<?php
class WeiXin
{
    /**
     * 检验数据的真实性，并且获取解密后的明文.
     * @param $encryptedData string 加密的用户数据
     * @param $iv string 与用户数据一同返回的初始向量
     * @param $data string 解密后的原文
     *
     * @return int 成功0，失败返回对应的错误码
     */
    public static function decryptData($encryptedData, $iv, $code, &$data)
    {
        $res = self::codeLogin($code);
        if (!isset($res['session_key'])) return $res;
        $sessionKey = $res['session_key'];
        if (strlen($sessionKey) != 24) return 2;
        $aesKey = base64_decode($sessionKey);
        if (strlen($iv) != 24) return 3;
        $aesIV = base64_decode($iv);
        $aesCipher = base64_decode($encryptedData);
        $result = openssl_decrypt($aesCipher, "AES-128-CBC", $aesKey, 1, $aesIV);
        $dataObj = json_decode($result);
        if ($dataObj == NULL) return 4;
        if ($dataObj->watermark->appid != env('WX_APP_ID')) return 5;
        $data = $result;
        return true;
    }

    public static function codeLogin($code)
    {
        $url = 'https://api.weixin.qq.com/sns/jscode2session?appid=' . env('WX_APP_ID') . '&secret=' . env('WX_APP_SECRET') . '&js_code=' . $code . '&grant_type=authorization_code';
        $info = file_get_contents($url);
        $json = json_decode($info);
        return get_object_vars($json);
    }
}