songs.ts

router.post(
    "/:id/favourite",
    asyncHandler(async (req: Request, res: Response) => {
        const db = getDb();
        const collection = db.collection<Song>("song");
        const songId = new ObjectId(req.params.id);

        const song = await collection.findOne({
            _id: new ObjectId(req.params.id),
        });

        // Check if the song exists
        if (song === null) {
            res.status(404).send("Song not found");
            return;
        }

        const favourites = req.user.favourites ?? [];

        // Define the operator on the favourites list
        const operator = favourites.find((id) => id.equals(songId))
            ? "$pull"
            : "$push";

        await db.collection<User>("user").updateOne(
            {
                _id: req.auth.id,
            },
            {
                [operator]: { favourites: songId },
            }
        );

        // Update the user variable in the request
        req.user = await db
            .collection<User>("user")
            .findOne({ _id: req.auth.id });
        res.status(200).json(req.user.favourites);
    })
);