From b5378b04b3402db5c99aaeaf3db456bbd8c5e684 Mon Sep 17 00:00:00 2001
From: Brian Wilson <brian@edx.org>
Date: Tue, 12 Feb 2013 12:25:11 -0500
Subject: [PATCH] change timer to calculate relative duration in javascript

---
 .../lib/xmodule/xmodule/timelimit_module.py   |  4 ++--
 lms/djangoapps/courseware/views.py            | 19 +++++++++----------
 lms/templates/courseware/courseware.html      | 17 +++++++++--------
 3 files changed, 20 insertions(+), 20 deletions(-)

diff --git a/common/lib/xmodule/xmodule/timelimit_module.py b/common/lib/xmodule/xmodule/timelimit_module.py
index 23ed06eb59..9abb5d183f 100644
--- a/common/lib/xmodule/xmodule/timelimit_module.py
+++ b/common/lib/xmodule/xmodule/timelimit_module.py
@@ -86,8 +86,8 @@ class TimeLimitModule(XModule):
         modified_duration = self._get_accommodated_duration(duration)
         self.ending_at = self.beginning_at + modified_duration
         
-    def get_end_time_in_ms(self):
-        return int(self.ending_at * 1000)
+    def get_remaining_time_in_ms(self):
+        return int((self.ending_at - time()) * 1000)
 
     def get_instance_state(self):
         state = {}
diff --git a/lms/djangoapps/courseware/views.py b/lms/djangoapps/courseware/views.py
index e8b36ecd2a..fb351e1c01 100644
--- a/lms/djangoapps/courseware/views.py
+++ b/lms/djangoapps/courseware/views.py
@@ -177,10 +177,10 @@ def check_for_active_timelimit_module(request, course_id, course):
                     raise Http404("No {0} metadata at this location: {1} ".format('time_expired_redirect_url', location))
                 time_expired_redirect_url = timelimit_descriptor.metadata.get('time_expired_redirect_url')
                 context['time_expired_redirect_url'] = time_expired_redirect_url
-                # Fetch the end time (in GMT) as stored in the module when it was started.
-                # This value should be UTC time as number of milliseconds since epoch.
-                end_date = timelimit_module.get_end_time_in_ms()
-                context['timer_expiration_datetime'] = end_date
+                # Fetch the remaining time relative to the end time as stored in the module when it was started.
+                # This value should be in milliseconds.
+                remaining_time = timelimit_module.get_remaining_time_in_ms()
+                context['timer_expiration_duration'] = remaining_time
                 if 'suppress_toplevel_navigation' in timelimit_descriptor.metadata:
                     context['suppress_toplevel_navigation'] = timelimit_descriptor.metadata['suppress_toplevel_navigation']
                 return_url = reverse('jump_to', kwargs={'course_id':course_id, 'location':location})
@@ -191,7 +191,7 @@ def update_timelimit_module(user, course_id, student_module_cache, timelimit_des
     '''
     Updates the state of the provided timing module, starting it if it hasn't begun.
     Returns dict with timer-related values to enable display of time remaining.
-    Returns 'timer_expiration_datetime' in dict if timer is still active, and not if timer has expired.
+    Returns 'timer_expiration_duration' in dict if timer is still active, and not if timer has expired.
     ''' 
     context = {}
     # determine where to go when the exam ends:
@@ -215,10 +215,9 @@ def update_timelimit_module(user, course_id, student_module_cache, timelimit_des
             instance_module.save()
             
         # the exam has been started, either because the student is returning to the
-        # exam page, or because they have just visited it.  Fetch the end time (in GMT) as stored
-        # in the module when it was started.
-        # This value should be UTC time as number of milliseconds since epoch.
-        context['timer_expiration_datetime'] = timelimit_module.get_end_time_in_ms()
+        # exam page, or because they have just visited it.  Fetch the remaining time relative to the
+        # end time as stored in the module when it was started.
+        context['timer_expiration_duration'] = timelimit_module.get_remaining_time_in_ms()
         # also use the timed module to determine whether top-level navigation is visible:
         if 'suppress_toplevel_navigation' in timelimit_descriptor.metadata:
             context['suppress_toplevel_navigation'] = timelimit_descriptor.metadata['suppress_toplevel_navigation']
@@ -325,7 +324,7 @@ def index(request, course_id, chapter=None, section=None,
             if section_module.category == 'timelimit':
                 timer_context = update_timelimit_module(request.user, course_id, student_module_cache, 
                                                         section_descriptor, section_module)
-                if 'timer_expiration_datetime' in timer_context:
+                if 'timer_expiration_duration' in timer_context:
                     context.update(timer_context)
                 else:
                     # if there is no expiration defined, then we know the timer has expired:
diff --git a/lms/templates/courseware/courseware.html b/lms/templates/courseware/courseware.html
index 72a4b2cae1..fcbc83d815 100644
--- a/lms/templates/courseware/courseware.html
+++ b/lms/templates/courseware/courseware.html
@@ -60,14 +60,12 @@
       });
   </script>
 
-% if timer_expiration_datetime:
+% if timer_expiration_duration:
   <script type="text/javascript">  
     var timer = {
-      timer_inst : null,   
-      get_remaining_secs : function() {
-        // set the end time when the template is rendered.
-        // This value should be UTC time as number of milliseconds since epoch.
-        var endTime = new Date(${timer_expiration_datetime});
+      timer_inst : null,
+      end_time : null,
+      get_remaining_secs : function(endTime) {
         var currentTime = new Date();
         var remaining_secs = Math.floor((endTime - currentTime)/1000);
         return remaining_secs;
@@ -87,13 +85,16 @@
         return remainingTimeString;
       },
       update_time : function(self) {
-        remaining_secs = self.get_remaining_secs();
+        remaining_secs = self.get_remaining_secs(self.end_time);
         if (remaining_secs <= 0) {
           self.end(self);
         }
         $('#exam_timer').text(self.get_time_string(remaining_secs));
       },
       start : function() { var that = this;
+        // set the end time when the template is rendered.
+        // This value should be UTC time as number of milliseconds since epoch.
+        this.end_time = new Date((new Date()).getTime() + ${timer_expiration_duration});
         this.timer_inst = setInterval(function(){ that.update_time(that); }, 1000);
       },
       end : function(self) {
@@ -109,7 +110,7 @@
 
 </%block>
 
-% if timer_expiration_datetime:
+% if timer_expiration_duration:
 <div class="timer-main">
   <div id="timer_wrapper">
     % if timer_navigation_return_url: