<?php
// +----------------------------------------------------------------------
// | TOPThink [ WE CAN DO IT JUST THINK ]
// +----------------------------------------------------------------------
// | Copyright (c) 2011 http://topthink.com All rights reserved.
// +----------------------------------------------------------------------
// | Licensed ( http://www.apache.org/licenses/LICENSE-2.0 )
// +----------------------------------------------------------------------
// | Author: liu21st <liu21st@gmail.com>
// +----------------------------------------------------------------------

namespace Think;

class Crypt {
    /**
     * 加密字符串
     * @access public
     * @param string $str 字符串
     * @param string $key 加密key
     * @return string
     */
    static public function encrypt($data,$key,$expire=0){
        $key  = md5($key);
        $data = base64_encode($data);
        $x    = 0;
        $len  = strlen($data);
        $l    = strlen($key);
        $char = '';
        for ($i = 0; $i< $len; $i++) {
            if ($x == $l) $x = 0;
            $char .=substr($key, $x, 1);
            $x++;
        }
        $str = sprintf('%010d', $expire ? $expire + time() : 0);
        for ($i=0; $i< $len; $i++) {
            $str .= chr(ord(substr($data, $i, 1)) + (ord(substr($char, $i, 1))) % 256);
        }
        return str_replace('=', '', base64_encode($str));
    }

    /**
     * 解密字符串
     * @access public
     * @param string $str 字符串
     * @param string $key 加密key
     * @return string
     */
    static public function decrypt($data,$key){
        $key    = md5($key);
        $x      = 0;
        $data   = base64_decode($data);
        $expire = substr($data,0,10);
        $data   = substr($data,10);
        if($expire > 0 && $expire<time()) {
            return '';
        }
        $len  = strlen($data);
        $l    = strlen($key);    
        $char = $str = '';
        for ($i=0; $i< $len; $i++) {
            if ($x == $l) $x = 0;
            $char .= substr($key, $x, 1);
            $x++;
        }
        for ($i = 0; $i < $len; $i++) {
            if (ord(substr($data, $i, 1)) < ord(substr($char, $i, 1))) {
                $str .= chr((ord(substr($data, $i, 1)) + 256) - ord(substr($char, $i, 1)));
            }else{
                $str .= chr(ord(substr($data, $i, 1)) - ord(substr($char, $i, 1)));
            }
        }
        return base64_decode($str);
    }
}