<?php

namespace wx\offiaccount\event;
use wx\offiaccount\Event\PKCS7Encoder;
use Exception;
/**
 * Prpcrypt class
 *
 * 提供接收和推送给公众平台消息的加解密接口.
 */
class Prpcrypt
{
    public $key;

    function __construct($k)
    {
        $this->key = base64_decode($k . "=");
    }

    /**
     * 对明文进行加密
     * @param string $text 需要加密的明文
     * @return string 加密后的密文
     */
    public function encrypt($text, $appid)
    {
	    try {
	        $random = $this->getRandomStr();//"aaaabbbbccccdddd";
	        $text = $random . pack("N", strlen($text)) . $text . $appid;
	        $iv = substr($this->key, 0, 16);
	        $pkc_encoder = new PKCS7Encoder();
	        $text = $pkc_encoder->encode($text);
	        $encrypted = openssl_encrypt($text,'AES-256-CBC',substr($this->key, 0, 32),OPENSSL_ZERO_PADDING,$iv);
	        return array(ErrorCode::$OK, $encrypted);
	    } catch (Exception $e) {
	        //print $e;
	        return array(ErrorCode::$EncryptAESError, null);
	    }
    }

    /**
     * 对密文进行解密
     * @param string $encrypted 需要解密的密文
     * @return string 解密得到的明文
     */
    public function decrypt($encrypted, $appid)
    {

	    try {
	        $iv = substr($this->key, 0, 16);          
	        $decrypted = openssl_decrypt($encrypted,'AES-256-CBC',substr($this->key, 0, 32),OPENSSL_ZERO_PADDING,$iv);
	    } catch (Exception $e) {
	        return array(ErrorCode::$DecryptAESError, null);
	    }
	    try {
	        //去除补位字符
	        $pkc_encoder = new PKCS7Encoder();
	        $result = $pkc_encoder->decode($decrypted);
	        //去除16位随机字符串,网络字节序和AppId
	        if (strlen($result) < 16)
	            return "";
	        $content = substr($result, 16, strlen($result));
	        $len_list = unpack("N", substr($content, 0, 4));
	        $xml_len = $len_list[1];
	        $xml_content = substr($content, 4, $xml_len);
	        $from_appid = substr($content, $xml_len + 4);
	        if (!$appid)
	            $appid = $from_appid;
	        //如果传入的appid是空的，则认为是订阅号，使用数据中提取出来的appid
	    } catch (Exception $e) {
	        //print $e;
	        return array(ErrorCode::$IllegalBuffer, null);
	    }
	    if ($from_appid != $appid)
	        return array(ErrorCode::$ValidateAppidError, null);
	    //不注释上边两行，避免传入appid是错误的情况
	    return array(0, $xml_content, $from_appid); 
	    //增加appid，为了解决后面加密回复消息的时候没有appid的订阅号会无法回复
    }


    /**
     * 随机生成16位字符串
     * @return string 生成的字符串
     */
    function getRandomStr()
    {
        $str = "";
        $str_pol = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz";
        $max = strlen($str_pol) - 1;
        for ($i = 0; $i < 16; $i++) {
            $str .= $str_pol[mt_rand(0, $max)];
        }
        return $str;
    }
}