/*
    * Copyright 2010 Fraunhofer Gesellschaft, Munich, Germany,
    * for its Fraunhofer Institute for Computer Architecture and Software
    * Technology (FIRST), Berlin, Germany. All rights reserved.
    * http://www.first.fraunhofer.de/
    */
   
   package net.kwfgrid.gwes;
   
  import net.kwfgrid.gwes.exception.DatabaseException;
  import org.apache.log4j.Logger;
  
  /**
   * Manages opens and closes sessions to the remote XML db.
   *
   * @author Andreas Hoheisel
   *         (<a href="http://www.andreas-hoheisel.de">www.andreas-hoheisel.de</a>)
   * @version $Id: XMLDBSessionManager.java 1419 2010-11-01 14:12:17Z hoheisel $
   */
  final class XMLDBSessionManager extends Thread {
  
      /**
       * Timeout in milliseconds for a session.
       */
      private final static int SESSION_TIMEOUT = 1000 * 60;
  
      /**
       * log4j logger
       */
      static final Logger logger = Logger.getLogger(XMLDBSessionManager.class);
  
      /**
       * Admin session object
       */
      public final Object adminLock = new Object();
  
      /**
       * Query session object
       */
      public final Object queryLock = new Object();
  
      /**
       * Admin session id
       */
      private String adminSessionId;
  
      /**
       * Query session id
       */
      private String querySessionId;
  
      /**
       * Admin session timestamp last usage
       */
      private long adminTimestamp;
  
      /**
       * Query session timestamp last usage
       */
      private long queryTimestamp;
  
      private XMLDB xmldb;
  
      static int threadcount = 0;
  
      /**
       * Constructor.
       */
      public XMLDBSessionManager(XMLDB xmldb) throws DatabaseException {
          super("XMLDBSessionManager#" + (++threadcount));
          this.xmldb = xmldb;
          start();
      }
  
      /**
       * Start the thread. Disconnects from old sessions.
       */
      public final void run() {
          logger.info(this + " started ...");
          while (!isInterrupted()) {
              long now = System.currentTimeMillis();
              try {
                  logger.debug("Searching for old sessions");
                  // search for old admin sessions
                  synchronized (adminLock) {
                      if (adminSessionId != null && now - adminTimestamp > SESSION_TIMEOUT) {
                          xmldb.disconnectAdmin(adminSessionId);
                          adminSessionId = null;
                          logger.debug("Admin session disconnected");
                      }
                  }
              } catch (DatabaseException e) {
                  logger.error("exception: " + e, e);
                  synchronized (adminLock) {
                      adminSessionId = null;
                      logger.debug("Admin session destroyed");
                  }
              }
              try {
                 // search for old query sessions
                 synchronized (queryLock) {
                     if (querySessionId != null && now - queryTimestamp > SESSION_TIMEOUT) {
                         xmldb.disconnectQuery(querySessionId);
                         querySessionId = null;
                         logger.debug("Query session disconnected");
                     }
                 }
             } catch (DatabaseException e) {
                 logger.error("exception: " + e, e);
                 synchronized (queryLock) {
                     querySessionId = null;
                     logger.debug("Query session destroyed");
                 }
             }
             try {
                 Thread.sleep(SESSION_TIMEOUT);
             } catch (InterruptedException e1) {
                 interrupt();
             }
         }
     }
 
     /**
      * Returns a valid admin session ID.
      * Reconnects to the XMLDB using the Admin stub if it was disconnected due to timeoutRunning.
      * You should synchronize on the adminLock object before invoking this method.
      *
      * @return The session ID.
      * @throws DatabaseException
      */
     public String getAdminSessionId() throws DatabaseException {
         if (adminSessionId == null) {
             adminSessionId = xmldb.connectAdmin();
         }
         adminTimestamp = System.currentTimeMillis();
         return adminSessionId;
     }
 
     /**
      * Returns a valid query session ID.
      * Reconnects to the XMLDB using the Query stub if it was disconnected due to timeoutRunning.
      * You should synchronize on the queryLock object before invoking this method.
      *
      * @return The session ID.
      * @throws DatabaseException
      */
     public String getQuerySessionId() throws DatabaseException {
         if (querySessionId == null) {
             querySessionId = xmldb.connectQuery();
         }
         queryTimestamp = System.currentTimeMillis();
         return querySessionId;
     }
 
     /**
      * Reset session, e.g., after an exception.
      */
     public void resetSession() {
         // try to disconnect from admin session.
         try {
             synchronized (adminLock) {
                 if (adminSessionId != null) {
                     xmldb.disconnectAdmin(adminSessionId);
                     logger.debug("Admin session disconnected");
                     adminSessionId = null;
                 }
             }
         } catch (DatabaseException e) {
             adminSessionId = null;
         }
 
         // try to disconnect from query session.
         try {
             synchronized (queryLock) {
                 if (querySessionId != null) {
                     xmldb.disconnectQuery(querySessionId);
                     logger.debug("Query session disconnected");
                     querySessionId = null;
                 }
             }
         } catch (DatabaseException e) {
             querySessionId = null;
         }
 
     }
 
 }