using Microsoft.Extensions.Configuration;
using Newtonsoft.Json;
using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;
using YD_WeChatApplet.WeChat.Lib;

namespace YD_WeChatApplet.WeChat
{
    /// <summary>
    /// 微信小程序登录接口
    /// </summary>
    public class WeChatAppDecrypt
    {
        // 构造函数
        // public WeChatAppDecrypt(IConfiguration configuration)
        // {
        //     Configuration = configuration;
        // }

        /// <summary>
        /// 获取OpenId和SessionKey的Json数据包
        /// </summary>
        /// <param name="code">客户端发来的code</param>
        /// <returns>Json数据包</returns>
        private string GetOpenIdAndSessionKeyString(string code, string appid, string secret)
        {
            string temp = "https://api.weixin.qq.com/sns/jscode2session?" +
                "appid=" + appid
                + "&secret=" + secret
                + "&js_code=" + code
                + "&grant_type=authorization_code";

            return HttpService.Get(temp);
        }

        /// <summary>
        /// 反序列化包含OpenId和SessionKey的Json数据包
        /// </summary>
        /// <param name="loginInfo">Json数据包</param>
        /// <returns>包含OpenId和SessionKey的类</returns>
        public OpenIdAndSessionKey DecodeOpenIdAndSessionKey(WechatLoginInfo loginInfo)
        {
            var res = GetOpenIdAndSessionKeyString(loginInfo.code, loginInfo.appid, loginInfo.secret);
            OpenIdAndSessionKey oiask = JsonConvert.DeserializeObject<OpenIdAndSessionKey>(res);
            if (!String.IsNullOrEmpty(oiask.errcode))
                return null;
            return oiask;
        }

        /// <summary>
        /// 根据微信小程序平台提供的解密算法解密数据，推荐直接使用此方法
        /// </summary>
        /// <param name="loginInfo">登陆信息</param>
        /// <returns>用户信息</returns>
        public WechatUserInfo Decrypt(WechatLoginInfo loginInfo)
        {
            if (loginInfo == null || string.IsNullOrEmpty(loginInfo.code))
                return null;

            OpenIdAndSessionKey oiask = DecodeOpenIdAndSessionKey(loginInfo);
            if (oiask == null)
                return null;

            WechatUserInfo userInfo;
            //if (!String.IsNullOrWhiteSpace(oiask.openid) && !string.IsNullOrWhiteSpace(loginInfo.rawData))
            //{
            //    userInfo = JsonConvert.DeserializeObject<WechatUserInfo>(loginInfo.rawData);
            //    userInfo.openId = oiask.openid;
            //    //userInfo.unionId = oiask.unionId;
            //    return userInfo;
            //}

            // 解密过程
            userInfo = Decrypt(loginInfo.encryptedData, loginInfo.iv, oiask.session_key);
            userInfo.openId = oiask.openid;
            return userInfo;
        }

        /// <summary>
        /// 根据微信小程序平台提供的解密算法解密数据
        /// </summary>
        /// <param name="encryptedData">加密数据</param>
        /// <param name="iv">初始向量</param>
        /// <param name="sessionKey">从服务端获取的SessionKey</param>
        /// <returns>解密后的用户信息</returns>
        public WechatUserInfo Decrypt(string encryptedData, string iv, string sessionKey)
        {
            // 创建解密器生成工具实例
            AesCryptoServiceProvider aes = new AesCryptoServiceProvider();
            aes.Mode = CipherMode.CBC;
            aes.BlockSize = 128;
            aes.Padding = PaddingMode.PKCS7;

            // 格式化待处理字符串
            byte[] byte_encryptedData = Convert.FromBase64String(encryptedData);
            byte[] byte_iv = Convert.FromBase64String(iv);
            byte[] byte_sessionKey = Convert.FromBase64String(sessionKey);

            aes.IV = byte_iv;
            aes.Key = byte_sessionKey;

            // 创建解密器
            ICryptoTransform transform = aes.CreateDecryptor(aes.Key, aes.IV);
            byte[] decryptedData;

            // 使用 CryptoStream 解密数据
            using (var ms = new MemoryStream())
            using (var cs = new CryptoStream(ms, transform, CryptoStreamMode.Write))
            {
                cs.Write(byte_encryptedData, 0, byte_encryptedData.Length);
                cs.FlushFinalBlock();
                decryptedData = ms.ToArray();
            }

            // 去除解密后的数据的填充部分
            string result = Encoding.UTF8.GetString(RemovePadding(decryptedData));

            // 反序列化并返回用户信息
            WechatUserInfo userInfo = JsonConvert.DeserializeObject<WechatUserInfo>(result);
            return userInfo;
        }

        /// <summary>
        /// 移除填充字节
        /// </summary>
        /// <param name="decrypted">解密后的数据</param>
        /// <returns>去除填充后的数据</returns>
        private static byte[] RemovePadding(byte[] decrypted)
        {
            int pad = decrypted[decrypted.Length - 1];
            if (pad < 1 || pad > 32)
            {
                pad = 0;
            }
            byte[] result = new byte[decrypted.Length - pad];
            Array.Copy(decrypted, result, result.Length);
            return result;
        }
    }
}