/**
    * 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 java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  import javax.jcr.Node;
  import javax.jcr.RepositoryException;
  import javax.jcr.Session;
  import javax.jcr.observation.EventIterator;
  import javax.jcr.observation.EventListener;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import info.magnolia.context.MgnlContext;
  import info.magnolia.module.ModuleRegistry;
  import info.magnolia.repository.RepositoryConstants;
  
  
  /**
   * Base class for managers that monitor configuration within modules and react when its changed to reload. Configuration
   * is read from a sub path of each modules configuration node. Subclasses override either reload(List<Node>) or the pair
   * onClear() and onRegister().
   *
   * @version $Id$
   */
  public abstract class ModuleConfigurationObservingManager {
  
      protected final Logger log = LoggerFactory.getLogger(getClass());
  
      private final Object reloadMonitor = new Object();
      private final String pathWithinModule;
      private final ModuleRegistry moduleRegistry;
      private final List<String> observedPaths = new ArrayList<String>();
  
      protected ModuleConfigurationObservingManager(String pathWithinModule, ModuleRegistry moduleRegistry) {
          this.pathWithinModule = pathWithinModule;
          this.moduleRegistry = moduleRegistry;
      }
  
      public void start() {
  
          for (String moduleName : moduleRegistry.getModuleNames()) {
              String path = "/modules/" + moduleName + "/" + pathWithinModule;
              observedPaths.add(path);
          }
  
          final EventListener eventListener = ObservationUtil.instanciateDeferredEventListener(new EventListener() {
  
              @Override
              public void onEvent(EventIterator events) {
                  synchronized (reloadMonitor) {
                      MgnlContext.doInSystemContext(new MgnlContext.VoidOp(){
                          @Override
                          public void doExec() {
                              reload();
                          }
                      }, true);
                  }
              }
          }, 1000, 5000);
  
          for (String observedPath : observedPaths) {
              ObservationUtil.registerChangeListener(RepositoryConstants.CONFIG, observedPath, new EventListener(){
  
                  @Override
                 public void onEvent(EventIterator events) {
                     eventListener.onEvent(events);
                 }
             });
         }
 
         synchronized (reloadMonitor) {
             reload();
         }
     }
 
     protected void reload() {
         try {
             List<Node> nodes = getObservedNodes();
             reload(nodes);
         } catch (RepositoryException e) {
             log.error("Reload of observed nodes failed", e);
         }
     }
 
     protected void reload(List<Node> nodes) throws RepositoryException {
         onClear();
         for (Node node : nodes) {
             try {
                 onRegister(node);
             } catch (Exception e) {
                 log.warn("Failed to reload the node [" + node.getPath() + "]");
             }
         }
     }
 
     protected void onClear() throws RepositoryException {
     }
 
     protected void onRegister(Node node) throws RepositoryException {
     }
 
     private List<Node> getObservedNodes() throws RepositoryException {
 
         Session session = getSession();
 
         List<Node> nodes = new ArrayList<Node>();
         for (String observedPath : observedPaths) {
             try {
                 if (session.nodeExists(observedPath)) {
                     nodes.add(session.getNode(observedPath));
                 }
             } catch (RepositoryException e) {
                 log.error("Failed to acquire node for observed path [" + observedPath + "]", e);
             }
         }
         return nodes;
     }
 
     protected Session getSession() throws RepositoryException {
         return MgnlContext.getSystemContext().getJCRSession(RepositoryConstants.CONFIG);
     }
 
     protected List<String> getObservedPaths() {
         return Collections.unmodifiableList(observedPaths);
     }
 
     /**
      * Returns the object used to synchronize on to keep multiple reload operations to occur at the same time. Useful
      * in subclasses to block calls while the reload is in progress.
      */
     protected Object getReloadMonitor() {
         return reloadMonitor;
     }
 }