atomWithCollection.ts

import {
  CollectionReference,
  doc,
  onSnapshot,
  setDoc,
} from "firebase/firestore";
import { WritableAtom, atom } from "jotai";

function atomWithCollection<T>(
  collection: CollectionReference<T>,
): WritableAtom<T[], [string, T], void> {
  const dataAtom = atom<T[]>([]);

  dataAtom.onMount = (dispatch) =>
    onSnapshot(collection, (snapshot) => {
      dispatch(snapshot.docs.map((doc) => doc.data() as T));
    });

  return atom(
    (get) => {
      return get(dataAtom);
    },
    (_get, _set, id, data) => {
      setDoc(doc(collection, id), data);
    },
  );
}

export default atomWithCollection;

This uses the firebase v9 SDK