using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Runtime.Serialization;
using System.Threading.Tasks;
using System.Xml.Serialization;
using NewLife.Configuration;
using NewLife.Data;
using NewLife.Http;
using NewLife.Log;
using NewLife.Model;

namespace NewLife.Remoting
{
    /// <summary>Http应用接口客户端</summary>
    public class ApiHttpClient : DisposeBase, IApiClient, IConfigMapping
    {
        #region 属性
        /// <summary>令牌。每次请求携带</summary>
        public String Token { get; set; }

        /// <summary>超时时间。默认15000ms</summary>
        public Int32 Timeout { get; set; } = 15_000;

        /// <summary>是否使用系统代理设置。默认false不检查系统代理设置，在某些系统上可以大大改善初始化速度</summary>
        public Boolean UseProxy { get; set; }

        /// <summary>加权轮询负载均衡。默认false只使用故障转移</summary>
        public Boolean RoundRobin { get; set; }

        /// <summary>不可用节点的屏蔽时间。默认60秒</summary>
        public Int32 ShieldingTime { get; set; } = 60;

        /// <summary>身份验证</summary>
        public AuthenticationHeaderValue Authentication { get; set; }

        /// <summary>Http过滤器</summary>
        public IHttpFilter Filter { get; set; }

        /// <summary>服务器源。正在使用的服务器</summary>
        public String Source { get; private set; }

        /// <summary>调用统计</summary>
        public ICounter StatInvoke { get; set; }

        /// <summary>慢追踪。远程调用或处理时间超过该值时，输出慢调用日志，默认5000ms</summary>
        public Int32 SlowTrace { get; set; } = 5_000;

        /// <summary>跟踪器</summary>
        public ITracer Tracer { get; set; }

        /// <summary>服务列表。用于负载均衡和故障转移</summary>
        public IList<Service> Services { get; set; } = new List<Service>();

        /// <summary>当前服务</summary>
        protected Service _currentService;
        #endregion

        #region 构造
        /// <summary>实例化</summary>
        public ApiHttpClient() { }

        /// <summary>实例化</summary>
        /// <param name="urls">地址集合。多地址逗号分隔，支持权重，test1=3*http://127.0.0.1:1234,test2=7*http://127.0.0.1:3344</param>
        public ApiHttpClient(String urls) => Init(urls);

        /// <summary>按照配置服务实例化，用于NETCore依赖注入</summary>
        /// <param name="provider">服务提供者，将要解析IConfigProvider</param>
        /// <param name="name">缓存名称，也是配置中心key</param>
        public ApiHttpClient(IServiceProvider provider, String name)
        {
            //Name = name;

            var configProvider = provider.GetRequiredService<IConfigProvider>();
            configProvider.Bind(this, true, name);
        }

        ///// <summary>销毁</summary>
        ///// <param name="disposing"></param>
        //protected override void Dispose(Boolean disposing)
        //{
        //    base.Dispose(disposing);

        //    foreach (var item in Services)
        //    {
        //        item.Client?.TryDispose();
        //    }
        //}
        #endregion

        #region 方法
        /// <summary>添加服务地址</summary>
        /// <param name="name">名称</param>
        /// <param name="address">地址，支持名称和权重，test1=3*http://127.0.0.1:1234</param>
        public void Add(String name, String address) => ParseAndAdd(Services, name, address);

        /// <summary>添加服务地址</summary>
        /// <param name="name"></param>
        /// <param name="address"></param>
        public void Add(String name, Uri address) => Services.Add(new Service { Name = name, Address = address });

        private void ParseAndAdd(IList<Service> services, String name, String address)
        {
            var url = address;
            var svc = new Service
            {
                Name = name
            };

            // 解析名称
            var p = url.IndexOf('=');
            if (p > 0)
            {
                svc.Name = url[..p];
                url = url[(p + 1)..];
            }

            // 解析权重
            p = url.IndexOf("*http");
            if (p > 0)
            {
                svc.Weight = url[..p].ToInt();
                url = url[(p + 1)..];
            }

            svc.Address = new Uri(url);
            services.Add(svc);
        }

        private String _lastUrls;
        private void Init(String urls)
        {
            if (!urls.IsNullOrEmpty() && urls != _lastUrls)
            {
                var services = new List<Service>();
                var ss = urls.Split(',', StringSplitOptions.RemoveEmptyEntries);
                for (var i = 0; i < ss.Length; i++)
                {
                    if (!ss[i].IsNullOrEmpty()) ParseAndAdd(services, "service" + (i + 1), ss[i]);
                }
                Services = services;
                _lastUrls = urls;
            }
        }

        void IConfigMapping.MapConfig(IConfigProvider provider, IConfigSection section)
        {
            if (section != null && section.Value != null) Init(section.Value);
        }
        #endregion

        #region 核心方法
        /// <summary>异步获取，参数构造在Url</summary>
        /// <param name="action">服务操作</param>
        /// <param name="args">参数</param>
        /// <returns></returns>
        public async Task<TResult> GetAsync<TResult>(String action, Object args = null) => await InvokeAsync<TResult>(HttpMethod.Get, action, args);

        /// <summary>同步获取，参数构造在Url</summary>
        /// <param name="action">服务操作</param>
        /// <param name="args">参数</param>
        /// <returns></returns>
        public TResult Get<TResult>(String action, Object args = null) => Task.Run(() => GetAsync<TResult>(action, args)).Result;

        /// <summary>异步提交，参数Json打包在Body</summary>
        /// <param name="action">服务操作</param>
        /// <param name="args">参数</param>
        /// <returns></returns>
        public async Task<TResult> PostAsync<TResult>(String action, Object args = null) => await InvokeAsync<TResult>(HttpMethod.Post, action, args);

        /// <summary>同步提交，参数Json打包在Body</summary>
        /// <param name="action">服务操作</param>
        /// <param name="args">参数</param>
        /// <returns></returns>
        public TResult Post<TResult>(String action, Object args = null) => Task.Run(() => PostAsync<TResult>(action, args)).Result;

        /// <summary>异步调用，等待返回结果</summary>
        /// <typeparam name="TResult"></typeparam>
        /// <param name="method">请求方法</param>
        /// <param name="action">服务操作</param>
        /// <param name="args">参数</param>
        /// <param name="onRequest">请求头回调</param>
        /// <returns></returns>
        public virtual async Task<TResult> InvokeAsync<TResult>(HttpMethod method, String action, Object args = null, Action<HttpRequestMessage> onRequest = null)
        {
            var returnType = typeof(TResult);
            var svrs = Services;

            var i = 0;
            do
            {
                // 建立请求
                var request = BuildRequest(method, action, args, returnType);
                onRequest?.Invoke(request);

                var filter = Filter;
                try
                {
                    var msg = await SendAsync(request);

                    return await ApiHelper.ProcessResponse<TResult>(msg);
                }
                catch (Exception ex)
                {
                    while (ex is AggregateException age) ex = age.InnerException;

                    if (ex is ApiException)
                    {
                        if (filter != null) await filter.OnError(_currentService?.Client, ex, this);

                        ex.Source = _currentService?.Address + "/" + action;
                        throw;
                    }
                    else if (ex is HttpRequestException or TaskCanceledException)
                    {
                        if (filter != null) await filter.OnError(_currentService?.Client, ex, this);
                        if (++i >= svrs.Count) throw;
                    }
                    else
                        throw;
                }
            } while (true);
        }

        /// <summary>异步调用，等待返回结果</summary>
        /// <typeparam name="TResult"></typeparam>
        /// <param name="action">服务操作</param>
        /// <param name="args">参数</param>
        /// <returns></returns>
        async Task<TResult> IApiClient.InvokeAsync<TResult>(String action, Object args) => await InvokeAsync<TResult>(args == null ? HttpMethod.Get : HttpMethod.Post, action, args);

        /// <summary>同步调用，阻塞等待</summary>
        /// <param name="action">服务操作</param>
        /// <param name="args">参数</param>
        /// <returns></returns>
        TResult IApiClient.Invoke<TResult>(String action, Object args) => Task.Run(() => InvokeAsync<TResult>(args == null ? HttpMethod.Get : HttpMethod.Post, action, args)).Result;
        #endregion

        #region 构造请求
        /// <summary>建立请求</summary>
        /// <param name="method">请求方法</param>
        /// <param name="action"></param>
        /// <param name="args"></param>
        /// <param name="returnType"></param>
        /// <returns></returns>
        protected virtual HttpRequestMessage BuildRequest(HttpMethod method, String action, Object args, Type returnType)
        {
            var request = ApiHelper.BuildRequest(method, action, args);

            // 指定返回类型
            if (returnType == typeof(Byte[]) || returnType == typeof(Packet))
                request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/octet-stream"));
            else
                request.Headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

            // 加上令牌或其它身份验证
            var auth = Authentication;
            if (auth == null && !Token.IsNullOrEmpty()) auth = new AuthenticationHeaderValue("Bearer", Token);
            if (auth != null) request.Headers.Authorization = auth;

            return request;
        }
        #endregion

        #region 调度池
        /// <summary>调度索引，当前使用该索引处的服务</summary>
        private volatile Int32 _idxServer;

        /// <summary>异步发送</summary>
        /// <param name="request">请求</param>
        /// <returns></returns>
        protected virtual async Task<HttpResponseMessage> SendAsync(HttpRequestMessage request)
        {
            if (Services.Count == 0) throw new InvalidOperationException("未添加服务地址！");

            // 获取一个处理当前请求的服务，此处实现负载均衡LoadBalance和故障转移Failover
            var service = GetService();
            Source = service.Name;
            _currentService = service;

            // 性能计数器，次数、TPS、平均耗时
            var st = StatInvoke;
            var sw = st.StartCount();
            Exception error = null;
            try
            {
                var client = service.Client;
                if (client == null)
                {
                    if (service.CreateTime.Year < 2000) WriteLog("使用[{0}]：{1}", service.Name, service.Address);

                    client = CreateClient();
                    client.BaseAddress = service.Address;
                    service.Client = client;
                    service.CreateTime = DateTime.Now;
                }

                return await SendOnServiceAsync(request, service, client);
            }
            catch (Exception ex)
            {
                error = ex;

                throw;
            }
            finally
            {
                var msCost = st.StopCount(sw) / 1000;
                if (SlowTrace > 0 && msCost >= SlowTrace) WriteLog($"慢调用[{request.RequestUri.AbsoluteUri}]，耗时{msCost:n0}ms");

                // 归还服务
                PutService(service, error);
            }
        }

        /// <summary>获取一个服务用于处理请求，此处可实现负载均衡LoadBalance。默认取当前可用服务</summary>
        /// <remarks>
        /// 如需实现负载均衡，每次取值后都累加索引，让其下一次记获取时拿到下一个服务。
        /// </remarks>
        /// <returns></returns>
        protected virtual Service GetService()
        {
            // 在可用服务节点中选择，如果全部节点不可用，则启用全部节点，避免网络恢复后无法及时通信
            var svrs = Services;
            //if (!svrs.Any(e => e.NextTime < DateTime.Now)) throw new XException("没有可用服务节点！");
            if (!svrs.Any(e => e.NextTime < DateTime.Now))
            {
                foreach (var item in svrs)
                {
                    item.NextTime = DateTime.MinValue;
                }
            }

            if (RoundRobin)
            {
                // 判断当前节点是否有效
                Service svc = null;
                for (var i = 0; i < svrs.Count; i++)
                {
                    svc = svrs[_idxServer % svrs.Count];

                    // 权重足够，又没有错误，就是它了
                    if ((svc.Weight <= 0 || svc.Index < svc.Weight || svrs.Count == 1) && svc.NextTime < DateTime.Now) break;

                    // 这个就算了，再下一个
                    svc.Index = 0;
                    svc = null;
                    _idxServer++;
                }
                // 如果都没有可用节点，默认选第一个
                if (svc == null && svrs.Count > 0) svc = svrs[0];
                //if (svc == null) throw new XException("没有可用服务节点！");

                svc.Times++;

