Solve monthly overflow as reported in #399

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Ongoing
 
+- PR [400](https://github.com/plugwise/python-plugwise-usb/pull/400): Fix for Issue [#399](https://github.com/plugwise/python-plugwise-usb/issues/399)
 - Test/validate for Python 3.14
 
 ## v0.47.1 - 2025-09-27

plugwise_usb/nodes/circle.py

@@ -880,9 +880,9 @@ async def clock_synchronize(self) -> bool:
             return False
 
         dt_now = datetime.now(tz=UTC)
-        days_diff = (response.day_of_week.value - dt_now.weekday()) % 7
-        circle_timestamp: datetime = dt_now.replace(
-            day=dt_now.day + days_diff,
+        days_diff = response.day_of_week.value - dt_now.weekday()
+        target_date = dt_now + timedelta(days=days_diff)
+        circle_timestamp = target_date.replace(
             hour=response.time.value.hour,
             minute=response.time.value.minute,
             second=response.time.value.second,

tests/stick_test_data.py

@@ -609,6 +609,11 @@
         b"000000C1",  # Success ack
         b"0000" + b"00D7" + b"0098765432101234",  # msg_id, clock_ack, mac
     ),
+    b"\x05\x05\x03\x0300280098765432101234003010053101261F3D\r\n": (
+        "Circle+ Realtime set clock at month-end for 0098765432101234",
+        b"000000C1",  # Success ack
+        b"0000" + b"00D7" + b"0098765432101234",  # msg_id, clock_ack, mac
+    ),
     b"\x05\x05\x03\x03003E11111111111111111B8A\r\n": (
         "clock for 0011111111111111",
         b"000000C1",  # Success ack

tests/test_usb.py

@@ -3039,3 +3039,58 @@ def fake_cache_bool(dummy: object, setting: str) -> bool | None:
         with patch("aiofiles.threadpool.sync_open", return_value=mock_file_stream):
             await stick.disconnect()
         await asyncio.sleep(1)
+
+    @freeze_time("2026-01-31 10:30:00", real_asyncio=True)
+    @pytest.mark.asyncio
+    async def test_clock_synchronize_month_overflow(
+        self, monkeypatch: pytest.MonkeyPatch
+    ) -> None:
+        """Test clock_synchronize handles month-end date rollover correctly.
+
+        Regression test for issue `#399`: ensures that when the Circle's day_of_week
+        differs from the current weekday near month-end, the date calculation
+        doesn't attempt an invalid day value (e.g., Jan 32).
+        """
+        mock_serial = MockSerial(None)
+        monkeypatch.setattr(
+            pw_connection_manager,
+            "create_serial_connection",
+            mock_serial.mock_connection,
+        )
+        monkeypatch.setattr(pw_sender, "STICK_TIME_OUT", 0.2)
+        monkeypatch.setattr(pw_requests, "NODE_TIME_OUT", 2.0)
+
+        stick = pw_stick.Stick("test_port", cache_enabled=False)
+        await stick.connect()
+        await stick.initialize()
+        await stick.discover_nodes(load=False)
+        await self._wait_for_scan(stick)
+
+        # Get a Circle node
+        circle_node = stick.nodes.get("0098765432101234")
+        assert circle_node is not None
+        await circle_node.load()
+
+        # Mock CircleClockGetRequest.send() to return a response where
+        # day_of_week is Sunday (6) while frozen time is Saturday (5), Jan 31
+        def mock_clock_get_send(self):
+            response = pw_responses.CircleClockResponse()
+            response.timestamp = dt.now(tz=UTC)
+            # Set day_of_week to Sunday (6), requiring +1 day from Saturday Jan 31
+            # Old code: Jan 31 + 1 = day 32 (ValueError)
+            # New code: Jan 31 + timedelta(days=1) = Feb 1 (correct)
+            response.day_of_week.value = 6  # Sunday
+            response.time.value = dt.now(tz=UTC).time()
+            return response
+
+        monkeypatch.setattr(
+            pw_requests.CircleClockGetRequest,
+            "send",
+            mock_clock_get_send,
+        )
+
+        # This should not raise ValueError about invalid day
+        result = await circle_node.clock_synchronize()
+        assert result is True
+
+        await stick.disconnect()