koel/app/Services/PlaylistService.php

<?php

namespace App\Services;

use App\Models\Playlist;
use App\Models\User;

class PlaylistService
{
    public function createPlaylist(string $name, User $user, array $songs, array $ruleGroups): Playlist
    {
        /** @var Playlist $playlist */
        $playlist = $user->playlists()->create([
            'name' => $name,
            'rules' => $ruleGroups,
        ]);

        if (!$playlist->is_smart && $songs) {
            $playlist->songs()->sync($songs);
        }

        return $playlist;
    }
}