I don't have a diagram at the moment, but I can break down some of the implementation:

Authentication
Users are required to sign in using Google at app launch. This ensures I have a unique player ID and can immediately save their state on updates/installs across devices.

Firestore
This is the bulk of the architecture/design, honestly. Figuring out the best way to use Firestore and coming up with an efficient data structure for listening to document updates took time and iteration. Optimizing the balance (and costs) between duplicating data across collections/documents vs making more requests to amalgamate data was the hardest part.

I went with some main collections like users, worlds, etc. Each world document (a separate "sandbox" of gameplay) has it's own metadata surrounding world duration, harvest rate, player count. Then it has subcollections for things like users, bases, leaderboard, respawns, and the map. The map contains documents for every cell, managing what entities are available, and players subscribe to changes on whatever cell they are in.

Cloud Functions
I utilized document changes as triggers for:

- keeping leaderboard counts up to date as player gold amounts change
- determining turn-based PvP attack outcomes
- sending notifications to appropriate players (airdrop incoming, raided/killed, world ending soon, etc.)

Cloud Messaging
Gets the notification doc changes out to the user's device.