Rocket.Chat/app/lib/server/functions/getRoomsWithSingleOwner.js

import { subscriptionHasRole } from '../../../authorization/server';
import { Users, Subscriptions } from '../../../models/server';

export function shouldRemoveOrChangeOwner(subscribedRooms) {
	return subscribedRooms
		.some(({ shouldBeRemoved, shouldChangeOwner }) => shouldBeRemoved || shouldChangeOwner);
}

export function getSubscribedRoomsForUserWithDetails(userId) {
	const subscribedRooms = [];

	// Iterate through all the rooms the user is subscribed to, to check if he is the last owner of any of them.
	Subscriptions.findByUserIdExceptType(userId, 'd').forEach((subscription) => {
		const roomData = {
			rid: subscription.rid,
			t: subscription.t,
			shouldBeRemoved: false,
			shouldChangeOwner: false,
			newOwner: null,
		};

		if (subscriptionHasRole(subscription, 'owner')) {
			// Fetch the number of owners
			const numOwners = Subscriptions.findByRoomIdAndRoles(subscription.rid, ['owner']).count();

			// If it's only one, then this user is the only owner.
			if (numOwners === 1) {
				// Let's check how many subscribers the room has.
				const options = { fields: { 'u._id': 1 }, sort: { ts: 1 } };
				const subscribersCursor = Subscriptions.findByRoomId(subscription.rid, options);

				subscribersCursor.forEach(({ u: { _id: uid } }) => {
					// If we already changed the owner or this subscription is for the user we are removing, then don't try to give it ownership
					if (roomData.shouldChangeOwner || uid === userId) {
						return;
					}
					const newOwner = Users.findOneActiveById(uid, { fields: { _id: 1 } });
					if (!newOwner) {
						return;
					}

					roomData.newOwner = uid;
					roomData.shouldChangeOwner = true;
				});

				// If there's no subscriber available to be the new owner and it's not a public room, we can remove it.
				if (!roomData.shouldChangeOwner && roomData.t !== 'c') {
					roomData.shouldBeRemoved = true;
				}
			}
		} else if (roomData.t !== 'c') {
			// If the user is not an owner, remove the room if the user is the only subscriber
			roomData.shouldBeRemoved = Subscriptions.findByRoomId(roomData.rid).count() === 1;
		}

		subscribedRooms.push(roomData);
	});

	return subscribedRooms;
}