From 79c590957c640dbcb862352ff7c92872e350138f Mon Sep 17 00:00:00 2001
From: what-00 <what-00@qq.com>
Date: Sat, 15 Apr 2023 00:04:50 +0800
Subject: [PATCH] first commit

---
 README.md      |   1 +
 base62.go      | 121 +++++++++++++++++++++++++++++++++++++++++++++++++
 base62_test.go |  13 ++++++
 go.mod         |   7 +++
 go.sum         |   4 ++
 5 files changed, 146 insertions(+)
 create mode 100644 README.md
 create mode 100644 base62.go
 create mode 100644 base62_test.go
 create mode 100644 go.mod
 create mode 100644 go.sum

diff --git a/README.md b/README.md
new file mode 100644
index 0000000..995862d
--- /dev/null
+++ b/README.md
@@ -0,0 +1 @@
+#go-base62
diff --git a/base62.go b/base62.go
new file mode 100644
index 0000000..ec87997
--- /dev/null
+++ b/base62.go
@@ -0,0 +1,121 @@
+package base62
+
+import (
+	"bytes"
+	"errors"
+
+	"github.com/samber/lo"
+)
+
+type Base62 struct {
+	characters    []byte       // base62 编码规则
+	charactersMap map[byte]int // base62 编码规则
+}
+
+var base62 *Base62
+
+func init() {
+	base62 = &Base62{}
+	base62.SetCharacters([]byte("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"))
+}
+
+func GetInstance() *Base62 {
+	return base62
+}
+
+func (base62 *Base62) SetCharacters(characters []byte) (*Base62, error) {
+	characters = lo.FindUniques(characters)
+	charactersMap := make(map[byte]int)
+
+	if len(characters) != 62 {
+		return nil, errors.New("Invalid characters")
+	}
+
+	for i, v := range characters {
+		charactersMap[v] = i
+	}
+
+	base62.characters = characters
+	base62.charactersMap = charactersMap
+
+	return base62, nil
+}
+
+// Encode function receives a byte slice and encodes it to a string using the alphabet provided
+func (e *Base62) Encode(source []byte) string {
+	if len(source) == 0 {
+		return ""
+	}
+
+	digits := []int{0}
+
+	for i := 0; i < len(source); i++ {
+		carry := int(source[i])
+
+		for j := 0; j < len(digits); j++ {
+			carry += digits[j] << 8
+			digits[j] = carry % 62
+			carry = carry / 62
+		}
+
+		for carry > 0 {
+			digits = append(digits, carry%62)
+			carry = carry / 62
+		}
+	}
+
+	var res bytes.Buffer
+
+	for k := 0; source[k] == 0 && k < len(source)-1; k++ {
+		res.WriteByte(base62.characters[0])
+	}
+
+	for q := len(digits) - 1; q >= 0; q-- {
+		res.WriteByte(base62.characters[digits[q]])
+	}
+
+	return res.String()
+}
+
+// Decode function decodes a string previously obtained from Encode, using the same alphabet and returns a byte slice
+// In case the input is not valid an arror will be returned
+func (base62 *Base62) Decode(source string) ([]byte, error) {
+	if len(source) == 0 {
+		return []byte{}, nil
+	}
+
+	runes := []byte(source)
+
+	bytes := []byte{0}
+	for i := 0; i < len(runes); i++ {
+		value, ok := base62.charactersMap[runes[i]]
+
+		if !ok {
+			return nil, errors.New("Non Base Character")
+		}
+
+		carry := int(value)
+
+		for j := 0; j < len(bytes); j++ {
+			carry += int(bytes[j]) * 62
+			bytes[j] = byte(carry & 0xff)
+			carry >>= 8
+		}
+
+		for carry > 0 {
+			bytes = append(bytes, byte(carry&0xff))
+			carry >>= 8
+		}
+	}
+
+	for k := 0; runes[k] == base62.characters[0] && k < len(runes)-1; k++ {
+		bytes = append(bytes, 0)
+	}
+
+	// Reverse bytes
+	for i, j := 0, len(bytes)-1; i < j; i, j = i+1, j-1 {
+		bytes[i], bytes[j] = bytes[j], bytes[i]
+	}
+
+	return bytes, nil
+}
diff --git a/base62_test.go b/base62_test.go
new file mode 100644
index 0000000..6cc04c3
--- /dev/null
+++ b/base62_test.go
@@ -0,0 +1,13 @@
+package base62
+
+import (
+	"testing"
+)
+
+func TestEncode(t *testing.T) {
+	e := GetInstance().Encode([]byte("问问哇啊啊"))
+	t.Log(e)
+
+	d, err := GetInstance().Decode(e)
+	t.Log(string(d), err)
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..d118a3f
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,7 @@
+module git.fsdpf.net/go/base62
+
+go 1.18
+
+require github.com/samber/lo v1.38.1
+
+require golang.org/x/exp v0.0.0-20220303212507-bbda1eaf7a17 // indirect
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..7a26b7e
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,4 @@
+github.com/samber/lo v1.38.1 h1:j2XEAqXKb09Am4ebOg31SpvzUTTs6EN3VfgeLUhPdXM=
+github.com/samber/lo v1.38.1/go.mod h1:+m/ZKRl6ClXCE2Lgf3MsQlWfh4bn1bz6CXEOxnEXnEA=
+golang.org/x/exp v0.0.0-20220303212507-bbda1eaf7a17 h1:3MTrJm4PyNL9NBqvYDSj3DHl46qQakyfqfWo4jgfaEM=
+golang.org/x/exp v0.0.0-20220303212507-bbda1eaf7a17/go.mod h1:lgLbSvA5ygNOMpwM/9anMpWVlVJ7Z+cHWq/eFuinpGE=