Prohibit creating & updating past overrides (#1474)

# What this PR does
Prohibits creating & updating overrides in the past when using the web
UI.

## Which issue(s) this PR fixes
https://github.com/grafana/oncall/issues/1221

## Checklist

- [x] Tests updated
- [x] `CHANGELOG.md` updated

CHANGELOG.md

@@ -5,6 +5,12 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## Unreleased
+
+### Fixed
+
+- Prohibit creating & updating past overrides ([1474](https://github.com/grafana/oncall/pull/1474))
+
 ## v1.1.33 (2023-03-07)
 
 ### Fixed

engine/apps/api/serializers/on_call_shifts.py

@@ -1,3 +1,4 @@
+from django.utils import timezone
 from rest_framework import serializers
 
 from apps.schedules.models import CustomOnCallShift, OnCallScheduleWeb
@@ -93,10 +94,13 @@ class OnCallShiftSerializer(EagerLoadingMixin, serializers.ModelSerializer):
                 result.append(users_dict)
         return result
 
-    def _validate_shift_end(self, start, end):
+    def _validate_shift_end(self, start, end, event_type):
         if end <= start:
             raise serializers.ValidationError({"shift_end": ["Incorrect shift end date"]})
 
+        if event_type == CustomOnCallShift.TYPE_OVERRIDE and timezone.now() > end:
+            raise serializers.ValidationError({"shift_end": ["Cannot create or update an override in the past"]})
+
     def _validate_frequency(self, frequency, event_type, rolling_users, interval, by_day, until):
         if frequency is None:
             if rolling_users and len(rolling_users) > 1:
@@ -157,7 +161,7 @@ class OnCallShiftSerializer(EagerLoadingMixin, serializers.ModelSerializer):
         # convert shift_end into internal value and validate
         raw_shift_end = self.initial_data["shift_end"]
         shift_end = serializers.DateTimeField().to_internal_value(raw_shift_end)
-        self._validate_shift_end(validated_data["start"], shift_end)
+        self._validate_shift_end(validated_data["start"], shift_end, event_type)
 
         validated_data["duration"] = shift_end - validated_data["start"]
         if validated_data.get("schedule"):

engine/apps/api/tests/test_oncall_shift.py

@@ -921,6 +921,30 @@ def test_create_on_call_shift_override_invalid_data(on_call_shift_internal_api_s
     assert response.data["frequency"][0] == "Cannot set 'frequency' for shifts with type 'override'"
 
 
+@pytest.mark.django_db
+def test_create_on_call_shift_override_in_past(on_call_shift_internal_api_setup, make_user_auth_headers):
+    token, user1, _, _, schedule = on_call_shift_internal_api_setup
+    client = APIClient()
+    url = reverse("api-internal:oncall_shifts-list")
+    start_date = timezone.now().replace(microsecond=0, tzinfo=None) - timezone.timedelta(hours=2)
+
+    data = {
+        "title": "Test Shift Override",
+        "type": CustomOnCallShift.TYPE_OVERRIDE,
+        "schedule": schedule.public_primary_key,
+        "priority_level": 0,
+        "shift_start": start_date.strftime("%Y-%m-%dT%H:%M:%SZ"),
+        "shift_end": (start_date + timezone.timedelta(hours=1)).strftime("%Y-%m-%dT%H:%M:%SZ"),
+        "rotation_start": start_date.strftime("%Y-%m-%dT%H:%M:%SZ"),
+        "rolling_users": [[user1.public_primary_key]],
+    }
+
+    response = client.post(url, data, format="json", **make_user_auth_headers(user1, token))
+
+    assert response.status_code == status.HTTP_400_BAD_REQUEST
+    assert response.data["shift_end"][0] == "Cannot create or update an override in the past"
+
+
 @pytest.mark.django_db
 @pytest.mark.parametrize(
     "role,expected_status",