/**
 * SessionManager class to maintain the session on the client side and monitor if the network goes down
 * To activate the session manager with session extender, you need to call setExtenderUrl() with the path
 * to the JSON server that will handle the session extension. The JSON server must just return the following JSON:
 *  {
 *      "session_extended": "true"
 *  }
 *  Optionally, it can also return the current date and time in a field called "time".
 */
cambrient.SessionManager = function() {
   var session_extender_url = null;
   
   var self;                              // pointer to instance of this class
   var KEEP_ALIVE_PERIOD_MS = 1000*60*15; // keep session alive every fifteen minutes
   var SERVER_TIMEOUT_MS = 1000*60*29;    // How long before the server communication is pronounced dead 
   var lastServerSighting = 0;            // last time we heard from the server

   function constructorFn() {
      self = this;
   }
   
   // Set the URL to the session extender JSON server (see module documentation above)
   constructorFn.prototype.setExtenderUrl = function(url) {
      session_extender_url = cambrient.contextPath + url;
      if (session_extender_url != null) setTimeout(self.keepAlive, KEEP_ALIVE_PERIOD_MS);
   }
   
   // Keep the session alive by making periodic requests to the server
   constructorFn.prototype.keepAlive = function() {
      if (session_extender_url == null) return; // the application needs to set this in order to activate the session manager
   
      var now = new Date();
      if (lastServerSighting == 0) {
         lastServerSighting = new Date().getTime();
      }
      
      if (now.getTime() - lastServerSighting > SERVER_TIMEOUT_MS) {
         // the connection to the server seems to have died. Warn the user
         cambrient.userMessaging.info('Have not heard from the server in ' + (SERVER_TIMEOUT_MS / (1000*60)) + ' minutes.');
      } 

      if (isFunction(session_extender_url.each)) {
        // array of session extender urls
        session_extender_url.each(function(url) {
            self.ajaxCall(url);
        })
      } else {
        self.ajaxCall(session_extender_url);
      }
      
      setTimeout(self.keepAlive, KEEP_ALIVE_PERIOD_MS);
   }

   // The Ajax call to keep the session alive
   constructorFn.prototype.ajaxCall = function(url) {
      // We do not use the ajax module here because we do not want to use up a connection in it's pool
      new Ajax.Request(
            session_extender_url,  {
            onSuccess: function(reply) {
               self.serverPing(reply);
            },
            onFailure: function(reply) {
               cambrient.userMessaging.error('ERROR!! ' + reply);
            }
         }
      );      
   }

   // Callback for when the server replies
   constructorFn.prototype.serverPing = function(reply) {
      lastServerSighting = new Date().getTime();
   }
      
   return new constructorFn();
}

cambrient.sessionManager = new cambrient.SessionManager();