agendas: keep stable time on dst change for date time periods (#72508)

chrono/agendas/models.py

@@ -1319,13 +1319,14 @@ class SharedTimePeriod:
         meeting_duration = datetime.timedelta(minutes=meeting_duration)
         duration = datetime.timedelta(minutes=base_duration)
 
-        real_min_datetime = (
-            min_datetime + datetime.timedelta(days=self.weekday - min_datetime.weekday())
-            if not self.date
-            else min_datetime
-        )
-        if real_min_datetime < min_datetime:
-            real_min_datetime += datetime.timedelta(days=7)
+        if not self.date:
+            real_min_datetime = min_datetime + datetime.timedelta(days=self.weekday - min_datetime.weekday())
+            if real_min_datetime < min_datetime:
+                real_min_datetime += datetime.timedelta(days=7)
+        else:
+            real_min_datetime = make_aware(
+                datetime.datetime(day=self.date.day, month=self.date.month, year=self.date.year)
+            )
 
         # make sure datetime in local timezone, it's ABSOLUTELY necessary
         # to have stable event ids in the API.
@@ -1335,10 +1336,7 @@ class SharedTimePeriod:
         event_datetime = make_aware(make_naive(real_min_datetime)).replace(
             hour=self.start_time.hour, minute=self.start_time.minute, second=0, microsecond=0
         )
-        if self.date:
-            event_datetime = event_datetime.replace(
-                day=self.date.day, month=self.date.month, year=self.date.year
-            )
+
         # don't start before min_datetime
         event_datetime = max(event_datetime, min_datetime)
 

tests/api/datetimes/test_meetings.py

@@ -2542,3 +2542,33 @@ def test_datetimes_api_meetings_virtual_agenda_date_time_period(app):
     assert [x['datetime'] for x in resp.json['data']] == [
         '2022-10-24 13:00:00',
     ]
+
+
+@pytest.mark.freeze_time('2023-03-01 01:00')
+def test_datetimes_api_meetings_agenda_date_time_period_dst_change(app):
+    agenda = Agenda.objects.create(
+        label='Foo bar', kind='meetings', minimal_booking_delay=0, maximal_booking_delay=60
+    )
+    meeting_type = MeetingType.objects.create(agenda=agenda, label='Plop', duration=30)
+    desk = Desk.objects.create(agenda=agenda, label='desk')
+
+    # DST change happens on 26/03
+    TimePeriod.objects.create(
+        date=datetime.date(2023, 3, 21),
+        start_time=datetime.time(10, 0),
+        end_time=datetime.time(10, 30),
+        desk=desk,
+    )
+    TimePeriod.objects.create(
+        date=datetime.date(2023, 3, 28),
+        start_time=datetime.time(10, 0),
+        end_time=datetime.time(10, 30),
+        desk=desk,
+    )
+    api_url = '/api/agenda/%s/meetings/%s/datetimes/' % (agenda.slug, meeting_type.slug)
+
+    resp = app.get(api_url)
+    assert [x['datetime'] for x in resp.json['data']] == [
+        '2023-03-21 10:00:00',
+        '2023-03-28 10:00:00',
+    ]