songs.ts

router.get(
    "/recommend",
    asyncHandler(async (req: Request, res: Response) => {
        const db = getDb();
        const collection = db.collection<Song>("song");

        // /songs/recommend?limit=N
        const limit = parseInt(req.params.limit) || 20;

        // Array of song IDs
        const favourites = req.user.favourites;

        let suggestions: ObjectId[];

        if (!favourites) {
            // Getting any songs
            const songs = await collection
                .find({}, { limit, projection: { _id: 1 } })
                .toArray();
            suggestions = songs.map((song) => song._id);
        } else {
            // Suggesting
            const favouriteCluster = await getFavouriteCluster(favourites);
            suggestions = await getSuggestions(favouriteCluster, favourites);
        }

        res.status(200).json(suggestions);
    })
);