package main

/**
CREATE TABLE `short_url_map` (
  `id` int(11) unsigned NOT NULL AUTO_INCREMENT,
  `lurl` varchar(160) DEFAULT NULL COMMENT '长地址',
  `surl` varchar(10) DEFAULT NULL COMMENT '短地址',
  `gmt_create` int(11) DEFAULT NULL COMMENT '创建时间',
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8;
*/

import (
    "github.com/spaolacci/murmur3"
    "fmt"
    "math"
    "bytes"
)

// characters used for conversion
const alphabet = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"

// converts number to base62
func Encode(number int) string {
  if number == 0 {
    return string(alphabet[0])
  }

  chars := make([]byte, 0)

  length := len(alphabet)

  for number > 0 {
    result    := number / length
    remainder := number % length
    chars   = append(chars, alphabet[remainder])
    number  = result
  }

  for i, j := 0, len(chars) - 1; i < j; i, j = i + 1, j - 1 {
    chars[i], chars[j] = chars[j], chars[i]
  }

  return string(chars)
}

// converts base62 token to int
func Decode(token string) int {
  number := 0
  idx    := 0.0
  chars  := []byte(alphabet)

  charsLength := float64(len(chars))
  tokenLength := float64(len(token))

  for _, c := range []byte(token) {
    power := tokenLength - (idx + 1)
    index := bytes.IndexByte(chars, c)
    number += index * int(math.Pow(charsLength, power))
    idx++
  }

  return number
}


func main() {
    incr := murmur3.Sum32([]byte("https://u.geekbang.org/subject/python/100038901?utm_source=wechat&utm_medium=pyq02282300&utm_term=wechatpyq02282300"))
    fmt.Println(incr)
    fmt.Println(Encode(int(incr)))
}