/**
    * This file Copyright (c) 2003-2018 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.cms.util;
  
  import info.magnolia.context.MgnlContext;
  import info.magnolia.module.ModuleRegistry;
  import info.magnolia.observation.WorkspaceEventListenerRegistration;
  import info.magnolia.repository.RepositoryConstants;
  
  import java.util.ArrayList;
  import java.util.LinkedHashMap;
  import java.util.List;
  import java.util.Map;
  
  import javax.jcr.Node;
  import javax.jcr.RepositoryException;
  import javax.jcr.Session;
  import javax.jcr.observation.EventListener;
  
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  import com.google.common.collect.Lists;
  
  
  /**
   * 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().
   */
  public abstract class ModuleConfigurationObservingManager extends WorkspaceObservingManager {
  
      private final Logger log = LoggerFactory.getLogger(getClass());
  
      private final String pathWithinModule;
      private final ModuleRegistry moduleRegistry;
      private final Map<String, WorkspaceEventListenerRegistration.Handle> pathToListenerMap = new LinkedHashMap<>();
  
      protected ModuleConfigurationObservingManager(String pathWithinModule, ModuleRegistry moduleRegistry) {
          super(RepositoryConstants.CONFIG, null, true, (String[]) null);
  
          this.pathWithinModule = pathWithinModule;
          this.moduleRegistry = moduleRegistry;
      }
  
      @Override
      protected void registerChangeListener(final EventListener eventListener) {
          for (Map.Entry<String, WorkspaceEventListenerRegistration.Handle> entry : pathToListenerMap.entrySet()) {
              try {
                  WorkspaceEventListenerRegistration.Handle listenerRegistration = WorkspaceEventListenerRegistration.observe(getWorkspace(), entry.getKey(), instantiateEventListener())
                          .withSubNodes(isIncludeSubNodes())
                          .withNodeTypes(getNodeTypes())
                          .withEventTypesMask(getEventTypesMask())
                          .withDelay(getDelay(), getMaxDelay())
                          .register();
                  entry.setValue(listenerRegistration);
              } catch (RepositoryException e) {
                  log.warn("Error occurred during registration of an event listener", e);
              }
          }
      }
  
      @Override
      protected void onStart() {
          // just in case if #start() is invoked multiple times unregister all listeners
          for (WorkspaceEventListenerRegistration.Handle listenerRegistrationHandle : pathToListenerMap.values()) {
              try {
                  listenerRegistrationHandle.unregister();
             } catch (RepositoryException e) {
                 log.error("Unable to remove event listener from workspace {}", getWorkspace(), e);
             }
         }
         pathToListenerMap.clear();
         for (String moduleName : moduleRegistry.getModuleNames()) {
             String path = "/modules/" + moduleName + "/" + pathWithinModule;
             pathToListenerMap.put(path, null);
         }
     }
 
     @Override
     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 {
         // defaults to no action
     }
 
     protected void onRegister(Node node) throws RepositoryException {
         // defaults to no action
     }
 
     protected List<Node> getObservedNodes() throws RepositoryException {
 
         Session session = getSession();
 
         List<Node> nodes = new ArrayList<Node>();
         for (String observedPath : pathToListenerMap.keySet()) {
             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 Lists.newArrayList(pathToListenerMap.keySet());
     }
 
 }