sync.ts

1	import { ref, onValue, type Database } from 'firebase/database';
2	import { decryptJson } from '../../core/crypto';
3
4	type ParticipantRecord = {
5	id?: string;
6	encryptedState?: string;
7	encryptedPosition?: string;
8	[key: string]: unknown;
9	};
10
11	type ParticipantState = Record<string, unknown>;
12
13	type SubscribeToParticipantsOptions = {
14	db: Database;
15	roomId: string;
16	roomKey: CryptoKey \| null;
17	onUpdate: (participants: ParticipantState[]) => void;
18	};
19
20	/**
21	* Subscribes to the participants node for a room, decrypting each record
22	* as needed. Calls onUpdate(participants) after every snapshot resolves.
23	*
24	* @param {object} opts
25	* @param {object} opts.db - Firebase Database instance
26	* @param {string} opts.roomId
27	* @param {CryptoKey\|null} opts.roomKey - AES-GCM key, or null for unencrypted rooms
28	* @param {function} opts.onUpdate - (participants: object[]) => void
29	* @returns {{ participants: object[] }} Shared array reference, mutated in place on each update
30	*/
31	export function subscribeToParticipants({ db, roomId, roomKey, onUpdate }: SubscribeToParticipantsOptions): { participants: ParticipantState[] } {
32	const participantsRef = ref(db, `rooms/${roomId}/participants`);
33	const participants: ParticipantState[] = [];
34	let snapshotVersion = 0;
35
36	onValue(participantsRef, async (snapshot) => {
37	const version = ++snapshotVersion;
38
39	const participantsData = snapshot.val();
40	if (participantsData) {
41	const rawParticipants = Object.values(participantsData as Record<string, ParticipantRecord>);
42	const decrypted = await Promise.all(rawParticipants.map(async (p) => {
43	if (p.encryptedState && roomKey) {
44	try {
45	return await decryptJson(roomKey, p.encryptedState);
46	} catch (err) {
47	console.error('Failed to decrypt participant state', p.id, err);
48	return null;
49	}
50	}
51	if (p.encryptedPosition && roomKey) {
52	try {
53	const position = await decryptJson(roomKey, p.encryptedPosition);
54	const { encryptedPosition: _stripped, ...rest } = p;
55	return { ...rest, position };
56	} catch (err) {
57	console.error('Failed to decrypt legacy participant position', p.id, err);
58	return null;
59	}
60	}
61	return p;
62	}));
63	if (version !== snapshotVersion) return;
64	participants.length = 0;
65	participants.push(...decrypted.filter((value): value is ParticipantState => Boolean(value)));
66	} else {
67	if (version !== snapshotVersion) return;
68	participants.length = 0;
69	}
70
71	onUpdate(participants);
72	});
73
74	return { participants };
75	}