/*
    * $Header: /cvsroot/jdbforms/dbforms/src/org/dbforms/event/datalist/dao/DataSourceSessionList.java,v 1.2 2005/09/01 19:30:46 hkollmann Exp $
    * $Revision: 1.2 $
    * $Date: 2005/09/01 19:30:46 $
    *
    * DbForms - a Rapid Application Development Framework
    * Copyright (C) 2001 Joachim Peer <joepeer@excite.com>
    *
    * This library is free software; you can redistribute it and/or
   * modify it under the terms of the GNU Lesser General Public
   * License as published by the Free Software Foundation; either
   * version 2.1 of the License, or (at your option) any later version.
   *
   * This library is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   * Lesser General Public License for more details.
   *
   * You should have received a copy of the GNU Lesser General Public
   * License along with this library; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307 USA
   */
  
  package org.dbforms.event.datalist.dao;
  
  import org.apache.commons.logging.Log;
  import org.apache.commons.logging.LogFactory;
  
  import org.dbforms.config.Table;
  
  import java.sql.SQLException;
  
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.Map;
  
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpSessionBindingEvent;
  import javax.servlet.http.HttpSessionBindingListener;
  
  /***
   * Holds a list of DataSourceFactory object in the session context. Needed by
   * the navigation events to store the datasource by a per session mode. So it is
   * possible to reuse the data between different calls and it's not neccessary to
   * refetch again.
   * 
   * @author hkk
   */
  public class DataSourceSessionList implements HttpSessionBindingListener {
  	/*** Hashtable to hold all DataSource objects. Key is queryString. */
  
  	// logging category for this class;
  	private static Log logCat = LogFactory.getLog(DataSourceSessionList.class
  			.getName());
  
  	private Map ht = new HashMap();
  
  	/***
  	 * Private constructor. <br>
  	 * Use <code>getInstance</code> to get an instance of the DataSourceList
  	 * object.
  	 */
  	private DataSourceSessionList() {
  		super();
  	}
  
  	/***
  	 * Returns an unique instance of this class for each session
  	 * 
  	 * @param request
  	 *            the request object
  	 * 
  	 * @return DOCUMENT ME!
  	 */
  	public static synchronized DataSourceSessionList getInstance(
  			HttpServletRequest request) {
  		// try to retrieve an existant dataSourceList object from the session
  		// context;
  		DataSourceSessionList ds = (DataSourceSessionList) request.getSession()
  				.getAttribute(
  						"org.dbforms.event.datalist.dao.DataSourceSessionList");
  
  		// if it does not exist, createn a new one and store
  		// its reference into the session;
  		if (ds == null) {
  			ds = new DataSourceSessionList();
  			request.getSession().setAttribute(
  					"org.dbforms.event.datalist.dao.DataSourceSessionList", ds);
  		}
  
  		return ds;
  	}
  
  	/***
  	 * Get a DataSourceFactory object.
  	 * 
  	 * @param table
  	 *            the table object
  	 * @param request
 	 *            the request object
 	 * 
 	 * @return the DataSourceFactory object related to the input table
 	 */
 	public DataSourceFactory get(Table table, HttpServletRequest request) {
 		synchronized (ht) {
 			DataSourceFactory result = (DataSourceFactory) ht.get(getKey(table,
 					request));
 
 			return result;
 		}
 	}
 
 	/***
 	 * Adds a DataSourceFactory object to the list. If object exists in the
 	 * Hashtable close first!
 	 * 
 	 * @param table
 	 *            the table object
 	 * @param request
 	 *            the request object
 	 * @param ds
 	 *            the DataSourceFactory object to store into the list
 	 * 
 	 * @throws SQLException
 	 *             DOCUMENT ME!
 	 */
 	public void put(Table table, HttpServletRequest request,
 			DataSourceFactory ds) throws SQLException {
 		synchronized (ht) {
 			ht.put(getKey(table, request), ds);
 		}
 	}
 
 	/***
 	 * Remove a DataSource object from the list.
 	 * 
 	 * @param table
 	 *            the table object
 	 * @param request
 	 *            the request object
 	 * 
 	 * @return the DataSource object related to the input table. Note that the
 	 *         returned DataSource object has just been closed by this method.
 	 */
 	public DataSourceFactory remove(Table table, HttpServletRequest request) {
 		synchronized (ht) {
 			DataSourceFactory result = (DataSourceFactory) ht.remove(getKey(
 					table, request));
 
 			if (result != null) {
 				result.close();
 			}
 
 			return result;
 		}
 	}
 
 	/***
 	 * Receive notification that this session will be passivated.
 	 * 
 	 * @param event
 	 *            The session event that has occurred
 	 */
 	public void valueBound(HttpSessionBindingEvent event) {
 	}
 
 	/***
 	 * Receive notification that this session was activated.
 	 * 
 	 * @param event
 	 *            The session event that has occurred
 	 */
 	public void valueUnbound(HttpSessionBindingEvent event) {
 		synchronized (ht) {
 			logCat.info("valueUnbound called");
 
 			Iterator iter = ht.values().iterator();
 
 			while (iter.hasNext()) {
 				Object obj = iter.next();
 				DataSourceFactory qry = (DataSourceFactory) obj;
 				qry.close();
 			}
 
 			ht.clear();
 		}
 	}
 
 	/***
 	 * Get the key string used to retrieve the DataSource object from the
 	 * internal hash table.
 	 * 
 	 * @param table
 	 *            the table object
 	 * @param request
 	 *            the request object
 	 * 
 	 * @return the key string (a.k.a. the queryString) used to retrieve the
 	 *         DataSource object from the internal hash table
 	 */
 	private String getKey(Table table, HttpServletRequest request) {
 		String refSource = request.getRequestURI();
 		refSource = refSource + "?" + table.getName();
 
 		return refSource;
 	}
 
 }