/**
    * This file Copyright (c) 2003-2011 Magnolia International
    * Ltd.  (http://www.magnolia-cms.com). All rights reserved.
    *
    *
    * This file is dual-licensed under both the Magnolia
    * Network Agreement and the GNU General Public License.
    * You may elect to use one or the other of these licenses.
    *
   * This file is distributed in the hope that it will be
   * useful, but AS-IS and WITHOUT ANY WARRANTY; without even the
   * implied warranty of MERCHANTABILITY or FITNESS FOR A
   * PARTICULAR PURPOSE, TITLE, or NONINFRINGEMENT.
   * Redistribution, except as permitted by whichever of the GPL
   * or MNA you select, is prohibited.
   *
   * 1. For the GPL license (GPL), you can redistribute and/or
   * modify this file under the terms of the GNU General
   * Public License, Version 3, as published by the Free Software
   * Foundation.  You should have received a copy of the GNU
   * General Public License, Version 3 along with this program;
   * if not, write to the Free Software Foundation, Inc., 51
   * Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   *
   * 2. For the Magnolia Network Agreement (MNA), this file
   * and the accompanying materials are made available under the
   * terms of the MNA which accompanies this distribution, and
   * is available at http://www.magnolia-cms.com/mna.html
   *
   * Any modifications to this file must keep this entire header
   * intact.
   *
   */
  package info.magnolia.cms.util;
  
  import info.magnolia.context.LifeTimeJCRSessionUtil;
  
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  
  import javax.jcr.RepositoryException;
  import javax.jcr.Session;
  import javax.jcr.Workspace;
  import javax.jcr.observation.Event;
  import javax.jcr.observation.EventIterator;
  import javax.jcr.observation.EventListener;
  import javax.jcr.observation.ObservationManager;
  
  import org.apache.jackrabbit.core.observation.ObservationManagerImpl;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  
  /**
   * Util to register JCR observations. Supports delayed execution of the listener to handle event bursts.
   *
   * @version $Id: ObservationUtil.java 56279 2012-03-28 07:58:23Z ehechinger $
   */
  public class ObservationUtil {
  
      private final static Logger log = LoggerFactory.getLogger(ObservationUtil.class);
  
      private static final int ALL_EVENT_TYPES_MASK = Event.NODE_ADDED | Event.NODE_REMOVED | Event.NODE_MOVED | Event.PROPERTY_ADDED | Event.PROPERTY_CHANGED | Event.PROPERTY_REMOVED;
  
  
      /**
       * Unregisters all EventListeners for the given workspace.
       */
      public static void dispose(String workspace) {
          try {
              ObservationManager om = getObservationManager(workspace);
  
              if(om instanceof ObservationManagerImpl) {
                  ((ObservationManagerImpl)om).dispose();
              } else {
                  log.warn("Observation can not be disposed ");
              }
          } catch (RepositoryException e) {
              log.error("Unable to Unregisters all EventListeners for the following workspace "+workspace, e);
          }
      }
  
  
      /**
       * Registers an EventListener for any node type.
       *
       * @see #registerChangeListener(String,String,boolean,String[],javax.jcr.observation.EventListener)
       */
      public static void registerChangeListener(String workspace, String observationPath, EventListener listener) {
          registerChangeListener(workspace, observationPath, true, listener);
      }
  
      /**
       * Registers an EventListener for any node type.
       *
       * @see #registerChangeListener(String,String,boolean,String[],javax.jcr.observation.EventListener)
       */
      public static void registerChangeListener(String workspace, String observationPath, boolean includeSubnodes, EventListener listener) {
         registerChangeListener(workspace, observationPath, includeSubnodes, (String[]) null, listener);
     }
 
     /**
      * Registers an EventListener for a specific node type.
      *
      * @see #registerChangeListener(String,String,boolean,String[],javax.jcr.observation.EventListener)
      */
     public static void registerChangeListener(String workspace, String observationPath, boolean includeSubnodes, String nodeType, EventListener listener) {
         registerChangeListener(workspace, observationPath, includeSubnodes, new String[] { nodeType }, listener);
     }
 
     /**
      * Registers an EventListener for a specific node type and event types.
      *
      * @see #registerChangeListener(String,String,boolean,String[],int,javax.jcr.observation.EventListener)
      */
     public static void registerChangeListener(String workspace, String observationPath, boolean includeSubnodes, String nodeType, int eventTypesMask, EventListener listener) {
         if (nodeType == null) {
             registerChangeListener(workspace, observationPath, includeSubnodes, (String[]) null, eventTypesMask, listener);
         } else {
             registerChangeListener(workspace, observationPath, includeSubnodes, new String[] { nodeType }, eventTypesMask, listener);
         }
     }
 
     /**
      * Registers an EventListener for a specific set of node types and event types.
      *
      * @see #registerChangeListener(String, String, boolean, String[], int, javax.jcr.observation.EventListener)
      */
     public static void registerChangeListener(String workspace, String observationPath, boolean includeSubnodes, String[] nodeTypes, EventListener listener) {
         registerChangeListener(workspace, observationPath, includeSubnodes, nodeTypes, ALL_EVENT_TYPES_MASK, listener);
     }
 
