next_playlist_item.js

function _next(guild){
    _ensureMongo();

    return new Promise((resolve, reject) => {
        mongo.collection(`guilds`).findAndModify(
            {guildID: guild},
            [[`_id`, `asc`]],
            {
                $pop: {
                    playlist: -1
                }
            },
            {},
            (err, res) => {
                if(err){
                    return reject(err);
                }

                resolve(res[0]);
            }
        );
    });
}