package luhn

import (
    "unicode"
    "strings"
)


// Valid checks a given number for validity according to Luhn's formula
func Valid(card string) bool {
	sum := 0
    card = strings.ReplaceAll(card, " ", "")
    if len(card) <= 1 {
        return false
    }
	for idx, char := range card {
        if !unicode.IsDigit(char) {
            return false
        }
        digit := int(char - '0')
		if (len(card)-idx-1)%2 == 0 {
			sum += digit
		} else {
			digit *= 2
			if digit > 9 {
				sum += digit - 9 
			} else {
				sum += digit
			}
		}
	}
	return sum%10 == 0
}