private function buildFilePath($fileName)
    {
        $digest = md5($fileName);

        $path = $this->basePath . '/' . substr($digest, 0, 1) . '/' . substr($digest, 1, 1);

        if (!is_dir($path)) {
            mkdir($path, 0777, true);
        }

        return $path . '/' . $fileName;
    }