Keep last seen sensor available after first value

custom_components/opendisplay/sensor.py

@@ -141,6 +141,20 @@ def native_value(self) -> float | int | str | datetime | None:
 class OpenDisplayLastSeenSensor(OpenDisplaySensorEntity):
     """last_seen sourced from the bluetooth stack, not the gated callback."""
 
+    def __init__(
+        self,
+        coordinator,
+        description: OpenDisplaySensorEntityDescription,
+    ) -> None:
+        """Initialize the last_seen sensor."""
+        super().__init__(coordinator, description)
+        self._last_seen: datetime | None = None
+
+    @property
+    def available(self) -> bool:
+        """Stay available once a last_seen value has been observed."""
+        return self._last_seen is not None or super().available
+
     @property
     def native_value(self) -> datetime | None:
         # connectable=False matches the Bluetooth advertisement monitor's
@@ -150,8 +164,9 @@ def native_value(self) -> datetime | None:
             self.hass, self.coordinator.address, connectable=False
         )
         if info is None:
-            return None
+            return self._last_seen
         # info.time is a monotonic clock (monotonic_time_coarse); convert to
         # wall time with the same offset the advertisement monitor uses.
         wall = info.time + (time.time() - time.monotonic())
-        return datetime.fromtimestamp(wall, tz=timezone.utc)
+        self._last_seen = datetime.fromtimestamp(wall, tz=timezone.utc)
+        return self._last_seen

tests/test_last_seen.py

@@ -59,6 +59,35 @@ def test_native_value_none_when_no_service_info():
         assert entity.native_value is None
 
 
+def test_last_seen_available_after_first_value_when_coordinator_unavailable():
+    entity = _make_sensor()
+    entity.coordinator.available = False
+    mono = time.monotonic()
+
+    with patch.object(
+        sensor_mod,
+        "async_last_service_info",
+        return_value=SimpleNamespace(time=mono),
+    ):
+        value = entity.native_value
+
+    assert value is not None
+    assert entity.available is True
+
+    with patch.object(sensor_mod, "async_last_service_info", return_value=None):
+        assert entity.native_value == value
+    assert entity.available is True
+
+
+def test_last_seen_unavailable_before_first_value_when_coordinator_unavailable():
+    entity = _make_sensor()
+    entity.coordinator.available = False
+
+    with patch.object(sensor_mod, "async_last_service_info", return_value=None):
+        assert entity.native_value is None
+    assert entity.available is False
+
+
 if __name__ == "__main__":
     import pytest