using IdentityModel.OidcClient;
using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Options;
using System.Text.Json;
using System.Text.Json.Serialization;

namespace OASystem.API.Middlewares
{
    public class RateLimitMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly IMemoryCache _cache;
        private readonly RateLimitConfig _config;
        private readonly ILogger<RateLimitMiddleware> _logger;
        private readonly JsonSerializerOptions _jsonOptions;

        public RateLimitMiddleware(
            RequestDelegate next,
            IMemoryCache cache,
            IOptions<RateLimitConfig> config,
            ILogger<RateLimitMiddleware> logger)
        {
            _next = next;
            _cache = cache;
            _config = config?.Value ?? new RateLimitConfig(); // 获取配置值
            _logger = logger;

            // 配置JSON序列化选项
            _jsonOptions = new JsonSerializerOptions
            {
                Encoder = System.Text.Encodings.Web.JavaScriptEncoder.UnsafeRelaxedJsonEscaping, // 允许中文
                PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
                WriteIndented = false
            };

            // 日志输出配置信息，用于调试
            LogConfiguration();
        }

        private void LogConfiguration()
        {
            _logger.LogInformation("=== 限流中间件初始化 ===");
            _logger.LogInformation($"启用状态: {_config.Enabled}");
            _logger.LogInformation($"默认限制: {_config.DefaultLimit}次/{_config.DefaultPeriod}秒");

            if (_config.Endpoints != null && _config.Endpoints.Any())
            {
                _logger.LogInformation($"配置端点数量: {_config.Endpoints.Count}");
                foreach (var endpoint in _config.Endpoints.Take(5)) // 只显示前5个
                {
                    _logger.LogInformation($"  {endpoint.Method} {endpoint.Path} -> {endpoint.Limit}次/{endpoint.Period}秒");
                }
                if (_config.Endpoints.Count > 5)
                {
                    _logger.LogInformation($"  ... 还有{_config.Endpoints.Count - 5}个配置");
                }
            }
            else
            {
                _logger.LogWarning("未配置具体端点，将使用默认规则");
            }
            _logger.LogInformation("========================");
        }

        public async Task InvokeAsync(HttpContext context)
        {
            // 记录请求开始信息（调试用）
            var requestInfo = new RequestInfo
            {
                Path = context.Request.Path,
                Method = context.Request.Method,
                ClientIp = GetClientIp(context),
                Timestamp = DateTime.UtcNow
            };

            _logger.LogDebug($"收到请求: {requestInfo.Method} {requestInfo.Path} from {requestInfo.ClientIp}");

            if (!_config.Enabled)
            {
                _logger.LogDebug("限流功能已禁用，跳过检查");
                await _next(context);
                return;
            }

            var path = context.Request.Path.ToString();
            var method = context.Request.Method.ToUpper();

            // 跳过不需要限流的路径
            if (ShouldSkipRateLimit(path))
            {
                _logger.LogDebug($"跳过限流检查: {path}");
                await _next(context);
                return;
            }

            // 查找匹配的配置
            var endpointConfig = FindMatchingConfig(path, method);

            if (endpointConfig == null)
            {
                // 使用默认配置
                _logger.LogDebug($"使用默认限流配置: {method} {path}");

                if (!CheckLimit(context, "default", _config.DefaultLimit, _config.DefaultPeriod, RateLimitPolicy.IP, requestInfo))
                {
                    await ReturnRateLimitedResponse(context, requestInfo, "默认规则");
                    return;
                }
            }
            else
            {
                var endpointKey = $"{endpointConfig.Method}:{endpointConfig.Path}";
                _logger.LogDebug($"匹配限流配置: {endpointKey} -> {endpointConfig.Limit}次/{endpointConfig.Period}秒");

                if (!CheckLimit(context, endpointKey, endpointConfig.Limit, endpointConfig.Period, endpointConfig.Policy, requestInfo))
                {
                    await ReturnRateLimitedResponse(context, requestInfo, $"{method} {path}");
                    return;
                }
            }

            _logger.LogDebug($"请求通过限流检查: {method} {path}");
            await _next(context);
        }

        private bool CheckLimit(HttpContext context, string endpointKey, int limit, int period, RateLimitPolicy policy, RequestInfo requestInfo)
        {
            var identifier = GetIdentifier(context, policy);
            var cacheKey = $"ratelimit:{endpointKey}:{identifier}";
            var now = DateTime.UtcNow;
            var windowStart = now.AddSeconds(-period);

            if (!_cache.TryGetValue<RateLimitCounter>(cacheKey, out var counter))
            {
                // 首次请求
                counter = new RateLimitCounter
                {
                    Count = 1,
                    FirstRequestTime = now,
                    LastRequestTime = now
                };

