Blog on PassiveBluetoothProcessorCoordinator (#1427)

Co-authored-by: Martin Hjelmare <marhje52@gmail.com>

blog/2022-08-08-bluetooth-api-changes.md

@@ -0,0 +1,45 @@
+---
+author: John Carr
+authorURL: https://github.com/Jc2k
+title: "Bluetooth passive sensor API changes for 2022.9"
+---
+
+For Home Assistant Core 2022.9 we have changed the `PassiveBluetoothProcessorCoordinator` and `PassiveBluetoothDataProcessor` bluetooth API's to make `PassiveBluetoothProcessorCoordinator` responsible for parsing. The coordinator then pushes parsed data to `PassiveBluetoothDataProcessor` instances.
+
+PassiveBluetoothProcessorCoordinator now takes a mandatory update_method callback that receives bluetooth advertisements (in the form of BluetoothServiceInfoBleak) and returns the data that should be handed off to any subscribed PassiveBluetoothDataProcessor:
+
+```python
+def my_parser(service_info: BluetoothServiceInfoBleak) -> MyDataClass:
+    ...
+
+    return MyDataClass(
+        a=some_parsed_data,
+        b=some_other_parsed_data,
+    )
+
+
+coordinator = PassiveBluetoothProcessorCoordinator(
+    hass,
+    _LOGGER,
+    address=address,
+    mode=BluetoothScanningMode.PASSIVE,
+    update_method=my_parser,
+)
+```
+
+PassiveBluetoothDataProcessor still takes an update_method, but instead of a BluetoothServiceInfoBleak, it now receives the data returned from PassiveBluetoothProcessorCoordinator's update_method. It should still return a `PassiveBluetoothDataUpdate` as before:
+
+```python
+def sensor_update_to_bluetooth_data_update(
+    sensor_update: MyDataClass,
+) -> PassiveBluetoothDataUpdate:
+    """Convert a sensor update to a bluetooth data update."""
+    ...
+    return PassiveBluetoothDataUpdate( ... )
+
+processor = PassiveBluetoothDataProcessor(sensor_update_to_bluetooth_data_update)
+```
+
+All the built-in integrations have already been converted, so take a look at them for more examples.
+
+This change will help integrations that need to start parsing data before loading a platform (for example, the list of platforms to load depend on data from the advertisements) or changes where a single advertisement drives multiple platforms (you won't have to parse the broadcast twice).