base62.go

/*
 * MIT License
 *
 * Copyright (c) 2022 cloud-org Authors
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package tools

// see https://codeberg.org/ac/base62/src/branch/main/base62.go
import (
	"errors"
	"math"
	"strings"
)

const Base = 62

// CharacterSet consists of 62 characters [0-9][A-Z][a-z].
const CharacterSet = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"

type Base62 struct {
}

// Encode returns a base62 representation as
// string of the given integer number.
func (*Base62) Encode(num uint32) string {
	b := make([]byte, 0)

	// loop as long the num is bigger than zero
	for num > 0 {
		// receive the rest
		r := math.Mod(float64(num), float64(Base))

		// devide by Base
		num /= Base

		// append chars
		b = append([]byte{CharacterSet[int(r)]}, b...)
	}

	return string(b)
}

// Decode returns a integer number of a base62 encoded string.
func (*Base62) Decode(s string) (uint32, error) {
	var r, pow int

	// loop through the input
	for i, v := range s {
		// convert position to power
		pow = len(s) - (i + 1)

		// IndexRune returns -1 if v is not part of CharacterSet.
		pos := strings.IndexRune(CharacterSet, v)

		if pos == -1 {
			return 0, errors.New("invalid character: " + string(v))
		}

		// calculate
		r += pos * int(math.Pow(float64(Base), float64(pow)))
	}

	return uint32(r), nil
}