LexiBase64.go

package S

import (
	"sync/atomic"
	"time"

	"github.com/kokizzu/rand"
	"golang.org/x/exp/constraints"

	"github.com/kokizzu/gotro/L"
)

type int64orUint64 interface {
	~int64 | ~uint64
}

const i2c_cb63 = `-0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ_abcdefghijklmnopqrstuvwxyz`

const MaxStrLenCB63 = 11

var c2i_cb63 map[rune]int64
var ModCB63 []uint64
var atom int64

func init() {
	c2i_cb63 = map[rune]int64{}
	for i, ch := range i2c_cb63 {
		c2i_cb63[ch] = int64(i)
	}
	ModCB63 = []uint64{0}
	mod := uint64(1)
	for i := 1; i < MaxStrLenCB63; i++ {
		mod *= 64
		ModCB63 = append(ModCB63, mod)
	}
	ModCB63 = append(ModCB63, 9223372036854775808)
	atom = time.Now().UnixNano()
}

// EncodeCB63 convert integer to custom base-63 encoding that lexicographically correct, positive integer only
//
//	0       -
//	1..10   0..9
//	11..36  A..Z
//	37      _
//	38..63  a..z
//	S.EncodeCB63(11,1) // `A`
//	S.EncodeCB63(1,3) // `--0`
func EncodeCB63[T int64orUint64, L constraints.Integer](id T, minLen L) string {
	if minLen < 1 {
		minLen = 1
	}
	str := make([]byte, 0, 12)
	for id > 0 {
		mod := rune(id % 64)
		str = append(str, i2c_cb63[mod])
		id /= 64
	}
	for L(len(str)) < minLen {
		str = append(str, i2c_cb63[0])
	}
	l := len(str)
	for i, j := 0, l-1; i < l/2; i, j = i+1, j-1 {
		str[i], str[j] = str[j], str[i]
	}
	return string(str)
}

// DecodeCB63 convert custom base-63 encoding to int64
//
//	S.DecodeCB63(`--0`) // 1, true
//	S.DecodeCB64(`(*&#$`) // 0, false
func DecodeCB63[T int64orUint64](str string) (T, bool) {
	res := T(0)
	for _, ch := range str {
		res *= 64
		val, ok := c2i_cb63[ch]
		if L.CheckIf(!ok, `Invalid character for CB63: `+string(ch)) {
			return 0, false
		}
		res += T(val)
	}
	return res, true
}

// RandomCB63 random CB63 n-times, the result is n*MaxStrLenCB63 bytes
func RandomCB63[T constraints.Integer](len T) string {
	if len == 1 {
		return EncodeCB63(rand.Uint64(), MaxStrLenCB63)
	}
	res := ``
	for z := T(0); z < len-1; z++ {
		res += EncodeCB63(rand.Uint64(), MaxStrLenCB63)
	}
	now := atomic.AddInt64(&atom, 1)
	res += EncodeCB63(now, MaxStrLenCB63)
	return res
}