public function platform()
    {
        if (preg_match('/linux/i', $this->server['HTTP_USER_AGENT'])) {
            return 'linux';
        } elseif (preg_match('/macintosh|mac os x/i', $this->server['HTTP_USER_AGENT'])) {
            return 'mac';
        } elseif (preg_match('/windows|win32/i', $this->server['HTTP_USER_AGENT'])) {
            return 'windows';
        }
        return 'unknown';
    }