package str

import (
	"math"
	"strings"
)

var Bit62Chars string = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"

// 翻转[]byte
func ByteReverse(a []byte) {
	for left, right := 0, len(a)-1; left < right; left, right = left+1, right-1 {
		a[left], a[right] = a[right], a[left]
	}
}

// int64 -> string
func (s *Str) Bit62Encode(num int64) string {
	bytes := []byte{}
	for num > 0 {
		bytes = append(bytes, Bit62Chars[num%62])
		num = num / 62
	}
	ByteReverse(bytes)
	return string(bytes)
}

// string -> int64
func (s *Str) Bit62Decode(str string) int64 {
	var num int64
	n := len(str)
	for i := 0; i < n; i++ {
		pos := strings.IndexByte(Bit62Chars, str[i])
		num += int64(math.Pow(62, float64(n-i-1)) * float64(pos))
	}
	return num
}

func (s *Str) Bit62Add(base, value string) string {
	return s.Bit62Encode(s.Bit62Decode(base) + s.Bit62Decode(value))
}