Set the state to a string rather than a datetime.

As reported on issue #2, iOS is fussy about the format of timestamp strings.
The correct ISO format is actually returned by the Metlink API, but when
we parse it into a datetime object, Home Assistant later converts it back
using a more human readable format (a space instead of T between date and time).

Although I had a lot of trouble getting timestamps to display correctly
early on, it seems the format from Metlink API is OK to use as-is.

custom_components/metlink/manifest.json

@@ -8,5 +8,5 @@
     "issue_tracker": "https://github.com/make-all/metlink-nz/issues",
     "name": "Metlink Wellington Transport",
     "requirements": ["isodate==0.6.0"],
-    "version": "1.0.1"
+    "version": "1.0.2"
 }

custom_components/metlink/sensor.py

@@ -215,8 +215,9 @@ async def async_update(self):
                 name = f"{departure[ATTR_SERVICE]} {dest}"
                 if num == 1:
                     # First record is the next departure, so use that
-                    # to set the state (departure time) and friendly name
-                    self._state = dt_util.parse_datetime(time)
+                    # to set the state (departure time)
+                    next_departure = dt_util.parse_datetime(time)
+                    self._state = time
                     self._icon = OPERATOR_ICONS.get(
                         departure[ATTR_OPERATOR], DEFAULT_ICON
                     )
@@ -226,7 +227,7 @@ async def async_update(self):
                     # Dynamic polling of the API to get accurate predictions
                     # close to the time, without overloading the server when
                     # there is nothing pending:
-                    when = (self._state - now).total_seconds()
+                    when = (next_departure - now).total_seconds()
                     # Within 3 minutes, poll next call as well
                     if when < 180:
                         self.update_time = now
@@ -238,10 +239,10 @@ async def async_update(self):
                         self.update_time = now + timedelta(minutes=10)
                     # More than an hour away, don't poll until 1 hour before
                     else:
-                        self.update_time = self._state - timedelta(hours=1)
+                        self.update_time = next_departure - timedelta(hours=1)
 
                     _LOGGER.debug(
-                        f"Next departure at {self._state}, blocking updates until {self.update_time}"
+                        f"Next departure at {next_departure}, blocking updates until {self.update_time}"
                     )
                 else:
                     suffix = f"_{num}"