initial

cnpj/generate.go

@@ -0,0 +1,88 @@
+package cnpj
+
+import (
+	"fmt"
+	"math/rand"
+	"strings"
+)
+
+var (
+	cnpjP1 = []int{5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2}
+	cnpjP2 = []int{6, 5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2}
+)
+
+const alphaChars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+func Generate() string {
+	return generate(false)
+}
+
+func GenerateAlpha() string {
+	return generate(true)
+}
+
+func generate(alpha bool) string {
+	for {
+		var b strings.Builder
+		b.Grow(14)
+		for range 12 {
+			if alpha {
+				b.WriteByte(alphaChars[rand.Intn(len(alphaChars))])
+			} else {
+				b.WriteByte(byte('0' + rand.Intn(10)))
+			}
+		}
+		s := b.String()
+		if isRepetitive(s) {
+			continue
+		}
+		dv1 := computeDV(s, cnpjP1, alpha)
+		s2 := s + string(byte('0'+dv1))
+		dv2 := computeDV(s2, cnpjP2, alpha)
+		return s + string(byte('0'+dv1)) + string(byte('0'+dv2))
+	}
+}
+
+func computeDV(s string, table []int, alpha bool) int {
+	total := 0
+	for i, w := range table {
+		c := s[i]
+		var val int
+		if alpha {
+			val = alphaValue(rune(c))
+		} else {
+			val = int(c - '0')
+		}
+		total += val * w
+	}
+	r := total % 11
+	if r >= 2 {
+		return 11 - r
+	}
+	return 0
+}
+
+func alphaValue(r rune) int {
+	return int(r) - 48
+}
+
+func isRepetitive(s string) bool {
+	if len(s) == 0 {
+		return false
+	}
+	c := s[0]
+	for i := 1; i < len(s); i++ {
+		if s[i] != c {
+			return false
+		}
+	}
+	return true
+}
+
+func Format(cnpj string) string {
+	if len(cnpj) != 14 {
+		return cnpj
+	}
+	return fmt.Sprintf("%s.%s.%s/%s-%s",
+		cnpj[:2], cnpj[2:5], cnpj[5:8], cnpj[8:12], cnpj[12:])
+}