Include last day of month in monthly locale stats (mozilla#3993)

Co-authored-by: Matjaž Horvat <matjaz.horvat@gmail.com>

Author: flodolo

pontoon/messaging/emails.py

@@ -72,14 +72,26 @@ def _get_monthly_locale_actions(months_ago):
 
 def _get_monthly_locale_stats(months_ago):
     month_date = timezone.now() - relativedelta(months=months_ago)
-    last_day = calendar.monthrange(month_date.year, month_date.month)[1]
 
-    snapshots = LocaleInsightsSnapshot.objects.filter(
-        created_at__day=last_day,
-        created_at__month=month_date.month,
-        created_at__year=month_date.year,
+    # collect_insights() takes data snapshots at the beginning of the day,
+    # every day. To represent the state of the past month, we should
+    # use the snapshot from the first day of the current month.
+    next_month = month_date + relativedelta(months=1)
+
+    snapshots = list(
+        LocaleInsightsSnapshot.objects.filter(
+            created_at__day=1,
+            created_at__month=next_month.month,
+            created_at__year=next_month.year,
+        )
     )
 
+    if not snapshots:
+        raise LookupError(
+            f"No LocaleInsightsSnapshot found for "
+            f"{next_month.year}-{next_month.month:02d}-01."
+        )
+
     return {snapshot.locale_id: snapshot for snapshot in snapshots}
 
 
@@ -108,7 +120,7 @@ def _get_monthly_locale_contributors(locales, months_ago):
     }
 
     # Get all contributors in the given month,
-    # grouped by locale and orderd by contribution count
+    # grouped by locale and ordered by contribution count
     monthly_contributors = (
         actions.filter(
             created_at__month=month_date.month,

pontoon/messaging/tests/test_emails.py

@@ -1,10 +1,17 @@
+from datetime import date
 from unittest.mock import patch
 
 import pytest
 
 from django.test.client import RequestFactory
+from django.utils import timezone
 
-from pontoon.messaging.emails import send_verification_email
+from pontoon.insights.models import LocaleInsightsSnapshot
+from pontoon.messaging.emails import (
+    _get_monthly_locale_stats,
+    send_verification_email,
+)
+from pontoon.test.factories import LocaleFactory
 
 
 @pytest.mark.django_db
@@ -21,3 +28,38 @@ def test_send_verification_email(member):
         kwargs = mock_email_message.call_args.kwargs
         assert link in kwargs["body"]
         assert kwargs["to"] == [request.user.email]
+
+
+@pytest.mark.django_db
+def test_get_monthly_locale_stats_uses_end_of_month_snapshot():
+    locale = LocaleFactory(code="x-test", name="Test Language")
+
+    # Simulate 6 strings added on October 30.
+    LocaleInsightsSnapshot.objects.create(
+        locale=locale,
+        created_at=date(2025, 10, 31),
+        total_strings=100,
+        approved_strings=94,
+        completion=94.0,
+    )
+
+    # Nov 1 snapshot is taken at midnight, capturing end of Oct 31.
+    # The 6 strings were translated.
+    snapshot_nov_1 = LocaleInsightsSnapshot.objects.create(
+        locale=locale,
+        created_at=date(2025, 11, 1),
+        total_strings=100,
+        approved_strings=100,
+        completion=100.0,
+    )
+
+    with patch("pontoon.messaging.emails.timezone") as mock_tz:
+        mock_tz.now.return_value = timezone.datetime(
+            2025, 11, 1, 6, 30, 0, tzinfo=timezone.utc
+        )
+        result = _get_monthly_locale_stats(months_ago=1)
+
+    assert locale.pk in result
+    assert result[locale.pk].pk == snapshot_nov_1.pk
+    assert result[locale.pk].approved_strings == 100
+    assert result[locale.pk].completion == 100.0