feat(fallback): add bucket for last night shifts from 20:00 on

shiftregister/fallback/models.py

@@ -1,15 +1,15 @@
 import math
 import secrets
 from base64 import urlsafe_b64encode
+from datetime import datetime, time
 
 from django.db.models import Count, Exists, ExpressionWrapper, Max, OuterRef, Sum
 from django.db.models.fields import DateTimeField
 from django.db.models.lookups import LessThan
+from django.utils import timezone
 
 from shiftregister.importer.models import *
 
-night_shift_query = Q(start_at__hour__gte=21) | Q(start_at__hour__lte=10)
-
 
 def generate_id():
     return int.from_bytes(secrets.token_bytes(3), byteorder="big")
@@ -32,14 +32,32 @@ class TeamMember(models.Model):
         )
 
     def assign_random_shifts(self):
+        needs_fallback = Q(deleted=False, calendar__needs_fallback=True)
+
+        current_tz = timezone.get_current_timezone()
+        # create a datetime combining the last date having fallback shifts
+        # after 20:00 with the time 20:00 in the current timezone
+        last_night = datetime.combine(
+            Event.objects.filter(needs_fallback, start_at__hour__gte=20)
+            .latest("start_at")
+            .start_at.astimezone(current_tz),
+            time(hour=20),
+            current_tz,
+        )
+
+        is_last_night = Q(start_at__gte=last_night)
+        is_night_shift = Q(start_at__hour__gte=21) | Q(start_at__hour__lte=10)
+
         if self.fallback_shifts.count() != 0:
             return
-        selector1 = (~night_shift_query) & Q(
-            deleted=False, calendar__needs_fallback=True
-        )
-        selector2 = night_shift_query & Q(deleted=False, calendar__needs_fallback=True)
-        self._assign_from_bucket(selector1)
-        self._assign_from_bucket(selector2)
+
+        day_shifts = ~is_night_shift & ~is_last_night & needs_fallback
+        night_shifts = is_night_shift & ~is_last_night & needs_fallback
+        shit_shifts = is_last_night & needs_fallback
+
+        self._assign_from_bucket(day_shifts)
+        self._assign_from_bucket(night_shifts)
+        self._assign_from_bucket(shit_shifts)
 
     def _assign_from_bucket(self, bucket_selector):
         free_bucket = (