fix age to start at 0 on start date of cycle instead of 1

backend/apps/farms/tests.py

@@ -128,6 +128,30 @@ class FarmAPITests(TestCase):
         self.assertEqual(Flock.objects.filter(kandang=self.kandang).count(), 1)
         self.assertEqual(flock.kandang_id, self.kandang.pk)
 
+    def test_current_day_is_zero_based_from_start_date(self):
+        start = date(2026, 9, 2)
+        cycle = Cycle.objects.create(
+            kandang=self.kandang,
+            total_days=35,
+            start_date=start,
+            end_date=start + timedelta(days=34),
+            doc_in_weight=40,
+            doc_in_count=9000,
+            status=Cycle.STATUS_ACTIVE,
+        )
+
+        with patch(
+            "apps.operations.services.visibility.visible_through_date",
+            return_value=start,
+        ):
+            self.assertEqual(cycle.current_day, 0)
+
+        with patch(
+            "apps.operations.services.visibility.visible_through_date",
+            return_value=start + timedelta(days=1),
+        ):
+            self.assertEqual(cycle.current_day, 1)
+
     def test_list_flocks_by_kandang(self):
         self.client.force_authenticate(self.user)
         Flock.objects.create(flock_name="Lantai 1", kandang=self.kandang)