                // 计算下一次节点
                svc.Index++;
                if (svc.Index >= svc.Weight)
                {
                    svc.Index = 0;
                    _idxServer++;
                }
                if (_idxServer >= svrs.Count) _idxServer = 0;

                return svc;
            }
            else
            {
                // 一定时间后，切换回来主节点
                var idx = _idxServer;
                if (idx > 0 && svrs[0].NextTime < DateTime.Now) idx = _idxServer = 0;

                var svc = svrs[idx % svrs.Count];
                svc.Times++;

                return svc;
            }
        }

        /// <summary>归还服务，此处实现故障转移Failover，服务的客户端被清空，说明当前服务不可用</summary>
        /// <param name="service"></param>
        /// <param name="error"></param>
        protected virtual void PutService(Service service, Exception error)
        {
            if (service.CreateTime.AddMinutes(10) < DateTime.Now) service.Client = null;

            var ex = error;
            while (ex is AggregateException age) ex = age.InnerException;

            if (ex is HttpRequestException or TaskCanceledException)
            {
                // 网络异常时，自动切换到其它节点
                _idxServer++;
            }
            if (error != null)
            {
                service.Errors++;
                service.Client = null;
                service.NextTime = DateTime.Now.AddSeconds(ShieldingTime);
                service.CreateTime = DateTime.MinValue;
            }
        }

        /// <summary>在指定服务地址上发生请求</summary>
        /// <param name="request">请求消息</param>
        /// <param name="service">服务名</param>
        /// <param name="client">客户端</param>
        /// <returns></returns>
        protected virtual async Task<HttpResponseMessage> SendOnServiceAsync(HttpRequestMessage request, Service service, HttpClient client)
        {
            var filter = Filter;
            if (filter != null) await filter.OnRequest(client, request, this);

            var response = await client.SendAsync(request);

            if (filter != null) await filter.OnResponse(client, response, this);

            // 业务层只会返回200 OK
            response.EnsureSuccessStatusCode();

            return response;
        }

        /// <summary>创建客户端</summary>
        /// <returns></returns>
        protected virtual HttpClient CreateClient()
        {
            HttpMessageHandler handler = new HttpClientHandler { UseProxy = UseProxy };
            if (Tracer != null) handler = new HttpTraceHandler(handler) { Tracer = Tracer };

            var client = new HttpClient(handler)
            {
                Timeout = TimeSpan.FromMilliseconds(Timeout)
            };

            // 默认UserAgent
            client.SetUserAgent();

            return client;
        }
        #endregion

        #region 内嵌
        /// <summary>服务项</summary>
        public class Service
        {
            /// <summary>名称</summary>
            public String Name { get; set; }

            /// <summary>名称</summary>
            public Uri Address { get; set; }

            /// <summary>权重。用于负载均衡，默认1</summary>
            public Int32 Weight { get; set; } = 1;

            /// <summary>轮询均衡时，本项第几次使用</summary>
            internal Int32 Index;

            /// <summary>总次数</summary>
            public Int32 Times { get; set; }

            /// <summary>错误数</summary>
            public Int32 Errors { get; set; }

            /// <summary>创建时间。每过一段时间，就清空一次客户端，让它重建连接，更新域名缓存</summary>
            [XmlIgnore, IgnoreDataMember]
            public DateTime CreateTime { get; set; }

            /// <summary>下一次时间。服务项出错时，将禁用一段时间</summary>
            [XmlIgnore, IgnoreDataMember]
            public DateTime NextTime { get; set; }

            /// <summary>客户端</summary>
            [XmlIgnore, IgnoreDataMember]
            public HttpClient Client { get; set; }

            /// <summary>已重载。友好显示</summary>
            /// <returns></returns>
            public override String ToString() => $"{Name} {Address}";
        }
        #endregion

        #region 日志
        /// <summary>日志</summary>
        public ILog Log { get; set; } = Logger.Null;

        /// <summary>写日志</summary>
        /// <param name="format"></param>
        /// <param name="args"></param>
        public void WriteLog(String format, params Object[] args) => Log?.Info(format, args);
        #endregion
    }
}