public function form($publicKey, $sum, $account, $desc, $currency = 'RUB', $locale = 'ru')
    {
        $vitalParams = array(
            'account'  => $account,
            'currency' => $currency,
            'desc'     => $desc,
            'sum'      => $sum
        );

        $this->params = array_merge($this->params, $vitalParams);

        if ($this->secretKey) {
            $this->params['signature'] = $this->getSignature($vitalParams);
        }

        $this->params['locale'] = $locale;

        return self::FORM_URL . $publicKey . '?' . http_build_query($this->params);
    }