public function key($reset = false)
    {
        static $key;
        $key = $reset ? false : $key;
        if (!$key) {
            $path = $this->path . "/.cache_key";
            if (file_exists($path)) {
                $key = file_get_contents($path);
            } else {
                $key = $this->setKey();
            }
        }
        return $key;
    }