<?php
// +----------------------------------------------------------------------
// | Bwsaas
// +----------------------------------------------------------------------
// | Copyright (c) 2015~2020 http://www.buwangyun.com All rights reserved.
// +----------------------------------------------------------------------
// | Licensed ( http://www.apache.org/licenses/LICENSE-2.0 )
// +----------------------------------------------------------------------
// | Gitee ( https://gitee.com/buwangyun/bwsaas )
// +----------------------------------------------------------------------
// | Author: buwangyun <hnlg666@163.com>
// +----------------------------------------------------------------------
// | Date: 2020-9-28 10:55:00
// +----------------------------------------------------------------------
/**
 * 加解密类
 */
namespace encrypter;

class Encrypter {

    protected const DEFAULT_KEYS='bw_key';
    /**
     * 加密函数
     * @param string $string 字符串
     * @param string $key 密匙
     * @param int $expiry
     * @return string
     */
    public static function bwEncode($string, $key='',$expiry=0){
        return self::bw_encrypt($string, $key, false,$expiry);
    }

    /**
     * 解密函数
     * @param  string $string 加密字符串
     * @param  string $key    密匙
     * @return mixed
     */
    public static function bwDecode($string,$key=''){
        return self::bw_encrypt($string, $key, true);
    }

    /**
     * 加解密算法，引用discuz中使用的加密解密算法
     * @param $string
     * @param string $key
     * @param false $operation
     * @param int $expiry
     * @return false|string
     */
    protected static function bw_encrypt($string,$key='',$operation=false,$expiry=0){
        $ckey_length = 4;
        $key = md5($key ? $key : self::DEFAULT_KEYS);
        $keya = md5(substr($key, 0, 16));
        $keyb = md5(substr($key, 16, 16));
        $keyc = $ckey_length ? ($operation? substr($string, 0, $ckey_length):substr(md5(microtime()), -$ckey_length)) : '';
        $cryptkey = $keya.md5($keya.$keyc);
        $key_length = strlen($cryptkey);
        $string = $operation? base64_decode(substr($string, $ckey_length)) :
            sprintf('%010d', $expiry ? $expiry + time() : 0).substr(md5($string.$keyb), 0, 16).$string;
        $string_length = strlen($string);
        $result = '';
        $box = range(0, 255);
        $rndkey = array();
        for($i = 0; $i <= 255; $i++) {
            $rndkey[$i] = ord($cryptkey[$i % $key_length]);
        }
        for($j = $i = 0; $i < 256; $i++) {
            $j = ($j + $box[$i] + $rndkey[$i]) % 256;
            $tmp = $box[$i];
            $box[$i] = $box[$j];
            $box[$j] = $tmp;
        }
        for($a = $j = $i = 0; $i < $string_length; $i++) {
            $a = ($a + 1) % 256;
            $j = ($j + $box[$a]) % 256;
            $tmp = $box[$a];
            $box[$a] = $box[$j];
            $box[$j] = $tmp;
            $result .= chr(ord($string[$i]) ^ ($box[($box[$a] + $box[$j]) % 256]));
        }
        if($operation) {
            if((substr($result, 0, 10) == 0 || substr($result, 0, 10) - time() > 0) &&
                substr($result, 10, 16) == substr(md5(substr($result, 26).$keyb), 0, 16)) {
                return substr($result, 26);
            } else {
                return '';
            }
        } else {
            return $keyc.str_replace('=', '', base64_encode($result));
        }
    }
}