//
   //  ========================================================================
   //  Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
   //  ------------------------------------------------------------------------
   //  All rights reserved. This program and the accompanying materials
   //  are made available under the terms of the Eclipse Public License v1.0
   //  and Apache License v2.0 which accompanies this distribution.
   //
   //      The Eclipse Public License is available at
  //      http://www.eclipse.org/legal/epl-v10.html
  //
  //      The Apache License v2.0 is available at
  //      http://www.opensource.org/licenses/apache2.0.php
  //
  //  You may elect to redistribute this code under either of these licenses.
  //  ========================================================================
  //
  
  package org.eclipse.jetty.server.handler;
  
  import java.util.Enumeration;
  import java.util.HashSet;
  import java.util.Set;
  
  import javax.servlet.ServletContextAttributeEvent;
  import javax.servlet.ServletContextAttributeListener;
  import javax.servlet.ServletContextEvent;
  import javax.servlet.ServletContextListener;
  
  import org.eclipse.jetty.util.log.Log;
  import org.eclipse.jetty.util.log.Logger;
  
  /* ------------------------------------------------------------ */
  /** Enable Jetty style JMX MBeans from within a Context 
   */
  public class ManagedAttributeListener implements  ServletContextListener, ServletContextAttributeListener
  {
      private static final Logger LOG = Log.getLogger(ManagedAttributeListener.class);
  
      final Set<String> _managedAttributes=new HashSet<>();
      final ContextHandler _context;
      
      public ManagedAttributeListener(ContextHandler context,String... managedAttributes)
      {
          _context=context;
  
          for (String attr:managedAttributes)
              _managedAttributes.add(attr);
          
          if (LOG.isDebugEnabled())
              LOG.debug("managedAttributes {}",_managedAttributes);
      }
  
      @Override
      public void attributeReplaced(ServletContextAttributeEvent event)
      {
          if (_managedAttributes.contains(event.getName()))
              updateBean(event.getName(),event.getValue(),event.getServletContext().getAttribute(event.getName()));
      }
      
      @Override
      public void attributeRemoved(ServletContextAttributeEvent event)
      {
          if (_managedAttributes.contains(event.getName()))
              updateBean(event.getName(),event.getValue(),null);                    
      }
      
      @Override
      public void attributeAdded(ServletContextAttributeEvent event)
      {
          if (_managedAttributes.contains(event.getName()))
              updateBean(event.getName(),null,event.getValue());    
      }
  
      @Override
      public void contextInitialized(ServletContextEvent event)
      {                 
          // Update existing attributes
          Enumeration<String> e = event.getServletContext().getAttributeNames();
          while (e.hasMoreElements())
          {
              String name = e.nextElement();
              if (_managedAttributes.contains(name))
                  updateBean(name,null,event.getServletContext().getAttribute(name));
          }
      }
      
      @Override
      public void contextDestroyed(ServletContextEvent event)
      {
          Enumeration<String> e = _context.getServletContext().getAttributeNames();
          while (e.hasMoreElements())
          {
              String name = e.nextElement();
              if (_managedAttributes.contains(name))
                  updateBean(name,event.getServletContext().getAttribute(name),null);
          }
      }
      
     protected void updateBean(String name,Object oldBean,Object newBean)
     {
         LOG.info("update {} {}->{} on {}",name,oldBean,newBean,_context);
         if (LOG.isDebugEnabled())
             LOG.debug("update {} {}->{} on {}",name,oldBean,newBean,_context);
         _context.updateBean(oldBean,newBean,false);
     }
 }