/** 
   Copyright (c) 2005, Brad Neuberg, bkn3@columbia.edu
   http://codinginparadise.org
   
   Permission is hereby granted, free of charge, to any person obtaining 
   a copy of this software and associated documentation files (the "Software"), 
   to deal in the Software without restriction, including without limitation 
   the rights to use, copy, modify, merge, publish, distribute, sublicense, 
   and/or sell copies of the Software, and to permit persons to whom the 
   Software is furnished to do so, subject to the following conditions:
   
   The above copyright notice and this permission notice shall be 
   included in all copies or substantial portions of the Software.
   
   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, 
   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES 
   OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
   IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY 
   CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT 
   OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR 
   THE USE OR OTHER DEALINGS IN THE SOFTWARE.
   
   The JSON class near the end of this file is
   Copyright 2005, JSON.org
*/

/** An object that provides DHTML history, history data, and bookmarking 
    for AJAX applications. */
window.dhtmlHistory = {
   /** Initializes our DHTML history. You should
       call this after the page is finished loading. */
   /** public */ initialize: function() {
      // only Internet Explorer needs to be explicitly initialized;
      // other browsers don't have its particular behaviors.
      // Basicly, IE doesn't autofill form data until the page
      // is finished loading, which means historyStorage won't
      // work until onload has been fired.
      if (this.isInternetExplorer() == false) {
         return;
      }
         
      // if this is the first time this page has loaded...
      if (historyStorage.hasKey("DhtmlHistory_pageLoaded") == false) {
         this.fireOnNewListener = false;
         this.firstLoad = true;
         historyStorage.put("DhtmlHistory_pageLoaded", true);
      }
      // else if this is a fake onload event
      else {
         this.fireOnNewListener = true;
         this.firstLoad = false;   
      }
   },
             
   /** Adds a history change listener. Note that
       only one listener is supported at this
       time. */
   /** public */ addListener: function(callback) {
      this.listener = callback;
      
      // if the page was just loaded and we
      // should not ignore it, fire an event
      // to our new listener now
      if (this.fireOnNewListener == true) {
         this.fireHistoryEvent(this.currentLocation);
         this.fireOnNewListener = false;
      }
   },
   
   /** public */ add: function(newLocation, historyData) {
      // most browsers require that we wait a certain amount of time before changing the
      // location, such as 200 milliseconds; rather than forcing external callers to use
      // window.setTimeout to account for this to prevent bugs, we internally handle this
      // detail by using a 'currentWaitTime' variable and have requests wait in line
      var self = this;
      var addImpl = function() {
         // indicate that the current wait time is now less
         if (self.currentWaitTime > 0)
            self.currentWaitTime = self.currentWaitTime - self.WAIT_TIME;
            
         // remove any leading hash symbols on newLocation
         newLocation = self.removeHash(newLocation);
         
         // IE has a strange bug; if the newLocation
         // is the same as _any_ preexisting id in the
         // document, then the history action gets recorded
         // twice; throw a programmer exception if there is
         // an element with this ID
         var idCheck = document.getElementById(newLocation);
         if (idCheck != undefined || idCheck != null) {
            var message = 
               "Exception: History locations can not have "
               + "the same value as _any_ id's "
               + "that might be in the document, "
               + "due to a bug in Internet "
               + "Explorer; please ask the "
               + "developer to choose a history "
               + "location that does not match "
               + "any HTML id's in this "
               + "document. The following ID "
               + "is already taken and can not "
               + "be a location: " 
               + newLocation;
               
            throw message; 
         }
         
         // store the history data into history storage
         historyStorage.put(newLocation, historyData);
         
         // indicate to the browser to ignore this upcomming 
         // location change
         self.ignoreLocationChange = true;
 
         // indicate to IE that this is an atomic location change
         // block
         this.ieAtomicLocationChange = true;
                 
         // save this as our current location
         self.currentLocation = newLocation;
         
         // change the browser location
         window.location.hash = newLocation;
         
         // change the hidden iframe's location if on IE
         if (self.isInternetExplorer())
            self.iframe.src = "blank.html?" + newLocation;
            
         // end of atomic location change block
         // for IE
         this.ieAtomicLocationChange = false;
      };

      // now execute this add request after waiting a certain amount of time, so as to
      // queue up requests
      window.setTimeout(addImpl, this.currentWaitTime);
   
      // indicate that the next request will have to wait for awhile
      this.currentWaitTime = this.currentWaitTime + this.WAIT_TIME;
   },
   
   /** public */ isFirstLoad: function() {
      if (this.firstLoad == true) {
         return true;
      }
      else {
         return false;
      }
   },
   
   /** public */ isInternational: function() {
      return false;
   },
   
   /** public */ getVersion: function() {
      return "0.05";
   },
   
   /** Gets the current hash value that is in the browser's
       location bar, removing