RocketChat/Rocket.Chat

import type { IRoom } from '@rocket.chat/core-typings';
import { Rooms } from '@rocket.chat/models';

export async function getDefaultChannels(): Promise<IRoom[]> {
    const defaultRooms = await Rooms.findByDefaultAndTypes(true, ['c', 'p'], {
        projection: { usernames: 0 },
    }).toArray();
    const roomsThatAreGoingToBeJoined = new Set(defaultRooms.map((room) => room._id));

    // If any of those are teams, we need to get all the channels that have the auto-join flag as well
    const teamRooms = defaultRooms.filter((room) => room.teamMain && room.teamId);
    if (teamRooms.length > 0) {
        for await (const teamRoom of teamRooms) {
            const defaultTeamRooms = await Rooms.findDefaultRoomsForTeam(teamRoom.teamId).toArray();

            const defaultTeamRoomsThatWereNotAlreadyAdded = defaultTeamRooms.filter((channel) => !roomsThatAreGoingToBeJoined.has(channel._id));

            defaultTeamRoomsThatWereNotAlreadyAdded.forEach((channel) => roomsThatAreGoingToBeJoined.add(channel._id));
            // Add the channels to the defaultRooms list
            defaultRooms.push(...defaultTeamRoomsThatWereNotAlreadyAdded);
        }
    }

    return defaultRooms;
}