creditcard.go

// CreditCardRegex is the pattern used to identify a credit card PAN.
var CreditCardRegex = "^(?:4[0-9]{12}(?:[0-9]{3})?|5[1-5][0-9]{14}|6(?:011|5[0-9][0-9])[0-9]{12}|3[47][0-9]{13}|3(?:0[0-5]|[68][0-9])[0-9]{11}|(?:2131|1800|35\\d{3})\\d{11})$"
var rxCreditCard = regexp.MustCompile(CreditCardRegex)
var rxNotNumber = regexp.MustCompile("[^0-9]+")

// IsCreditCard checks if the string is a credit card.
func IsCreditCard(s string) bool {
	sanitized := rxNotNumber.ReplaceAllString(s, "")
	if !rxCreditCard.MatchString(sanitized) {
		return false
	}
	return ValidLuhn(s)
}

// ValidLuhn returns true or false to indicate whether or not the supplied
// string of 2 or more digits passes or fails the Luhn check algorithm.
func ValidLuhn(number string) bool {
	doubles := []int{0, 2, 4, 6, 8, 1, 3, 5, 7, 9}
	matched, err := regexp.MatchString("^[[:digit:]]{2,}$", number)
	if matched == false || err != nil {
		return false
	}

	checkSum := 0
	for i, double := len(number)-1, false; i >= 0; i-- {
		if double {
			checkSum += doubles[int(number[i]-'0')]
		} else {
			checkSum += int(number[i] - '0')
		}
		double = !double
	}
	return checkSum%10 == 0
}

https://gist.github.com/lfaoro/1476e1e14a76fd8fa6bbbf3a164dd0cf#file-creditcard-go-L7
need it to replace all non-number characters instead of just failing
https://gist.github.com/lfaoro/1476e1e14a76fd8fa6bbbf3a164dd0cf#file-creditcard-go-L7
need it to verify the number is a valid credit card
https://gist.github.com/lfaoro/1476e1e14a76fd8fa6bbbf3a164dd0cf#file-creditcard-go-L19
could be avoided as we have the IsCreditCard step doing that already, although if we want the Luhn function to be used standalone for other types of PANs we need it.