cards/validation/validate.go
2025-01-31 21:08:14 +02:00

95 lines
1.6 KiB
Go

package validation
import (
"errors"
"slices"
"strconv"
"strings"
"time"
)
type Card struct {
Pan string
Month string
Year string
}
type ValidationResult struct {
Code int
Error error
}
var ErrValid = ValidationResult{0, errors.New("the card is valid")}
var ErrInvalidPAN = ValidationResult{1, errors.New("invalid PAN")}
var ErrInvalidYear = ValidationResult{2, errors.New("invalid year")}
var ErrInvalidMonth = ValidationResult{3, errors.New("invalid month")}
var ErrExpire = ValidationResult{4, errors.New("expired card")}
func Luhn(pan string) bool {
if pan == "" {
return false
}
lastIndex := len(pan) - 1
asDigits := []int{}
for _, char := range strings.Split(pan, "") {
digit, err := strconv.Atoi(char)
if err != nil {
return false
}
asDigits = append(asDigits, digit)
}
sum := 0
// do we really need reversed iteration?
for i, digit := range slices.Backward(asDigits[:lastIndex]) {
if i%2 == len(pan)%2 {
if digit > 4 {
sum += 2*digit - 9
} else {
sum += 2 * digit
}
} else {
sum += digit
}
}
return asDigits[lastIndex] == (10-(sum%10))%10
}
func Validate(card Card) ValidationResult {
if !Luhn(card.Pan) {
return ErrInvalidPAN
}
year, yearErr := strconv.Atoi(card.Year)
if yearErr != nil || len(card.Year) != 2 {
return ErrInvalidYear
}
month, monthErr := strconv.Atoi(card.Month)
if monthErr != nil || len(card.Month) != 2 || month > 12 || month < 1 {
return ErrInvalidMonth
}
now := time.Now()
// not sure about time zones
cardExpire := time.Date(year+2000, time.Month(month), 1, 0, 0, 0, 0, time.UTC)
if now.After(cardExpire) {
return ErrExpire
}
return ErrValid
}