/**
    * This file Copyright (c) 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.ui.contentapp.observation;
  
  import info.magnolia.observation.WorkspaceEventListenerRegistration;
  
  import java.util.Collection;
  import java.util.List;
  import java.util.Map;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.CopyOnWriteArrayList;
  import java.util.function.Consumer;
  import java.util.stream.Stream;
  
  import javax.inject.Singleton;
  import javax.jcr.RepositoryException;
  import javax.jcr.observation.Event;
  import javax.jcr.observation.EventIterator;
  import javax.jcr.observation.EventListener;
  
  import com.google.common.collect.Lists;
  
  import lombok.SneakyThrows;
  
  /**
   * UI agnostic JCR Observation utility.
   */
  @Singleton
  public class JcrObservation {
  
      private final Map<String, DelegatingListener> registrarMap = new ConcurrentHashMap<>();
  
      public void register(Consumer<Stream<Event>> consumer, String workspace) {
          DelegatingListener delegatingListener = registrarMap.get(workspace);
          if (delegatingListener == null) {
              delegatingListener = new DelegatingListener(workspace);
              registrarMap.put(workspace, delegatingListener);
          }
          delegatingListener.addConsumer(consumer);
      }
  
      public void unregister(Consumer<Stream<Event>> consumer, String workspace) {
          DelegatingListener delegatingListener = registrarMap.get(workspace);
          if (delegatingListener != null) {
              delegatingListener.removeConsumer(consumer);
          }
      }
  
      private static class DelegatingListener implements EventListener, WorkspaceEventListenerRegistration.Handle {
          private final Collection<Consumer<Stream<Event>>> listeners = new CopyOnWriteArrayList<>();
          private final WorkspaceEventListenerRegistration.Handle handle;
  
          @SneakyThrows(RepositoryException.class)
          private DelegatingListener(String workspace) {
              handle = WorkspaceEventListenerRegistration
                      .observe(workspace, "/", this)
                      .withDelay(200L, 1000L)
                      .register();
          }
  
          @Override
          public void onEvent(EventIterator events) {
              List<Event> eventList = Lists.newArrayList(() -> events);
              this.listeners.forEach(eventListener -> eventListener.accept(eventList.stream()));
          }
  
  
          @SneakyThrows(RepositoryException.class)
         @Override
         public void unregister() {
             handle.unregister();
         }
 
         private void addConsumer(Consumer<Stream<Event>> consumer) {
             listeners.add(consumer);
         }
 
         private void removeConsumer(Consumer<Stream<Event>> consumer) {
             listeners.remove(consumer);
         }
     }
 }