using MAX.Framework.Dtos;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Microsoft.IO;
using System;
using System.Collections.Generic;
using System.Text;
using System.Text.Json;

namespace MAX.Framework.Commons
{
	/// <summary>
	/// 统一状态码中间件 
	/// 统一返回200 固定格式
	/// </summary>
	internal class UnifyStatusCodeMiddleware
	{

		private readonly RequestDelegate _next;
		private readonly ILogger<UnifyStatusCodeMiddleware> _logger;

		// 静态复用，全局唯一的内存池管理器
		private static readonly RecyclableMemoryStreamManager _streamManager = new();

		// 需要直接透传、不做缓冲的 Content-Type 前缀
		private static readonly string[] _passthroughPrefixes =
		{
			"image/",
			"audio/",
			"video/",
			"application/octet-stream",
			"application/zip",
			"application/pdf",
			"application/x-msdownload",
			"text/event-stream"
		};

		public UnifyStatusCodeMiddleware(RequestDelegate next, ILogger<UnifyStatusCodeMiddleware> logger)
		{
			_next = next;
			_logger = logger;
		}

		public async Task InvokeAsync(HttpContext context)
		{
			// 1. 只处理 /api 路径（按需调整或删除）
			if (!context.Request.Path.StartsWithSegments("/api"))
			{
				await _next(context);
				return;
			}

			// 2. 二进制 / 流式响应：不缓冲，直接透传
			var accept = context.Request.Headers.Accept.ToString();
			if (IsPassthroughByRequest(context) || IsPassthroughByAccept(accept))
			{
				await _next(context);
				return;
			}

			var originalBody = context.Response.Body;
			using var buffer = _streamManager.GetStream();

			context.Response.Body = buffer;

			try
			{
				await _next(context);
			}
			catch (Exception ex)
			{
				// 兜底：Filter 没抓到的异常
				_logger.LogError(ex, "未处理异常: {Path}", context.Request.Path);

				// 清空已写入的内容，准备返回 500 统一格式
				buffer.SetLength(0);
				context.Response.StatusCode = StatusCodes.Status500InternalServerError;
			}

			var statusCode = context.Response.StatusCode;
			var contentType = context.Response.ContentType ?? string.Empty;

			// 3. 响应体如果本身就是二进制/流式，透传不处理
			if (IsPassthroughByResponseContentType(contentType))
			{
				buffer.Position = 0;
				context.Response.Body = originalBody;
				await buffer.CopyToAsync(originalBody);
				return;
			}

			// 4. 2xx 且已有响应体：透传（已被 UnifyResultFilter 包装过，不再包一层）
			if (statusCode >= 200 && statusCode < 300 && buffer.Length > 0)
			{
				buffer.Position = 0;
				context.Response.Body = originalBody;
				await buffer.CopyToAsync(originalBody);
				return;
			}

			// 5. 非 2xx：统一改写为 200 + ApiResult
			var (code, msg) = MapStatusCode(statusCode);

			// 如果是 2xx 但响应体为空（少见，例如 204），也当作成功
			if (statusCode >= 200 && statusCode < 300)
			{
				code = (int)ResultCode.Success;
				msg = "success";
			}

			var result = statusCode >= 200 && statusCode < 300
				? ApiResult.Ok()
				: ApiResult.Fail(msg, code);

			// 恢复原始流并写出
			context.Response.Body = originalBody;
			context.Response.StatusCode = StatusCodes.Status200OK;
			context.Response.ContentType = "application/json; charset=utf-8";
			context.Response.ContentLength = null;

			// 清理可能存在的旧响应头
			context.Response.Headers.Remove("WWW-Authenticate");

			await context.Response.WriteAsJsonAsync(result, new JsonSerializerOptions
			{
				PropertyNamingPolicy = JsonNamingPolicy.CamelCase
			});

		}

		private static bool IsPassthroughByRequest(HttpContext context)
		{
			// 上传大文件等场景，请求体大，避免缓冲
			var contentLength = context.Request.ContentLength;
			if (contentLength.HasValue && contentLength.Value > 1_000_000) // >1MB
			{
				return true;
			}

			// Range 请求（断点续传）不缓冲
			if (context.Request.Headers.ContainsKey("Range"))
			{
				return true;
			}

			return false;
		}

		private static bool IsPassthroughByAccept(string accept)
		{
			if (string.IsNullOrEmpty(accept)) return false;

			foreach (var prefix in _passthroughPrefixes)
			{
				if (accept.Contains(prefix, StringComparison.OrdinalIgnoreCase))
					return true;
			}
			return false;
		}

		private static bool IsPassthroughByResponseContentType(string contentType)
		{
			if (string.IsNullOrEmpty(contentType)) return false;

			foreach (var prefix in _passthroughPrefixes)
			{
				if (contentType.StartsWith(prefix, StringComparison.OrdinalIgnoreCase))
					return true;
			}
			return false;
		}

		private static (int code, string msg) MapStatusCode(int statusCode) => statusCode switch
		{
			400 => ((int)ResultCode.ValidationError, "请求参数错误"),
			401 => ((int)ResultCode.Unauthorized, "未授权，请先登录"),
			403 => ((int)ResultCode.Forbidden, "禁止访问"),
			404 => ((int)ResultCode.NotFound, "资源不存在"),
			405 => ((int)ResultCode.Fail, "请求方法不允许"),
			429 => ((int)ResultCode.Fail, "请求过于频繁"),
			500 => ((int)ResultCode.ServerError, "服务器内部错误"),
			502 => ((int)ResultCode.ServerError, "网关错误"),
			503 => ((int)ResultCode.ServerError, "服务暂不可用"),
			504 => ((int)ResultCode.ServerError, "网关超时"),
			_ => ((int)ResultCode.Fail, $"请求失败({statusCode})")
		};
	}
}