public function directories($directoryName)
    {
        if (!$this->isDir($directoryName)) {
            throw new FileNotFoundException('Directory not found in the path [ ' . $directoryName . ' ].');
        }

        $iterator = new RecursiveIteratorIterator(
            new RecursiveDirectoryIterator($directoryName,
                RecursiveDirectoryIterator::CURRENT_AS_FILEINFO)
        );

        $directories = [];

        foreach($iterator as $file) {
            if($file->isDir()) {
                if( !(substr($file,-2) === '..')) {
                    $directories[] = trim($file,'.');
                }
            }
        }

        array_shift($directories);

        return $directories;
    }