public function countryCode(array $values)
    {
        $existing = array_filter($values, function ($code) {
            $country = $this->country->get($code);
            return isset($country['code']);
        });

        if (count($values) != count($existing)) {
            return $this->translation->text('@name is unavailable', array(
                '@name' => $this->translation->text('Country')));
        }

        return true;
    }