move into separate package

base62/base62.go

@@ -0,0 +1,59 @@
+package base62
+
+import (
+	"fmt"
+	"math"
+	"strings"
+)
+
+const (
+	alphabet = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+	base     = uint32(len(alphabet))
+)
+
+// Encode encodes a uint32 value to a base62 string.
+func Encode(num uint32) string {
+	if num == 0 {
+		return string(alphabet[0])
+	}
+
+	var encoded strings.Builder
+	remainder := uint32(0)
+
+	for num > 0 {
+		remainder = num % base
+		encoded.WriteByte(alphabet[remainder])
+		num /= base
+	}
+
+	// Reverse the encoded string
+	encodedString := encoded.String()
+	reversed := reverse(encodedString)
+	return reversed
+}
+
+// Decode decodes a base62 string to a uint32 value.
+func Decode(encoded string) (uint32, error) {
+	var decoded uint32
+	strLen := len(encoded)
+
+	for i, char := range encoded {
+		index := strings.IndexRune(alphabet, char)
+		if index < 0 {
+			return 0, fmt.Errorf("invalid character: %c", char)
+		}
+
+		decoded += uint32(index) * uint32(math.Pow(float64(base), float64(strLen-i-1)))
+	}
+
+	return decoded, nil
+}
+
+// Reverse a string.
+func reverse(s string) string {
+	runes := []rune(s)
+	for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
+		runes[i], runes[j] = runes[j], runes[i]
+	}
+	return string(runes)
+}