From c223e2f0fa701a4a85a66d749da02d522f5cf728 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mike=20Schw=C3=B6rer?= <pubgit@mikescher.com>
Date: Thu, 27 Oct 2022 17:55:27 +0200
Subject: [PATCH] added base62

---
 langext/base62.go | 74 +++++++++++++++++++++++++++++++++++++++++++++++
 langext/rand.go   | 23 ---------------
 2 files changed, 74 insertions(+), 23 deletions(-)
 create mode 100644 langext/base62.go

diff --git a/langext/base62.go b/langext/base62.go
new file mode 100644
index 0000000..811de81
--- /dev/null
+++ b/langext/base62.go
@@ -0,0 +1,74 @@
+package langext
+
+import (
+	"crypto/rand"
+	"errors"
+	"math"
+	"math/big"
+	"strings"
+)
+
+var (
+	base62Base         = uint64(62)
+	base62CharacterSet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+)
+
+func RandBase62(rlen int) string {
+	bi52 := big.NewInt(int64(len(base62CharacterSet)))
+
+	randMax := big.NewInt(math.MaxInt64)
+
+	r := ""
+
+	for i := 0; i < rlen; i++ {
+		v, err := rand.Int(rand.Reader, randMax)
+		if err != nil {
+			panic(err)
+		}
+
+		r += string(base62CharacterSet[v.Mod(v, bi52).Int64()])
+	}
+
+	return r
+}
+
+func EncodeBase62(num uint64) string {
+	if num == 0 {
+		return "0"
+	}
+
+	b := make([]byte, 0)
+
+	// loop as long the num is bigger than zero
+	for num > 0 {
+		r := num % base62Base
+
+		num -= r
+		num /= base62Base
+
+		b = append([]byte{base62CharacterSet[int(r)]}, b...)
+	}
+
+	return string(b)
+}
+
+func DecodeBase62(str string) (uint64, error) {
+	if str == "" {
+		return 0, errors.New("empty string")
+	}
+
+	result := uint64(0)
+
+	for _, v := range str {
+		result *= base62Base
+
+		pos := strings.IndexRune(base62CharacterSet, v)
+		if pos == -1 {
+			return 0, errors.New("invalid character: " + string(v))
+		}
+
+		result += uint64(pos)
+	}
+
+	return result, nil
+}
diff --git a/langext/rand.go b/langext/rand.go
index f934abe..9c841cf 100644
--- a/langext/rand.go
+++ b/langext/rand.go
@@ -3,8 +3,6 @@ package langext
 import (
 	"crypto/rand"
 	"io"
-	"math"
-	"math/big"
 )
 
 func RandBytes(size int) []byte {
@@ -15,24 +13,3 @@ func RandBytes(size int) []byte {
 	}
 	return b
 }
-
-func RandBase62(rlen int) string {
-	ecs := "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
-
-	bi52 := big.NewInt(int64(len(ecs)))
-
-	randMax := big.NewInt(math.MaxInt64)
-
-	r := ""
-
-	for i := 0; i < rlen; i++ {
-		v, err := rand.Int(rand.Reader, randMax)
-		if err != nil {
-			panic(err)
-		}
-
-		r += string(ecs[v.Mod(v, bi52).Int64()])
-	}
-
-	return r
-}