active-svelte/demos/dating/server/realtime.mjs

/**
 * Realtime distributor for the dating server. Holds an in-memory map
 * of `userId -> Set<WebSocket>` so handlers can broadcast events to
 * specific users without each handler caring about transport details.
 *
 * Single-process only: this hub does NOT persist subscriptions or
 * coordinate across instances. Sufficient for the local demo; a
 * production deployment would replace this with Redis pub/sub or
 * similar.
 */

const sockets = new Map(); // userId -> Set<WebSocket>

export function attach(userId, socket) {
	if (!userId || !socket) return () => {};
	let set = sockets.get(userId);
	if (!set) {
		set = new Set();
		sockets.set(userId, set);
	}
	set.add(socket);

	const detach = () => {
		const current = sockets.get(userId);
		if (!current) return;
		current.delete(socket);
		if (current.size === 0) sockets.delete(userId);
	};
	socket.on('close', detach);
	socket.on('error', detach);
	return detach;
}

/**
 * Send `event` to every socket subscribed by any of `userIds`. Each
 * `event` is a plain object that gets JSON-encoded once for all
 * recipients.
 *
 * Failures on individual sockets are swallowed: the close/error
 * handlers attached in `attach` clean them up later, and a single bad
 * socket must never block the rest of the broadcast.
 */
export function broadcast(userIds, event) {
	if (!Array.isArray(userIds) || userIds.length === 0) return;
	const payload = JSON.stringify(event);
	const seen = new Set();
	for (const userId of userIds) {
		if (!userId || seen.has(userId)) continue;
		seen.add(userId);
		const set = sockets.get(userId);
		if (!set || set.size === 0) continue;
		for (const socket of set) {
			try {
				if (socket.readyState === socket.OPEN) socket.send(payload);
			} catch {
				// best-effort
			}
		}
	}
}

export function snapshot() {
	const result = {};
	for (const [userId, set] of sockets) result[userId] = set.size;
	return result;
}