     /**
      * Register a single event listener, bound to the given path. Be careful
      * that if you observe "/", events are going to be generated for jcr:system,
      * which is "shared" across all workspaces.
      *
      * @param workspace
      * @param observationPath workspace path
      * @param includeSubnodes the isDeep parameter of ObservationManager.addEventListener()
      * @param nodeTypes the node types to filter events for
      * @param eventTypesMask an ORed mask of even types (Event constants)
      * @param listener event listener
      * @see ObservationManager#addEventListener
      * @see Event
      */
     public static void registerChangeListener(String workspace, String observationPath, boolean includeSubnodes, String[] nodeTypes, int eventTypesMask, EventListener listener) {
         log.debug("Registering event listener for path [{}]", observationPath); //$NON-NLS-1$
 
         try {
             ObservationManager observationManager = getObservationManager(workspace);
             if (observationManager == null) {
                 log.error("Unable to add event listeners for " + observationPath); //$NON-NLS-1$
                 throw new IllegalStateException("Observation manager can't be obtained due to invalid session.");
             }
 
             observationManager.addEventListener(listener, eventTypesMask, observationPath, includeSubnodes, null, nodeTypes, false);
         } catch (RepositoryException e) {
             log.error("Unable to add event listeners for " + observationPath, e); //$NON-NLS-1$
         }
     }
 
     public static void registerDeferredChangeListener(String workspace, String observationPath, EventListener listener, long delay, long maxDelay) {
         registerDeferredChangeListener(workspace, observationPath, true, (String[]) null, listener, delay, maxDelay);
     }
 
     public static void registerDeferredChangeListener(String workspace, String observationPath, boolean includeSubnodes, EventListener listener, long delay, long maxDelay) {
         registerDeferredChangeListener(workspace, observationPath, includeSubnodes, (String[]) null, listener, delay, maxDelay);
     }
 
     public static void registerDeferredChangeListener(String workspace, String observationPath, boolean includeSubnodes, String nodeType, EventListener listener, long delay, long maxDelay) {
         registerDeferredChangeListener(workspace, observationPath, includeSubnodes, new String[] { nodeType }, listener, delay, maxDelay);
     }
 
     /**
      * The event firing is deferred in case there is a series of fired events.
      *
      * @return the wrapped EventListener so that one can unregister it.
      */
     public static void registerDeferredChangeListener(String workspace, String observationPath, boolean includeSubnodes, String[] nodeTypes, EventListener listener, long delay, long maxDelay) {
         final EventListener deferredListener = instanciateDeferredEventListener(listener, delay, maxDelay);
         registerChangeListener(workspace, observationPath, includeSubnodes, nodeTypes, deferredListener);
     }
 
     /**
      * Use this and register the returned EventListener with the
      * registerChangeListener() methods, if you need to be able to later
      * unregister your EventListener.
      */
     public static EventListener instanciateDeferredEventListener(EventListener listener, long delay, long maxDelay) {
         return new DeferringEventListener(listener, delay, maxDelay);
     }
 
     public static void unregisterChangeListener(String workspace, EventListener listener) {
         try {
             ObservationManager om = getObservationManager(workspace);
             if (om == null) {
                 // session have been invalidated and Observation manager is disconnected. Nothing to unregister. Bail out.
                 return;
             }
             om.removeEventListener(listener);
         } catch (RepositoryException e) {
             log.error("Unable to remove event listener [" + listener + "] from workspace " + workspace, e);
         }
     }
 
     private static ObservationManager getObservationManager(String workspace) throws RepositoryException {
         Workspace wks = getSession(workspace).getWorkspace();
         return wks.getSession().isLive() ? wks.getObservationManager() : null;
     }
 
     private static Session getSession(String workspace) throws RepositoryException {
         return LifeTimeJCRSessionUtil.getSession(workspace);
     }
 
     /**
      * A listener using an {@link ObservationBasedDelayedExecutor}.
      */
     public static class DeferringEventListener implements EventListener {
 
         private ObservationBasedDelayedExecutor executor;
 
         private EventListener listener;
 
         public DeferringEventListener(EventListener listener, long delay, long maxDelay) {
             this.listener = listener;
             executor = new ObservationBasedDelayedExecutor(listener, delay, maxDelay);
         }
 
         @Override
         public void onEvent(EventIterator events) {
             this.executor.consume(events);
         }
 
         @Override
         public String toString() {
             return super.toString() + ":" + this.listener;
         }
     }
 
     /**
      * Deferred event handling. Uses the DelayedExecutor class.
      */
     public static class ObservationBasedDelayedExecutor {
 
         private final DelayedExecutor delayedExecutor;
         private final List eventsBuffer = new ArrayList();
 
         public ObservationBasedDelayedExecutor(final EventListener listener, long delay, long maxDelay) {
             delayedExecutor = new DelayedExecutor(new Runnable() {
                 @Override
                 public void run() {
                     // during execution consume is blocked
                     synchronized (eventsBuffer) {
                         listener.onEvent(new ListBasedEventIterator(eventsBuffer));
                         eventsBuffer.clear();
                     }
                 }
             }, delay, maxDelay);
         }
 
         protected void consume(EventIterator events) {
             synchronized (this.eventsBuffer) {
                 while (events.hasNext()) {
                     this.eventsBuffer.add(events.next());
                 }
                 delayedExecutor.trigger();
             }
         }
     }
 
     /**
      * List based event iterator. Used to collect events in a list which are
      * later on passed to the listener.
      */
     public static class ListBasedEventIterator implements EventIterator {
 
         private Iterator iterator;
         private List events;
         private int pos = 0;
 
         public ListBasedEventIterator(List events) {
             this.events = events;
             this.iterator = events.iterator();
         }
 
         @Override
         public boolean hasNext() {
             return this.iterator.hasNext();
         }
 
         @Override
         public Object next() {
             pos++;
             return this.iterator.next();
         }
 
         @Override
         public void remove() {
             this.iterator.remove();
         }
 
         @Override
         public Event nextEvent() {
             return (Event) next();
         }
 
         @Override
         public long getPosition() {
             return pos;
         }
 
         @Override
         public long getSize() {
             return events.size();
         }
 
         @Override
         public void skip(long skipNum) {
             for (int i = 0; i < skipNum; i++) {
                 next();
             }
         }
     }
 
 }