package card

import "errors"

var (
	ErrCardRequired = errors.New("card number is required")
	ErrCardLength   = errors.New("card number must contain exactly 16 digits")
	ErrCardNumeric  = errors.New("card number must contain only digits")
)

func Validate(number string) error {
	if number == "" {
		return ErrCardRequired
	}

	if len(number) != 16 {
		return ErrCardLength
	}

	for _, char := range number {
		if char < '0' || char > '9' {
			return ErrCardNumeric
		}
	}

	return nil
}

func Mask(number string) string {
	if Validate(number) != nil {
		return ""
	}

	return number[:6] + "******" + number[12:]
}