<?php
/**
 * 加密解密類
 * 該算法僅支持加密數(shù)字。比較適用于數(shù)據(jù)庫(kù)中id字段的加密解密，以及根據(jù)數(shù)字顯示url的加密。
 * @author 深秋的竹子
 * @version alpha
 * @加密原則 標(biāo)記長(zhǎng)度 + 補(bǔ)位 + 數(shù)字替換
 * @加密步驟：
 * 將a-z,A-Z,0-9 62個(gè)字符打亂，取前M(數(shù)字最大的位數(shù))位作為 標(biāo)記長(zhǎng)度字符串，取第M+1 到第M+10位為數(shù)字替換字符串，剩余的為補(bǔ)位字符串
 * 1.計(jì)算數(shù)字長(zhǎng)度n,取亂碼的第n位作為標(biāo)記長(zhǎng)度。
 * 2.計(jì)算補(bǔ)位的長(zhǎng)度，加密串的長(zhǎng)度N -1 - n 為補(bǔ)位的長(zhǎng)度。根據(jù)指定的算法得到補(bǔ)位字符串。
 * 3.根據(jù)數(shù)字替換字符串替換數(shù)字，得到數(shù)字加密字符串。
 * 標(biāo)記長(zhǎng)度字符 + 補(bǔ)位字符串 + 數(shù)字加密字符串 = 加密串
 * Usage:
 *   $obj = new XDeode(9);
 *   $e_txt = $obj->encode(123);
 *   echo $e_txt.'<br/>';
 *   echo $key->decode($e_txt);
 */

class XDeode{
  private $strbase = "Flpvf70CsakVjqgeWUPXQxSyJizmNH6B1u3b8cAEKwTd54nRtZOMDhoG2YLrI";
  private $key,$length,$codelen,$codenums,$codeext;
  function __construct($length = 9,$key = 2543.5415412812){
    $this->key = $key;
    $this->length = $length;
    $this->codelen = substr($this->strbase,0,$this->length);
    $this->codenums = substr($this->strbase,$this->length,10);
    $this->codeext = substr($this->strbase,$this->length + 10);
  }

  function encode($nums){
    $rtn = "";
    $numslen = strlen($nums);
    //密文第一位標(biāo)記數(shù)字的長(zhǎng)度
    $begin = substr($this->codelen,$numslen - 1,1);

    //密文的擴(kuò)展位
    $extlen = $this->length - $numslen - 1;
    $temp = str_replace('.', '', $nums / $this->key);
    $temp = substr($temp,-$extlen);

    $arrextTemp = str_split($this->codeext);
    $arrext = str_split($temp);
    foreach ($arrext as $v) {
      $rtn .= $arrextTemp[$v];
    }

    $arrnumsTemp = str_split($this->codenums);
    $arrnums = str_split($nums);
    foreach ($arrnums as $v) {
      $rtn .= $arrnumsTemp[$v];
    }
    return $begin.$rtn;
  }

  function decode($code){

    $begin = substr($code,0,1);
    $rtn = '';
    $len = strpos($this->codelen,$begin);
    if($len!== false){
      $len++;
      $arrnums = str_split(substr($code,-$len));
      foreach ($arrnums as $v) {
        $rtn .= strpos($this->codenums,$v);
      }
    }

    return $rtn;
  }
}

/**** 示例  ****/
$begin = 9950;
$end = $begin + 50;
$obj = new XDeode(9);
for($i=$begin;$i<$end;$i++){
  $en = $obj->encode($i);
  $de = $obj->decode($en);
  echoln("[{$i}]=[{$en}]=[{$de}]");
}

function echoln($str){
  echo "{$str}<br/>";
}
?>