func calcCheckNum(code string) rune {
x3 := len(code) == 7
sum := 0
for _, r := range code {
curNum := utils.RuneToInt(r)
if curNum < 0 || curNum > 9 {
return 'B'
}
if x3 {
curNum = curNum * 3
}
x3 = !x3
sum += curNum
}
return utils.IntToRune((10 - (sum % 10)) % 10)
}
// AddCheckSum calculates the correct check-digit and appends it to the given content.
func AddCheckSum(content string) (string, error) {
if content == "" {
return "", errors.New("content is empty")
}
even := len(content)%2 == 1
sum := 0
for _, r := range content {
if _, ok := encodingTable[r]; ok {
value := utils.RuneToInt(r)
if even {
sum += value * 3
} else {
sum += value
}
even = !even
} else {
return "", fmt.Errorf("can not encode \"%s\"", content)
}
}
return content + string(utils.IntToRune(sum%10)), nil
}