                _cache.Set(cacheKey, counter, TimeSpan.FromSeconds(period + 1));

                _logger.LogDebug($"新建限流计数器: {cacheKey}, 计数: 1/{limit}");
                return true;
            }

            // 如果第一个请求已经超过时间窗口，重置计数器
            if (counter.FirstRequestTime < windowStart)
            {
                var oldCount = counter.Count;
                counter.Count = 1;
                counter.FirstRequestTime = now;

                _logger.LogDebug($"重置限流计数器: {cacheKey}, 旧计数: {oldCount}, 新计数: 1/{limit}");
            }
            else if (counter.Count >= limit)
            {
                // 触发限流！
                var remainingSeconds = (int)(counter.FirstRequestTime.AddSeconds(period) - now).TotalSeconds;

                // 详细记录限流信息
                _logger.LogWarning($"🚫 限流触发: {requestInfo.Method} {requestInfo.Path}");
                _logger.LogWarning($"   客户端IP: {requestInfo.ClientIp}");
                _logger.LogWarning($"   标识符: {identifier}");
                _logger.LogWarning($"   规则: {endpointKey}");
                _logger.LogWarning($"   当前计数: {counter.Count}/{limit}");
                _logger.LogWarning($"   窗口开始: {counter.FirstRequestTime:HH:mm:ss}");
                _logger.LogWarning($"   剩余时间: {remainingSeconds}秒");
                _logger.LogWarning($"   用户代理: {context.Request.Headers["User-Agent"]}");

                return false;
            }
            else
            {
                // 正常计数增加
                var oldCount = counter.Count;
                counter.Count++;

                _logger.LogDebug($"增加限流计数: {cacheKey}, {oldCount} -> {counter.Count}/{limit}");
            }

            counter.LastRequestTime = now;
            _cache.Set(cacheKey, counter, TimeSpan.FromSeconds(period + 1));

            return true;
        }

        private string GetIdentifier(HttpContext context, RateLimitPolicy policy)
        {
            switch (policy)
            {
                case RateLimitPolicy.User:
                    if (context.User?.Identity?.IsAuthenticated == true)
                    {
                        var userId = context.User.FindFirst("sub")?.Value
                                  ?? context.User.FindFirst(System.Security.Claims.ClaimTypes.NameIdentifier)?.Value
                                  ?? context.User.Identity.Name;
                        return $"user_{userId}";
                    }
                    // 如果未登录，回退到IP
                    return $"ip_{context.Connection.RemoteIpAddress}";

                case RateLimitPolicy.Global:
                    return "global";

                case RateLimitPolicy.Client:
                    var clientId = context.Request.Headers["X-Client-Id"].FirstOrDefault()
                                ?? context.Request.Headers["X-API-Key"].FirstOrDefault();
                    return $"client_{clientId ?? "unknown"}";

                case RateLimitPolicy.IP:
                default:
                    var ipAddress = context.Connection.RemoteIpAddress?.ToString() ?? "unknown";
                    // 处理IPv6映射的IPv4地址
                    if (ipAddress.Contains("::ffff:"))
                    {
                        ipAddress = ipAddress.Replace("::ffff:", "");
                    }
                    return $"ip_{ipAddress}";
            }
        }

        private async Task ReturnRateLimitedResponse(HttpContext context, RequestInfo requestInfo, string ruleInfo)
        {
            context.Response.StatusCode = 429;
            context.Response.ContentType = "application/json; charset=utf-8";

            // 添加响应头信息
            context.Response.Headers.Add("X-RateLimit-Limit", "5");
            context.Response.Headers.Add("X-RateLimit-Remaining", "0");
            context.Response.Headers.Add("X-RateLimit-Reset", DateTime.UtcNow.AddSeconds(1).ToString("R"));
            context.Response.Headers.Add("X-RateLimit-Rule", ruleInfo);

            var response = new JsonView()
            {
                Code = 429,
                Msg = $"请求过于频繁（IP：{requestInfo.ClientIp}），请稍后再试！",
                Count = 0,
                Data = new
                {
                    Path = requestInfo.Path,
                    Method = requestInfo.Method,
                    ClientIp = requestInfo.ClientIp,
                    Rule = ruleInfo
                }
            };

            var json = System.Text.Json.JsonSerializer.Serialize(response, _jsonOptions);
            await context.Response.WriteAsync(json);

