/*
 * 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.listener;

import org.exoplatform.container.xml.InitParams;
import org.exoplatform.services.log.ExoLogger;
import org.exoplatform.services.log.Log;
import org.exoplatform.services.naming.InitialContextInitializer;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;

/**
 * Created by The eXo Platform SAS Author : Nhu Dinh Thuan
 * nhudinhthuan@exoplatform.com Apr 6, 2007
 */
public class ListenerService
{
   /** 
    * This executor used for asynchronously event broadcast. 
    */
   private final Executor executor;

   /**
    * Listeners by name map.
    */
   private final Map<String, List<Listener>> listeners_;

   private static final Log log = ExoLogger.getLogger("exo.kernel.component.common.ListenerService");

   /**
    * Construct a listener service.
    */
   public ListenerService()
   {
      listeners_ = new HashMap<String, List<Listener>>();
      executor = Executors.newFixedThreadPool(1, new ListenerThreadFactory());
   }

   /**
    * Construct a listener service.
    */
   public ListenerService(InitialContextInitializer initializer, InitParams params)
   {
      listeners_ = new HashMap<String, List<Listener>>();
      int poolSize = 1;

      if (params != null)
      {
         if (params.getValueParam("asynchPoolSize") != null)
         {

            poolSize = Integer.parseInt(params.getValueParam("asynchPoolSize").getValue());
         }
      }
      executor = Executors.newFixedThreadPool(poolSize, new ListenerThreadFactory());
   }

   /**
    * This method is used to register a {@link Listener} to the events of the same
    * name. It is similar to addListener(listener.getName(), listener)
    * 
    * @param listener the listener to notify any time an even of the same name is
    * triggered
    */
   public void addListener(Listener listener)
   {
      addListener(listener.getName(), listener);
   }

   /**
    * This method is used to register a new {@link Listener}. Any time an
    * event of the given event name has been triggered, the {@link Listener} will be
    * notified.
    * This method will:
    * <ol>
    * <li>Check if it exists a list of listeners that have been registered for the
    * given event name, create a new list if no list exists</li>
    * <li>Add the listener to the list</li>
    * </ol>
    * @param eventName The name of the event to listen to
    * @param listener The Listener to notify any time the event with the given
    * name is triggered
    */
   public void addListener(String eventName, Listener listener)
   {
      // Check is Listener or its superclass asynchronous, if so - wrap it in AsynchronousListener.
      Class listenerClass = listener.getClass();

      do
      {
         if (listenerClass.isAnnotationPresent(Asynchronous.class))
         {
            listener = new AsynchronousListener(listener);
            break;
         }
         else
         {
            listenerClass = listenerClass.getSuperclass();
         }
      }
      while (listenerClass != null);

      List<Listener> list = listeners_.get(eventName);
      if (list == null)
      {
         list = new ArrayList<Listener>();
         listeners_.put(eventName, list);
      }
      list.add(listener);
   }

   /**
    * This method is used to broadcast an event. This method should: 1. Check if
    * there is a list of listener that listen to the event name. 2. If there is a
    * list of listener, create the event object with the given name , source and
    * data 3. For each listener in the listener list, invoke the method
    * onEvent(Event)
    * 
    * @param <S> The type of the source that broacast the event
    * @param <D> The type of the data that the source object is working on
    * @param name The name of the event
    * @param source The source object instance
    * @param data The data object instance
    * @throws Exception if an exception occurs
    */
   final public <S, D> void broadcast(String name, S source, D data) throws Exception
   {
      List<Listener> list = listeners_.get(name);
      if (list == null)
         return;
      for (Listener<S, D> listener : list)
      {
         if (log.isDebugEnabled())
         {
            log.debug("broadcasting event " + name + " on " + listener.getName());
         }

         try
         {
            listener.onEvent(new Event<S, D>(name, source, data));
         }
         catch (Exception e)
         {
            // log exception and keep broadcast events
            log.error("Exception on broadcasting events occures: " + e.getMessage(), e.getCause());
            log.info("Exception occures but keep broadcast events.");
         }
      }
   }

   /**
    * This method is used when a developer want to implement his own event object
    * and broadcast the event. The method should: 1. Check if there is a list of
    * listener that listen to the event name. 2. If there is a list of the
    * listener, ror each listener in the listener list, invoke the method
    * onEvent(Event)
    * 
    * @param <T> The type of the event object, the type of the event object has
    *          to be extended from the Event type
    * @param event The event instance
    * @throws Exception
    */
   final public <T extends Event> void broadcast(T event) throws Exception
   {
      List<Listener> list = listeners_.get(event.getEventName());
      if (list == null)
      {
         return;
      }
      for (Listener listener : list)
      {
         try
         {
            listener.onEvent(event);
         }
         catch (Exception e)
         {
            // log exception and keep broadcast events
            log.error("Exception on broadcasting events occures: " + e.getMessage(), e.getCause());
            log.info("Exception occures but keep broadcast events.");
         }
      }
   }

   /**
    * This AsynchronousListener is a wrapper for original listener, that 
    * executes wrapped listeners onEvent() in separate thread. 
    */
   protected class AsynchronousListener<S, D> extends Listener<S, D>
   {
      private Listener<S, D> listener;

      public AsynchronousListener(Listener<S, D> listener)
      {
         this.listener = listener;
      }

      @Override
      public String getName()
      {
         return listener.getName();
      }

      @Override
      public void setName(String s)
      {
         listener.setName(s);
      }

      @Override
      public String getDescription()
      {
         return listener.getDescription();
      }

      @Override
      public void setDescription(String s)
      {
         listener.setDescription(s);
      }

      @Override
      public void onEvent(Event<S, D> event) throws Exception
      {
         executor.execute(new RunListener<S, D>(listener, event));
      }
   }

   /** 
    * This thread executes listener.onEvent(event) method.
    */
   protected class RunListener<S, D> implements Runnable
   {
      private Listener<S, D> listener;

      private Event<S, D> event;

      public RunListener(Listener<S, D> listener, Event<S, D> event)
      {
         this.listener = listener;
         this.event = event;
      }

      /**
       * {@inheritDoc}
       */
      public void run()
      {
         try
         {
            listener.onEvent(event);
         }
         catch (Exception e)
         {
            // Do not throw exception. Event is asynchronous so just report error.
            // Must say that exception will be ignored even in synchronous events.
            log.error("Exception on broadcasting events occures: " + e.getMessage(), e.getCause());
         }
      }
   }
}
