/*
 * (C) 2004 - Geotechnical Software Services
 * 
 * This code 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 code 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 program; if not, write to the Free 
 * Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, 
 * MA  02111-1307, USA.
 */
package no.geosoft.cc.locale;



import java.lang.ref.WeakReference;
import java.util.Collection;
import java.util.Iterator;
import java.util.ArrayList;
import java.util.TimeZone;



/**
 * A manager class for keeping track of a "current" time zone.
 * 
 * Reading times from 3rd party sources:
 *
 * <pre>
 *   DateFormat format = new SimpleDateFormat (pattern);
 *   format.setTimeZone (TimeZone.getTimeZone ([accroding to input format]);
 *   Date time = format.parse (string);
 * </pre>
 *
 * Reading times from GUI:
 *
 * <pre>
 *   DateFormat format = new SimpleDateFormat (pattern);
 *   format.setTimeZone (TimeZone.getTimeZone (TimeZoneManager.getTimeZone());
 *   Date time = format.parse (string);
 * </pre> 
 *
 * Displaying times:
 *
 * <pre> 
 *   Date date;
 *   DateFormat format = new SimpleDateFormat (pattern);
 *   format.setTimeZone (TimeZoneManager.getTimeZone());
 *   System.out.println (format.format (date));
 * </pre>
 * 
 * @author <a href="mailto:jacob.dreyer@geosoft.no">Jacob Dreyer</a>
 */   
public class TimeZoneManager
{
  private TimeZone    timeZone_;
  private Collection  listeners_;   // of WeakReference (TimeZoneListener)
  


  /**
   * Create a time manager with the specified current time zone.
   * 
   * @param timeZone  Current time zone.
   */
  public TimeZoneManager (TimeZone timeZone)
  {
    timeZone_ = timeZone;
  }
  

  
  /**
   * Create a time manager with the default current time zone (UTC).
   */
  public TimeZoneManager()
  {
    this (TimeZone.getTimeZone ("UTC"));
  }
  

  
  /**
   * Return the current time zone.
   * 
   * @return  Current time zone.
   */
  public TimeZone getTimeZone()
  {
    return timeZone_;
  }


  
  /**
   * Set new current time zone and update listeners.
   * 
   * @param timeZone  New current time zone.
   */
  public void setTimeZone (TimeZone timeZone)
  {
    if (timeZone.equals (timeZone_))
      return;
    
    timeZone_ = timeZone;

    // Call listeners
    if (listeners_ != null) {
      for (Iterator i = listeners_.iterator(); i.hasNext(); ) {
        WeakReference reference = (WeakReference) i.next();
        TimeZoneListener listener = (TimeZoneListener) reference.get();
        if (listener == null)
          i.remove();
        else
          listener.timeZoneChanged (timeZone_);
      }
    }
  }


  
  /**
   * Add a time zone listener.
   * 
   * @param timeZoneListener  Listener to add.
   */
  public void addTimeZoneListener (TimeZoneListener timeZoneListener)
  {
    if (listeners_ == null)
      listeners_ = new ArrayList();

    // Check to see if it is there already
    for (Iterator i = listeners_.iterator(); i.hasNext(); ) {
      WeakReference reference = (WeakReference) i.next();
      TimeZoneListener listener = (TimeZoneListener) reference.get();
      if (listener == timeZoneListener)
        return;
    }

    // Add the listener
    listeners_.add (new WeakReference (timeZoneListener));
  }



  /**
   * Remove time zone listener.
   * 
   * @param timeZoneListener  Listener to remove.
   */
  public void removeTimeZoneListener (TimeZoneListener timeZoneListener)
  {
    if (listeners_ == null) return;

    for (Iterator i = listeners_.iterator(); i.hasNext(); ) {
      WeakReference reference = (WeakReference) i.next();
      TimeZoneListener listener = (TimeZoneListener) reference.get();
      if (listener == timeZoneListener) {
        i.remove();
        break;
      }
    }
  }
}