Rocket.Chat/apps/meteor/client/lib/utils/getUidDirectMessage.ts

import type { IRoom, IUser } from '@rocket.chat/core-typings';
import { Meteor } from 'meteor/meteor';

import { ChatRoom } from '../../../app/models/client';

export const getUidDirectMessage = (rid: IRoom['_id'], userId: IUser['_id'] | null = Meteor.userId()): string | undefined => {
	const room = ChatRoom.findOne({ _id: rid }, { fields: { uids: 1 } });

	if (!room?.uids || room.uids.length > 2) {
		return undefined;
	}

	return room.uids.filter((uid) => uid !== userId)[0];
};