From 27c16537ec7fcc549273bd378871f7cff1ff05ac Mon Sep 17 00:00:00 2001
From: thinkgos <thinkgo@aliyun.com>
Date: Tue, 3 Dec 2024 23:15:47 +0800
Subject: [PATCH] fixfeat: add base32n

---
 base32n/base32n.go      | 73 +++++++++++++++++++++++++++++++++++++++++
 base32n/base32n_test.go | 22 +++++++++++++
 2 files changed, 95 insertions(+)
 create mode 100644 base32n/base32n.go
 create mode 100644 base32n/base32n_test.go

diff --git a/base32n/base32n.go b/base32n/base32n.go
new file mode 100644
index 0000000..96fa625
--- /dev/null
+++ b/base32n/base32n.go
@@ -0,0 +1,73 @@
+package base32n
+
+import (
+	"errors"
+	"strconv"
+	"unsafe"
+)
+
+var StdEncoding = NewEncoding("abcdefghijklmnopqrstuvwxyz234567")
+
+const (
+	decodeMapInitialize = "" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" +
+		"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff"
+	invalidIndex = '\xff'
+)
+
+type Encoding struct {
+	encode    [32]byte   // mapping of symbol index to symbol byte value
+	decodeMap [256]uint8 // mapping of symbol byte value to symbol index
+}
+
+func NewEncoding(encoder string) *Encoding {
+	e := new(Encoding)
+	copy(e.encode[:], encoder)
+	copy(e.decodeMap[:], decodeMapInitialize)
+	for i := 0; i < len(encoder); i++ {
+		char := encoder[i]
+		e.decodeMap[char] = uint8(i)
+	}
+	return e
+}
+
+func (enc *Encoding) Encode(num int64) string {
+	result := make([]byte, 0, 13)
+	for num > 0 {
+		remainder := num & 0x1f
+		result = append(result, enc.encode[remainder])
+		num >>= 5
+	}
+	for i, j := 0, len(result)-1; i < j; i, j = i+1, j-1 {
+		result[i], result[j] = result[j], result[i]
+	}
+	return unsafe.String(unsafe.SliceData(result), len(result))
+}
+
+func (enc *Encoding) Decode(s string) (int64, error) {
+	var num int64 = 0
+
+	for i := 0; i < len(s); i++ {
+		char := s[i]
+		val := enc.decodeMap[char]
+		if val == invalidIndex {
+			return 0, errors.New("illegal base32n data at input byte " + strconv.FormatInt(int64(char), 10))
+		}
+		num += int64(val) * int64(1<<uint(5*(len(s)-1-i)))
+	}
+	return num, nil
+}
diff --git a/base32n/base32n_test.go b/base32n/base32n_test.go
new file mode 100644
index 0000000..ba909bb
--- /dev/null
+++ b/base32n/base32n_test.go
@@ -0,0 +1,22 @@
+package base32n
+
+import (
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func Test_ValidString(t *testing.T) {
+	want := time.Now().UnixMicro()
+	s := StdEncoding.Encode(want)
+
+	got, err := StdEncoding.Decode(s)
+	require.NoError(t, err)
+	require.Equal(t, want, got)
+}
+
+func Test_IllegalString(t *testing.T) {
+	_, err := StdEncoding.Decode("bril03vgrwtu")
+	require.Error(t, err)
+}