In charge of the user's location in the app.

class PlaceController {

 //private static final Logger log = Logger.getLogger(PlaceController.class.getName());

 final EventBus _eventBus;

 Delegate _delegate;
 Place _where = Place.NOWHERE;

//  /**
//   * Legacy method tied to the old location for {@link EventBus}.
//   * 
//   * @deprecated use {@link #PlaceController(EventBus)}
//   */
//  @Deprecated
//  PlaceController(com.google.gwt.event.shared.EventBus _eventBus) {
//    this((EventBus) _eventBus);
//  }

//  /**
//   * Legacy method tied to the old location for {@link EventBus}.
//   * 
//   * @deprecated use {@link #PlaceController(EventBus, Delegate)}
//   */
//  @Deprecated
//  PlaceController(com.google.gwt.event.shared.EventBus _eventBus, Delegate _delegate) {
//    this((EventBus) _eventBus, _delegate);
//  }

 /**
  * Create a new PlaceController.
  * 
  * @param _eventBus the {@link EventBus}
  * @param _delegate the {@link Delegate} in charge of Window-related events
  */
 PlaceController(this._eventBus, [Delegate delegate = null]) {
   if (delegate == null) {
     _delegate = new DefaultDelegate();
   } else {
     _delegate = delegate;
   }
   //
   _delegate.addWindowClosingHandler(new ClosingHandlerAdapter((ClosingEvent event) {
     String warning = maybeGoTo(Place.NOWHERE);
     if (warning != null) {
       event.setMessage(warning);
     }
   }));
 }

 /**
  * Returns the current place.
  * 
  * @return a {@link Place} instance
  */
 Place getWhere() {
   return _where;
 }

 /**
  * Request a change to a new place. It is not a given that we'll actually get
  * there. First a {@link PlaceChangeRequestEvent} will be posted to the event
  * bus. If any receivers post a warning message to that event, it will be
  * presented to the user via {@link Delegate#confirm(String)} (which is
  * typically a call to {@link Window#confirm(String)}). If she cancels, the
  * current location will not change. Otherwise, the location changes and a
  * {@link PlaceChangeEvent} is posted announcing the new place.
  * 
  * @param newPlace a {@link Place} instance
  */
 void goTo(Place newPlace) {
//    log().fine("goTo: " + newPlace);

   if (getWhere() == newPlace) {
//      log().fine("Asked to return to the same place: " + newPlace);
     return;
   }

   String warning = maybeGoTo(newPlace);
   if (warning == null || _delegate.confirm(warning)) {
     _where = newPlace;
     _eventBus.fireEvent(new PlaceChangeEvent(newPlace));
   }
 }

//  /**
//   * Visible for testing.
//   */
//  Logger log() {
//    return log;
//  }

 String maybeGoTo(Place newPlace) {
   PlaceChangeRequestEvent willChange = new PlaceChangeRequestEvent(newPlace);
   _eventBus.fireEvent(willChange);
   String warning = willChange.getWarning();
   return warning;
 }
}