public function getAssetDirectory()
    {
        $mergedFileDirectory = StaticContainer::get('path.tmp') . '/assets';

        if (!is_dir($mergedFileDirectory)) {
            Filesystem::mkdir($mergedFileDirectory);
        }

        if (!is_writable($mergedFileDirectory)) {
            throw new Exception("Directory " . $mergedFileDirectory . " has to be writable.");
        }

        return $mergedFileDirectory;
    }