chore: Fixed data last updated field

Author: BottlecapDave

_docs/entities.md

@@ -21,6 +21,7 @@ The following attributes are available in addition
 | `is_live` | `boolean` | Determines if the bus is being tracked (`true`) or is from the timetable (`false`) |
 | `stop` | `string` | The ATCO code of the bus stop that is being tracked |
 | `buses` | `list` | The collection of known upcoming buses for the stop |
+| `data_last_updated` | `datetime` | The timestamp when the underlying data was last updated |
 
 For each bus in `buses`, you can find the following attributes
 

custom_components/first_bus/sensor.py

@@ -43,6 +43,7 @@ def __init__(self, data):
     self._attributes = {}
     self._state = None
     self._mins_since_last_update = 0
+    self._data_last_updated = None
 
   @property
   def unique_id(self):
@@ -78,12 +79,13 @@ async def async_update(self):
     self._mins_since_last_update = self._mins_since_last_update - 1
 
     # We only want to update every 5 minutes so we don't hammer the service
+    data_last_updated = None
     if self._mins_since_last_update <= 0:
       bus_times = await self._client.async_get_bus_times(self._data[CONFIG_STOP])
       buses = get_buses(bus_times, now())
       self._buses = buses
       self._mins_since_last_update = MINUTES_BETWEEN_UPDATES
-      self._attributes["data_last_updated"] = now()
+      self._data_last_updated = now()
 
     next_bus = get_next_bus(self._buses, self._data[CONFIG_BUSES], now())
     self._attributes = copy.copy(next_bus)
@@ -92,6 +94,9 @@ async def async_update(self):
 
     self._attributes["stop"] = self._data[CONFIG_STOP]
     self._attributes["buses"] = self._buses
+
+    if self._data_last_updated is not None:
+      self._attributes["data_last_updated"] = self._data_last_updated
 
     if next_bus is not None:
       self._state = next_bus["due"]