[Possibly still in-progress, but it currently 100% works]

Firestore with Firebase User Presence

Working files that leverage Google Cloud Functions to connect a Firestore user collection to a separate Firebase data structure, to make use of Firebase's onDisconnect class.

You'll have to fill in the src/firebase.js config with your own information.

Google Cloud DB architecture:

Firestore:

• Collection name: users
• Document: [id of user]
• Field: status: { state: "offline"}

Firebase (Real Time Database):

status --> [id of user] --> last_changed: [server timestamp value], state: "offline"

From the Google Firestore docs:

Cloud Firestore doesn't natively support presence, but you can leverage other Firebase products to build a presence system.

Solution: Cloud Functions with Realtime Database

To connect Cloud Firestore to Firebase Realtime Database's native presence feature, use Cloud Functions.

Use Realtime Database to report connection status, then use Cloud Functions to mirror that data into Cloud Firestore.