waterleaksensor: use parent's Time for alert timestamp (#1614)

We do not, by design, add Time module for hub's children.
This has a side-effect that we need to fallback to the parent's time
module to allow presenting the correct timestamp for the last alert.

kasa/smart/modules/waterleaksensor.py

@@ -4,8 +4,10 @@ from __future__ import annotations
 
 from datetime import datetime
 from enum import Enum
+from typing import TYPE_CHECKING
 
 from ...feature import Feature
+from ...interfaces.time import Time
 from ..smartmodule import Module, SmartModule
 
 
@@ -76,6 +78,17 @@ class WaterleakSensor(SmartModule):
         """Return true if alarm is active."""
         return self._device.sys_info["in_alarm"]
 
+    @property
+    def _time_module(self) -> Time:
+        """Return time module from the parent for timestamp calculation."""
+        parent = self._device.parent
+        if TYPE_CHECKING:
+            from ..smartdevice import SmartDevice
+
+            assert isinstance(parent, SmartDevice)
+
+        return parent.modules[Module.Time]
+
     @property
     def alert_timestamp(self) -> datetime | None:
         """Return timestamp of the last leak trigger."""
@@ -84,5 +97,5 @@ class WaterleakSensor(SmartModule):
             return None
 
         ts = self._device.sys_info["trigger_timestamp"]
-        tz = self._device.modules[Module.Time].timezone
+        tz = self._time_module.timezone
         return datetime.fromtimestamp(ts, tz=tz)

tests/smart/modules/test_waterleak.py

@@ -5,6 +5,7 @@ import pytest
 
 from kasa.smart.modules import WaterleakSensor
 
+from ...conftest import get_device_for_fixture_protocol
 from ...device_fixtures import parametrize
 
 waterleak = parametrize(
@@ -12,6 +13,12 @@ waterleak = parametrize(
 )
 
 
+@pytest.fixture
+async def parent(request):
+    """Get a dummy parent for tz tests."""
+    return await get_device_for_fixture_protocol("H100(EU)_1.0_1.5.5.json", "SMART")
+
+
 @waterleak
 @pytest.mark.parametrize(
     ("feature", "prop_name", "type"),
@@ -21,8 +28,9 @@ waterleak = parametrize(
         ("water_leak", "status", Enum),
     ],
 )
-async def test_waterleak_properties(dev, feature, prop_name, type):
+async def test_waterleak_properties(dev, parent, feature, prop_name, type):
     """Test that features are registered and work as expected."""
+    dev._parent = parent
     waterleak: WaterleakSensor = dev.modules["WaterleakSensor"]
 
     prop = getattr(waterleak, prop_name)
@@ -34,8 +42,9 @@ async def test_waterleak_properties(dev, feature, prop_name, type):
 
 
 @waterleak
-async def test_waterleak_features(dev):
+async def test_waterleak_features(dev, parent):
     """Test waterleak features."""
+    dev._parent = parent
     waterleak: WaterleakSensor = dev.modules["WaterleakSensor"]
 
     assert "water_leak" in dev.features
@@ -43,3 +52,6 @@ async def test_waterleak_features(dev):
 
     assert "water_alert" in dev.features
     assert dev.features["water_alert"].value == waterleak.alert
+
+    assert "water_alert_timestamp" in dev.features
+    assert dev.features["water_alert_timestamp"].value == waterleak.alert_timestamp