Laravel根据用户id生成四位数唯一邀请码的方法

<?php

namespace App\Services;// 邀请码服务class InviteCodeService{

    protected $key,$num;
    public function __construct()
    {
        $this->key = 'abcdefghjkmnpqrstuvwxyz123456789';
        // 注意这个key里面不能出现数字0  否则当 求模=0 会重复的

        // 多少进制
        $this->num = strlen($this->key);
    }

    // 传递用户id生成唯一邀请码
    public function enCode(int $user_id)
    {

        $code = ''; // 邀请码
        while ($user_id > 0) { // 转进制
            $mod = $user_id % $this->num; // 求模

            $user_id = ($user_id - $mod) / $this->num;
            $code = $this->key[$mod] . $code;
        }

        $code = str_pad($code, 4, '0', STR_PAD_LEFT); // 不足用0补充
        return $code;
    }


    // 邀请码获取用户id  一般都不需要用到
    function deCode($code)
    {

        if (strrpos($code, '0') !== false)
            $code = substr($code, strrpos($code, '0') + 1);
        $len = strlen($code);
        $code = strrev($code);
        $user_id = 0;
        for ($i = 0; $i < $len; $i++)
            $user_id += strpos($this->key, $code[$i]) * pow($this->num, $i);
        return $user_id;
    }}

    use App\Services\InviteCodeService;
    public function register()
    {
        $this->app->singleton('invite_code',InviteCodeService::class);
    }

      $max_num = 200000;

        $codes = [];
        for ($i = 1; $i <= $max_num; $i++)
            $codes[] =  app('invite_code')->enCode($i);

        $i = 1;
        foreach ($codes as $code){
            $userId = app('invite_code')->deCode($code); // 邀请码获取用户id

            if( $userId != $i)
                dd("邀请码解密错误".$i);
            $i++;
        }

        $unique_count =  count(array_unique($codes));
        dd($unique_count);  // 不重复的总数