            // 额外记录一次限流响应日志
            _logger.LogInformation($"📤 限流响应已发送: {requestInfo.Method} {requestInfo.Path} -> 429");
        }

        private EndpointRateLimit FindMatchingConfig(string path, string method)
        {
            if (_config.Endpoints == null || !_config.Endpoints.Any())
                return null;

            foreach (var configItem in _config.Endpoints)
            {
                if (IsPathMatch(path, configItem.Path) &&
                    IsMethodMatch(method, configItem.Method))
                {
                    return configItem;
                }
            }

            return null;
        }
        private bool IsPathMatch(string requestPath, string configPath)
        {
            if (configPath == "*") return true;

            var normalizedPath = requestPath.ToLower();
            var normalizedConfigPath = configPath.ToLower();

            // 精确匹配
            if (normalizedPath.Equals(normalizedConfigPath))
                return true;

            // 前缀匹配（以/结尾表示前缀匹配）
            if (normalizedConfigPath.EndsWith("/") && normalizedPath.StartsWith(normalizedConfigPath))
                return true;

            // 通配符匹配（简单的*通配符）
            if (normalizedConfigPath.Contains("*"))
            {
                var pattern = "^" + System.Text.RegularExpressions.Regex.Escape(normalizedConfigPath)
                    .Replace("\\*", ".*") + "$";
                return System.Text.RegularExpressions.Regex.IsMatch(normalizedPath, pattern);
            }

            return false;
        }

        private bool IsMethodMatch(string requestMethod, string configMethod)
        {
            if (configMethod == "*") return true;

            return requestMethod.Equals(configMethod, StringComparison.OrdinalIgnoreCase);
        }

        private bool ShouldSkipRateLimit(string path)
        {
            // 跳过健康检查、swagger等
            var skipPaths = new[]
            {
                "/health",
                "/swagger",
                "/favicon.ico",
                "/robots.txt",
                "/.well-known"
            };

            return skipPaths.Any(p => path.StartsWith(p, StringComparison.OrdinalIgnoreCase));
        }

        private string GetClientIp(HttpContext context)
        {
            // 方法1：获取真实IP地址（处理反向代理）
            string ipAddress = string.Empty;

            // 优先从 X-Forwarded-For 获取（如果有反向代理如Nginx）
            var forwardedFor = context.Request.Headers["X-Forwarded-For"].FirstOrDefault();
            if (!string.IsNullOrEmpty(forwardedFor))
            {
                // X-Forwarded-For 可能是多个IP（client, proxy1, proxy2）
                ipAddress = forwardedFor.Split(',')[0].Trim();

                _logger.LogDebug($"从 X-Forwarded-For 获取IP: {ipAddress}");

                // 验证IP格式
                if (IsValidIpAddress(ipAddress))
                {
                    return ipAddress;
                }
            }

            // 从 X-Real-IP 获取
            var realIp = context.Request.Headers["X-Real-IP"].FirstOrDefault();
            if (!string.IsNullOrEmpty(realIp))
            {
                ipAddress = realIp.Trim();
                _logger.LogDebug($"从 X-Real-IP 获取IP: {ipAddress}");

                if (IsValidIpAddress(ipAddress))
                {
                    return ipAddress;
                }
            }

            // 从 CF-Connecting-IP 获取（Cloudflare）
            var cfConnectingIp = context.Request.Headers["CF-Connecting-IP"].FirstOrDefault();
            if (!string.IsNullOrEmpty(cfConnectingIp))
            {
                ipAddress = cfConnectingIp.Trim();
                _logger.LogDebug($"从 CF-Connecting-IP 获取IP: {ipAddress}");

                if (IsValidIpAddress(ipAddress))
                {
                    return ipAddress;
                }
            }

            // 从 X-Original-For 获取
            var originalFor = context.Request.Headers["X-Original-For"].FirstOrDefault();
            if (!string.IsNullOrEmpty(originalFor))
            {
                ipAddress = originalFor.Trim();
                _logger.LogDebug($"从 X-Original-For 获取IP: {ipAddress}");

                if (IsValidIpAddress(ipAddress))
                {
                    return ipAddress;
                }
            }

