1 files changed, 49 insertions, 0 deletions
diff --git a/isin/isin.go b/isin/isin.go
new file mode 100644
index 0000000..0117506
--- /dev/null
+++ b/isin/isin.go
@@ -0,0 +1,49 @@
+package isin
+
+import (
+	"strconv"
+	"strings"
+
+	"github.com/neonxp/checksum"
+)
+
+// Check ISIN code
+func Check(number string) error {
+	sum := 0
+	numbersString := ""
+	for _, ch := range strings.ToLower(number) {
+		if int(ch) >= 'a' && int(ch) <= 'z' {
+			numbersString = numbersString + strconv.Itoa(int(ch-'a'+10))
+			continue
+		}
+		numbersString = numbersString + string(ch)
+	}
+	numbers := strings.Split(numbersString, "")
+	l := len(numbers)
+	for i := l; i > 0; i-- {
+		ch := numbers[i-1]
+		num, err := strconv.Atoi(string(ch))
+		if err != nil {
+			return checksum.ErrInvalidNumber
+		}
+		if (l-i)%2 != 0 {
+			n := num * 2
+			if n > 9 {
+				sum += n - 9
+			} else {
+				sum += n
+			}
+		} else {
+			sum += num
+		}
+	}
+	if sum%10 != 0 {
+		return checksum.ErrInvalidChecksum
+	}
+	return nil
+}
+
+func Generate(number string) (string, error) {
+	// TODO implement
+	return "", checksum.ErrNotImplemented
+}