**
    * The logger instance for this class.
    */
   private static final Log LOG = ExoLogger.getLogger("exo.jcr.component.core.SessionReference");

   //
   private static final int INITIAL_DELAY = 10;

   private static final int DELAY = 15;

   //
   private static ScheduledExecutorService executor;

   private static ConcurrentHashMap<Object, SessionReference> objects;

   private static volatile boolean started = false;

   private static long maxAgeMillis_;

   public static void start(long maxAgeMillis)
   {
      if (!started)
      {
         synchronized (SessionReference.class)
         {
            if (started)
               return;
            if (maxAgeMillis < 0)
            {
               throw new IllegalStateException("Wrong max age value " + maxAgeMillis);
            }
            objects = new ConcurrentHashMap<Object, SessionReference>();
            executor = Executors.newSingleThreadScheduledExecutor();
            executor.scheduleWithFixedDelay(detectorTask, INITIAL_DELAY, DELAY, TimeUnit.SECONDS);
            maxAgeMillis_ = maxAgeMillis;
            started = true;
         }
      }
   }

   public static boolean isStarted()
   {
      return started;
   }

   private static final Runnable detectorTask = new Runnable()
   {
      public void run()
      {
         LOG.info("Starting detector task");

         //
         ArrayList<SessionReference> list;
         synchronized (SessionReference.class)
         {
            list = new ArrayList<SessionReference>(objects.values());
         }

         //
         for (SessionReference ref : list)
         {

            // It is closed we remove it
            if (ref.closed)
            {
               objects.remove(ref.key);
            }
            else
            {
               // We get the maybe null session
               Session session = ref.get();

               //
               String error = null;
               if (session == null)
               {
                  // we can consider it is expired and was not closed
                  error = "garbagednotclosed";
               }
               else if (ref.timestamp < System.currentTimeMillis())
               {
                  // it was not closed but we consider it is way too old
                  error = "expired";
               }

               //
               if (error != null)
               {
                  objects.remove(ref.key);
                  Exception e = new Exception();
                  e.setStackTrace(ref.stack);
                  LOG.error("<" + error + ">");
                  LOG.error(e.getLocalizedMessage(), e);
                  LOG.error("</" + error + ">");
               }
            }
         }
         LOG.info("Finished detector task");
      }
   };

   private final StackTraceElement[] stack = new Exception().getStackTrace();

   private final Object key = new Object();

   private final long timestamp = System.currentTimeMillis() + maxAgeMillis_;

   volatile boolean closed = false;

   SessionReference(Session referent)
   {
      super(referent);
      objects.put(key, this);
   }
}