Use static GUIDs in the frab schedule, when possible

wafer/schedule/models.py

@@ -356,8 +356,17 @@ def get_duration_minutes(self):
 
     @property
     def guid(self):
-        """Return a GUID for the ScheduleItem (for frab xml)"""
-        hmac = salted_hmac('wafer-event-uuid', str(self.pk))
+        """Return a GUID for the ScheduleItem (for frab xml)
+
+        We return static GUIDs across re-scheduling, when possible.
+        """
+        if self.talk:
+            id_ = 'talk:' + str(self.talk.pk)
+        elif self.page and self.page.scheduleitem_set.count() == 1:
+            id_ = 'page:' + str(self.page.pk)
+        else:
+            id_ = 'schedule_item:' + str(self.pk)
+        hmac = salted_hmac('wafer-event-uuid', id_)
         return UUID(bytes=hmac.digest()[:16])
 
 

wafer/schedule/templates/wafer.schedule/penta_schedule.xml

@@ -28,7 +28,9 @@
               {# this is more than a little horrible, but will do for testing #}
               {% for row_venue, items in row.items.items %}
                 {% if row_venue == venue and items.item %}
-                  {# The event id is the ScheduleItem pk, which should be unique enough #}
+                  {# The event id is the ScheduleItem pk, which should be unique #}
+                  {# enough, but changes if the event is rescheduled. #}
+                  {# Talks' guid will be stable across re-scheduling. #}
                   <event id="{{ items.item.pk }}" guid="{{ items.item.guid }}">
                     <date>{{ row.start_time.isoformat }}</date>
                     <start>{{ row.start_time|time:"H:i" }}</start>

wafer/schedule/tests/test_models.py

@@ -471,3 +471,34 @@ def test_slot_save_prev_next(self):
                 # No other items should have changed, as time changes don't
                 # cascade that way
                 self.assertEqual(item.last_updated, update_times[item.pk])
+
+
+class ScheduleItemGUIDTests(TestCase):
+    def setUp(self):
+        venue1 = Venue.objects.create(order=1, name='Venue 1')
+        self.venues = [venue1]
+
+    def test_unique_guid(self):
+        """Test that the all guids are unique."""
+        pages = make_pages(2)
+        items = make_items(self.venues * 2, pages)
+
+        guids = set(item.guid for item in items)
+        self.assertEqual(len(guids), len(items))
+
+    def test_rescheduled_page_keeps_guid(self):
+        """A page that's in the schedule once keeps its guid when rescheduled"""
+        pages = make_pages(2)
+        items = make_items(self.venues * 2, pages)
+        guid = items[0].guid
+        # Reschedule
+        for item in items:
+            item.delete()
+        items = make_items(self.venues, pages)
+        self.assertEqual(guid, items[0].guid)
+
+    def test_double_scheduled_page_has_unique_guid(self):
+        """A page that's in the schedule twice has a unique GUID per instance"""
+        pages = make_pages(1)
+        items = make_items(self.venues * 2, pages * 2)
+        self.assertNotEqual(items[0].guid, items[1].guid)