SOLID for Firebase Apps

The default Firebase tutorial puts every read, write, and rule check directly in a screen component. That works until your second screen needs the same query, or until you want to test a payment flow without spending real money. This skill is what to do then — applied specifically to Firebase + React Native (the web SDK story is similar).

Minimum viable example

// lib/services/todos.ts — owns Firestore for one collection. SRP.
import firestore from "@react-native-firebase/firestore";