using System;
using System.Collections.Concurrent;
using System.Net;
using Newtonsoft.Json;
using Common;
using System.Threading.Tasks;

namespace ZcPeng.weixin.PublicAccount
{
    /// <summary>
    /// 微信许可令牌
    /// </summary>
    public class AccessToken
    {
        /// <summary>
        /// 保存已获取到的许可令牌，键为公众号，值为公众号最后一次获取到的令牌
        /// </summary>
        private static ConcurrentDictionary<string, Tuple<AccessToken, DateTime>> accessTokens = new ConcurrentDictionary<string, Tuple<AccessToken, DateTime>>();

        /// <summary>
        /// 获取access token的地址
        /// </summary>
        private const string urlForGettingAccessToken = "https://api.weixin.qq.com/cgi-bin/token?grant_type=client_credential&appid={0}&secret={1}";
        /// <summary>
        /// 获取access token的http方法
        /// </summary>
        private const string httpMethodForGettingAccessToken = WebRequestMethods.Http.Get;
        /// <summary>
        /// 保存access token的最长时间（单位：秒），超过时间之后，需要重新获取
        /// </summary>
        private const int accessTokenSavingSeconds = 7000;

        /// <summary>
        /// access token
        /// </summary>
        public string access_token { get; set; }
        /// <summary>
        /// 有效时间，单位：秒
        /// </summary>
        public int expires_in { get; set; }

        /// <summary>
        /// 构造函数
        /// </summary>
        /// <param name="_access_token">access token</param>
        /// <param name="_expires_in">有效时间</param>
        internal AccessToken(string _access_token, int _expires_in)
        {
            access_token = _access_token;
            expires_in = _expires_in;
        }

        /// <summary>
        /// 返回AccessToken字符串
        /// </summary>
        /// <returns></returns>
        public override string ToString()
        {
            return string.Format("AccessToken：{0}\r\n有效时间：{1}秒", access_token, expires_in);
        }

        /// <summary>
        /// 从JSON字符串解析AccessToken
        /// </summary>
        /// <param name="json">JSON字符串</param>
        /// <returns>返回AccessToken</returns>
        internal static AccessToken ParseFromJson(string json)
        {
            var at = JsonConvert.DeserializeAnonymousType(json, new { access_token = "", expires_in = 1 });
            return new AccessToken(at.access_token, at.expires_in);
        }

        /// <summary>
        /// 尝试从JSON字符串解析AccessToken
        /// </summary>
        /// <param name="json">JSON字符串</param>
        /// <param name="msg">如果解析成功，返回AccessToken；否则，返回null。</param>
        /// <returns>返回是否解析成功</returns>
        internal static bool TryParseFromJson(string json, out AccessToken token)
        {
            bool success = false;
            token = null;
            try
            {
                token = ParseFromJson(json);
                success = true;
            }
            catch { }
            return success;
        }

        /// <summary>
        /// 得到access token
        /// </summary>
        /// <param name="userName">公众号</param>
        /// <returns>返回access token</returns>
        public static AccessToken Get(string userName)
        {
            Tuple<AccessToken, DateTime> lastToken = accessTokens.ContainsKey(userName) ? accessTokens[userName] : null;
            AccessToken token = lastToken == null ? null : lastToken.Item1;
            DateTime refreshTime = lastToken == null ? DateTime.MinValue : lastToken.Item2;
            if ((DateTime.Now - refreshTime).TotalSeconds > accessTokenSavingSeconds || token == null)
            {
                //尝试从微信服务器获取2次
                ErrorMessage msg;
                AccessToken newToken = GetFromWeixinServer(userName, out msg);
                if (newToken == null)
                    newToken = GetFromWeixinServer(userName, out msg);

                
                if (newToken != null)
                {
                    lastToken = new Tuple<AccessToken, DateTime>(newToken, DateTime.Now);
                    accessTokens[userName] = lastToken;
                    token = newToken;

                    Message msg1 = new Message(Guid.NewGuid(), MessageType.Request, token.ToString(),
                             DateTime.Now, "GetToken", msg.errmsg);

                    Message.Insert(msg1);
                }
                else
                {

                   Message msg1 = new Message(Guid.NewGuid(), MessageType.Request, msg.errcode == 0 ? "" : msg.errcode.ToString(),
                            DateTime.Now, "GetToken", msg.errcode+":"+msg.errmsg);

                   Message.Insert(msg1);
                   return null;
                }
            }
            return token;
        }

        /// <summary>
        /// 从微信服务器获取access token
        /// </summary>
        /// <param name="userName">公众号</param>
        /// <param name="msg">从服务器返回的错误信息。</param>
        /// <returns>返回许可令牌；如果获取失败，返回null。</returns>
        private static AccessToken GetFromWeixinServer(string userName, out ErrorMessage msg)
        {
            AccessToken token = null;
            msg = new ErrorMessage(ErrorMessage.ExceptionCode, "");
            AccountInfo account = AccountInfoCollection.GetAccountInfo(userName);
            if (account == null)
            {
                msg.errmsg = "获取公众号参数失败。";
                return token;
            }
            string url = string.Format(urlForGettingAccessToken, account.AppId, account.AppSecret);
            string result = HttpHelper.HttpPost(url,  httpMethodForGettingAccessToken, "application/text").Result;

            if(result =="")
            {
                msg.errmsg = "从微信服务器获取响应失败。";
                return token;
            }
            if (ErrorMessage.IsErrorMessage(result))
                msg = ErrorMessage.Parse(result);
            else
            {
                try
                {
                    token = AccessToken.ParseFromJson(result);
                }
                catch (Exception e)
                {
                    msg = new ErrorMessage(e);
                }
            }
            return token;
        }
    }
}