Get persistent_notifications for lovelace from websocket.

[jeradM]

Frontend changes for home-assistant/core#16503

Lovelace will now use websocket connection and events to fetch/update persistent_notifications

[balloob]

This is very expensive. This will now query the websocket backend whenever hass changes, which is A LOT. We should cache the websocket response in a different variable and only update that on the persistent_notifications_updated event.

[jeradM]

Oh yeah, that was a bad idea

[balloob]

Ha, just realized, we should make this a collection ! That way any location can subscribe to it and it will always stay in sync. Example of collection is here

Docs here. Make sure the first argument to createCollection is unique.

[balloob]

Collections will also fetch again after a reconnect.

[balloob]

The return value of a collection is still an unSub function that should be called when the component disconnects.

[jeradM]

👍 Do we need to change the backend so that it sends the updated data with the event?

[balloob]

No, then you need to get granular events like state_changed and only include the changed pieces.

[balloob]

So do something like this in subscribeUpdates:

const fetchNotifications = conn => conn.sendMessagePromise({
  type: 'persistent_notification/get'
});

const subscribeUpdates = (conn, store) =>
  conn.subscribeEvents(
    event => fetchNotifications(conn).then(notif => store.setState(notif, true)),
    'persistent_notifications_updated'
  );

export const subscribeNotifications = (conn, onChange) =>
  createCollection(
    '_ntf',
    fetchNotifications,
    subscribeUpdates,
    conn,
    onChange
  );

[jeradM]

👍 Will do. Later I can add more fine-grained events so we can update the collection without having to fetch the whole set

[balloob]

I honestly think that it would be overkill. It should be such small data sets.

[balloob]

_notifications

[balloob]

Now that it's only 1 domain, it's faster to do === instead of includes

[balloob]

We can merge this once we are no longer needing to do frontend updates for the beta.