            // 最后使用 RemoteIpAddress
            ipAddress = context.Connection.RemoteIpAddress?.ToString() ?? "unknown";

            // 处理IPv6映射的IPv4地址
            if (ipAddress.Contains("::ffff:"))
            {
                ipAddress = ipAddress.Replace("::ffff:", "");
            }

            // 处理IPv6本地地址
            if (ipAddress == "::1" || ipAddress == "0:0:0:0:0:0:0:1")
            {
                ipAddress = "127.0.0.1";
            }

            _logger.LogDebug($"从 RemoteIpAddress 获取IP: {ipAddress}");

            return ipAddress;
        }

        private bool IsValidIpAddress(string ip)
        {
            if (string.IsNullOrWhiteSpace(ip))
                return false;

            if (ip.Equals("unknown", StringComparison.OrdinalIgnoreCase))
                return false;

            // 简单验证IP格式
            if (System.Net.IPAddress.TryParse(ip, out var ipAddress))
            {
                // 排除私有IP地址（如果需要）
                return !IsPrivateIp(ipAddress);
                //return true;
            }

            return false;
        }

        private bool IsPrivateIp(System.Net.IPAddress ipAddress)
        {
            // 检查是否为内网IP
            if (ipAddress.AddressFamily == System.Net.Sockets.AddressFamily.InterNetwork) // IPv4
            {
                var bytes = ipAddress.GetAddressBytes();

                // 10.0.0.0/8
                if (bytes[0] == 10)
                    return true;

                // 172.16.0.0/12
                if (bytes[0] == 172 && bytes[1] >= 16 && bytes[1] <= 31)
                    return true;

                // 192.168.0.0/16
                if (bytes[0] == 192 && bytes[1] == 168)
                    return true;

                // 127.0.0.0/8
                if (bytes[0] == 127)
                    return true;
            }
            else if (ipAddress.AddressFamily == System.Net.Sockets.AddressFamily.InterNetworkV6) // IPv6
            {
                // IPv6 本地地址
                if (ipAddress.IsIPv6LinkLocal || ipAddress.IsIPv6SiteLocal ||
                    ipAddress.IsIPv6Multicast || ipAddress.Equals(System.Net.IPAddress.IPv6Loopback))
                    return true;
            }

            return false;
        }

        // 添加 RequestInfo 辅助类
        private class RequestInfo
        {
            public string Path { get; set; }
            public string Method { get; set; }
            public string ClientIp { get; set; }
            public DateTime Timestamp { get; set; }
        }

        public class RateLimitCounter
        {
            public int Count { get; set; }
            public DateTime FirstRequestTime { get; set; }
            public DateTime LastRequestTime { get; set; }
        }
        
        #region 配置模型

        /// <summary>
        /// 限流策略枚举
        /// </summary>
        public enum RateLimitPolicy
        {
            /// <summary>
            /// 按IP地址限流
            /// </summary>
            IP = 0,

            /// <summary>
            /// 按用户限流（需要用户登录）
            /// </summary>
            User = 1,

            /// <summary>
            /// 全局限流（所有用户共享限制）
            /// </summary>
            Global = 2,

            /// <summary>
            /// 按客户端ID限流
            /// </summary>
            Client = 3
        }

        public class RateLimitConfig
        {
            public bool Enabled { get; set; } = true;
            public int DefaultLimit { get; set; } = 5;      // 默认5次/秒
            public int DefaultPeriod { get; set; } = 1;     // 默认时间窗口1秒

            [JsonPropertyName("Endpoints")]
            public List<EndpointRateLimit> Endpoints { get; set; } = new List<EndpointRateLimit>();
        }

        public class EndpointRateLimit
        {
            [JsonPropertyName("Path")]
            public string Path { get; set; } = "*";

            [JsonPropertyName("Method")]
            public string Method { get; set; } = "*";

            [JsonPropertyName("Limit")]
            public int Limit { get; set; } = 5;

            [JsonPropertyName("Period")]
            public int Period { get; set; } = 1;

            [JsonPropertyName("Policy")]
            public RateLimitPolicy Policy { get; set; } = RateLimitPolicy.IP;

            [System.Text.Json.Serialization.JsonIgnore]
            public string EndpointKey => $"{Method.ToUpper()}:{Path.ToLower()}";
        }
        #endregion
    }
}