Rocket.Chat/packages/rocketchat-lib/server/functions/getRoomByNameOrIdWithOptionToJoin.js

import { Meteor } from 'meteor/meteor';
import _ from 'underscore';

RocketChat.getRoomByNameOrIdWithOptionToJoin = function _getRoomByNameOrIdWithOptionToJoin({ currentUserId, nameOrId, type = '', tryDirectByUserIdOnly = false, joinChannel = true, errorOnEmpty = true }) {
	let room;

	// If the nameOrId starts with #, then let's try to find a channel or group
	if (nameOrId.startsWith('#')) {
		nameOrId = nameOrId.substring(1);
		room = RocketChat.models.Rooms.findOneByIdOrName(nameOrId);
	} else if (nameOrId.startsWith('@') || type === 'd') {
		// If the nameOrId starts with @ OR type is 'd', then let's try just a direct message
		nameOrId = nameOrId.replace('@', '');

		let roomUser;
		if (tryDirectByUserIdOnly) {
			roomUser = RocketChat.models.Users.findOneById(nameOrId);
		} else {
			roomUser = RocketChat.models.Users.findOne({
				$or: [{ _id: nameOrId }, { username: nameOrId }],
			});
		}

		const rid = _.isObject(roomUser) ? [currentUserId, roomUser._id].sort().join('') : nameOrId;
		room = RocketChat.models.Rooms.findOneById(rid);

		// If the room hasn't been found yet, let's try some more
		if (!_.isObject(room)) {
			// If the roomUser wasn't found, then there's no destination to point towards
			// so return out based upon errorOnEmpty
			if (!_.isObject(roomUser)) {
				if (errorOnEmpty) {
					throw new Meteor.Error('invalid-channel');
				} else {
					return;
				}
			}

			room = Meteor.runAsUser(currentUserId, function() {
				const { rid } = Meteor.call('createDirectMessage', roomUser.username);
				return RocketChat.models.Rooms.findOneById(rid);
			});
		}
	} else {
		// Otherwise, we'll treat this as a channel or group.
		room = RocketChat.models.Rooms.findOneByIdOrName(nameOrId);
	}

	// If no room was found, handle the room return based upon errorOnEmpty
	if (!room && errorOnEmpty) {
		throw new Meteor.Error('invalid-channel');
	} else if (!room) {
		return;
	}

	// If a room was found and they provided a type to search, then check
	// and if the type found isn't what we're looking for then handle
	// the return based upon errorOnEmpty
	if (type && room.t !== type) {
		if (errorOnEmpty) {
			throw new Meteor.Error('invalid-channel');
		} else {
			return;
		}
	}

	// If the room type is channel and joinChannel has been passed, try to join them
	// if they can't join the room, this will error out!
	if (room.t === 'c' && joinChannel) {
		const sub = RocketChat.models.Subscriptions.findOneByRoomIdAndUserId(room._id, currentUserId);

		if (!sub) {
			Meteor.runAsUser(currentUserId, function() {
				return Meteor.call('joinRoom', room._id);
			});
		}
	}

	return room;
};