public function isAvailable()
    {
        $ok = $this->enabled;

        $now = time();
        if ($ok && !is_null($this->enableFrom)) {
            $ok = $this->enableFrom <= $now;
        }
        if ($ok && !is_null($this->enableUntil)) {
            $ok = $this->enableUntil > $now;
        }

        return $ok;
    }