protected function parseCurrencyArgument($data)
    {
        if (is_string($data)) {
            $currency = $data;
        } elseif (is_array($data)) {
            if (isset($data['country'])) {
                $currency = CountryToCurrency::getCurrency($data['country']);
            } elseif (isset($data['currency'])) {
                $currency = $data['currency'];
            } else {
                throw new Exception\InvalidArgumentException('Please provide country or currency!');
            }
        } else {
            throw new Exception\InvalidArgumentException('Invalid currency provided. String or array expected.');
        }

        return $currency;
    }