Fix getting service IDs for status aggregation

Addresses [1].

Previously the query would always use UTC midnight, even after we
had switched to BST (+1h). We store timestamps as naive UTC in our
DB - without a timezone - but we want the query to work in terms
of GMT / BST so we adjust for that - BST midnight is 11PM in UTC.

[1]: https://github.com/alphagov/notifications-api/pull/3437#discussion_r791998690

app/dao/notifications_dao.py

@@ -46,7 +46,11 @@ from app.models import (
     NotificationHistory,
     ProviderDetails,
 )
-from app.utils import escape_special_characters, midnight_n_days_ago
+from app.utils import (
+    escape_special_characters,
+    get_london_midnight_in_utc,
+    midnight_n_days_ago,
+)
 
 
 def dao_get_last_date_template_was_used(template_id, service_id):
@@ -797,6 +801,9 @@ def get_service_ids_with_notifications_before(notification_type, timestamp):
 
 
 def get_service_ids_with_notifications_on_date(notification_type, date):
+    start_date = get_london_midnight_in_utc(date)
+    end_date = get_london_midnight_in_utc(date + timedelta(days=1))
+
     return {
         row.service_id
         for row in db.session.query(
@@ -804,7 +811,7 @@ def get_service_ids_with_notifications_on_date(notification_type, date):
         ).filter(
             Notification.notification_type == notification_type,
             # using >= + < is much more efficient than date(created_at)
-            Notification.created_at >= date,
-            Notification.created_at < date + timedelta(days=1)
+            Notification.created_at >= start_date,
+            Notification.created_at < end_date,
         ).distinct()
     }

tests/app/dao/notification_dao/test_notification_dao.py

@@ -1,5 +1,5 @@
 import uuid
-from datetime import datetime, timedelta
+from datetime import date, datetime, timedelta
 from functools import partial
 
 import pytest
@@ -24,6 +24,7 @@ from app.dao.notifications_dao import (
     get_notification_with_personalisation,
     get_notifications_for_job,
     get_notifications_for_service,
+    get_service_ids_with_notifications_on_date,
     is_delivery_slow_for_providers,
     notifications_not_yet_sent,
     update_notification_status_by_id,
@@ -41,6 +42,7 @@ from app.models import (
     NOTIFICATION_STATUS_TYPES,
     NOTIFICATION_STATUS_TYPES_FAILED,
     NOTIFICATION_TEMPORARY_FAILURE,
+    SMS_TYPE,
     Job,
     Notification,
     NotificationHistory,
@@ -1721,3 +1723,22 @@ def test_dao_get_letters_and_sheets_volume_by_postage(notify_db_session):
 
     for result in results:
         assert result._asdict() in expected_results
+
+
+@pytest.mark.parametrize('created_at_utc,date_to_check,expected_count', [
+    # Clocks change on the 27th of March 2022, so the query needs to look at the
+    # time range 00:00 - 23:00 (UTC) thereafter.
+    ('2022-03-27T00:30', date(2022, 3, 27), 1),  # 27/03 00:30 GMT
+    ('2022-03-27T22:30', date(2022, 3, 27), 1),  # 27/03 23:30 BST
+    ('2022-03-27T23:30', date(2022, 3, 27), 0),  # 28/03 00:30 BST
+    ('2022-03-26T23:30', date(2022, 3, 26), 1),  # 26/03 23:30 GMT
+])
+def test_get_service_ids_with_notifications_on_date_respects_gmt_bst(
+    sample_template,
+    created_at_utc,
+    date_to_check,
+    expected_count
+):
+    create_notification(template=sample_template, created_at=created_at_utc)
+    service_ids = get_service_ids_with_notifications_on_date(SMS_TYPE, date_to_check)
+    assert len(service_ids) == expected_count