// Middlewares/RateLimitMiddleware.cs
using AspNetCoreRateLimit;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Options;
using System;
using System.Linq;
using System.Threading.Tasks;

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

        public RateLimitMiddleware(
            RequestDelegate next,
            IMemoryCache cache,
            IOptions<RateLimitConfig> config,
            ILogger<RateLimitMiddleware> logger)
        {
            _next = next;
            _cache = cache;
            _config = config.Value;
            _logger = logger;
        }

        public async Task InvokeAsync(HttpContext context)
        {
            if (!_config.Enabled)
            {
                await _next(context);
                return;
            }

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

            // 跳过不需要限流的路径
            if (ShouldSkipRateLimit(path))
            {
                await _next(context);
                return;
            }

            // 查找匹配的配置
            EndpointRateLimit endpointConfig = null;

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

            if (endpointConfig == null)
            {
                // 使用默认配置
                if (!CheckLimit(context, "default", _config.DefaultLimit, _config.DefaultPeriod, RateLimitPolicy.IP))
                {
                    await ReturnRateLimitedResponse(context);
                    return;
                }
            }
            else
            {
                var endpointKey = $"{endpointConfig.Method}:{endpointConfig.Path}";
                if (!CheckLimit(context, endpointKey, endpointConfig.Limit, endpointConfig.Period, endpointConfig.Policy))
                {
                    await ReturnRateLimitedResponse(context, endpointConfig);
                    return;
                }
            }

            await _next(context);
        }

        private bool CheckLimit(HttpContext context, string endpointKey, int limit, int period, RateLimitPolicy policy)
        {
            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))
            {
                counter = new RateLimitCounter
                {
                    Count = 1,
                    FirstRequestTime = now,
                    LastRequestTime = now
                };

                _cache.Set(cacheKey, counter, TimeSpan.FromSeconds(period));
                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)
            {
                counter.Count = 1;
                counter.FirstRequestTime = now;
            }
            else if (counter.Count >= limit)
            {
                var remainingSeconds = (int)(counter.FirstRequestTime.AddSeconds(period) - now).TotalSeconds;
                _logger.LogWarning($"限流触发 - Endpoint: {endpointKey}, " +
                                 $"Identifier: {identifier}, " +
                                 $"Count: {counter.Count}, " +
                                 $"Limit: {limit}, " +
                                 $"Remaining: {remainingSeconds}s");
                return false;
            }
            else
            {
                counter.Count++;
            }

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

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

            configPath = configPath.ToLower();

            // 精确匹配
            if (requestPath.Equals(configPath, StringComparison.OrdinalIgnoreCase))
                return true;

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

            // 通配符匹配（简单的*通配符）
            if (configPath.Contains("*"))
            {
                var pattern = "^" + System.Text.RegularExpressions.Regex.Escape(configPath)
                    .Replace("\\*", ".*") + "$";
                return System.Text.RegularExpressions.Regex.IsMatch(requestPath, 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 async Task ReturnRateLimitedResponse(HttpContext context, EndpointRateLimit config = null)
        {
            context.Response.StatusCode = 429; // Too Many Requests
            context.Response.ContentType = "application/json";

            var message = config != null
                ? $"接口访问过于频繁，请{config.Period}秒后再试"
                : "请求过于频繁，请稍后再试";

            var response = new
            {
                Code = 429,
                Msg = message
            };

            await context.Response.WriteAsJsonAsync(response);
        }
    }

    /// <summary>
    /// 限流计数器
    /// </summary>
    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; } = 10;
        public int DefaultPeriod { get; set; } = 1;

        public List<EndpointRateLimit> Endpoints { get; set; } = new List<EndpointRateLimit>();
    }

    public class EndpointRateLimit
    {
        public string Path { get; set; }
        public string Method { get; set; } = "*";
        public int Limit { get; set; }
        public int Period { get; set; } // 秒
        public RateLimitPolicy Policy { get; set; } = RateLimitPolicy.IP;
    }
    #endregion
}