/**
    * This file Copyright (c) 2016-2018 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.observation;
  
  import info.magnolia.cms.util.DelayedExecutor;
  
  import java.util.ArrayList;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Objects;
  
  import javax.jcr.observation.Event;
  import javax.jcr.observation.EventIterator;
  import javax.jcr.observation.EventListener;
  
  /**
   * A listener using an {@link ObservationBasedDelayedExecutor}.
   */
  public 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;
      }
  
      @Override
      public boolean equals(Object o) {
          if (this == o) {
              return true;
          }
          if (o == null || getClass() != o.getClass()) {
              return false;
          }
          DeferringEventListenermagnolia/observation/DeferringEventListener.html#DeferringEventListener">DeferringEventListener that = (DeferringEventListener) o;
          return Objects.equals(listener, that.listener);
      }
  
      @Override
      public int hashCode() {
          return Objects.hash(listener);
      }
  
      /**
       * Deferred event handling. Uses the DelayedExecutor class.
       */
      private static class ObservationBasedDelayedExecutor {
  
          private final DelayedExecutor delayedExecutor;
          private final List<Event> 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.nextEvent());
                 }
                 delayedExecutor.trigger();
             }
         }
     }
 
     /**
      * List based event iterator. Used to collect events in a list which are
      * later on passed to the listener.
      */
     private 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();
             }
         }
     }
 }