using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Http;
using System;
using System.IO;
using System.Threading.Tasks;
using YLErp.Helpers;
using YLErp.Modules.SwapModule;

namespace YLErp.Web.Middleware
{
    /// <summary>
    /// 计息计算过程追踪中间件（运行时排障用，无需重启、无需改前端）。
    ///
    /// 开启方式（三选一）：
    ///   1) 请求 URL 追加 ?swaptrace=1
    ///   2) 请求头带 X-SwapCalc-Trace: 1
    ///   3) 站点根目录 App_Data/swapcalctrace.on 标记文件存在（对所有请求开启，谨慎使用）
    ///
    /// 开启后，SwapCalcTrace 会在计息函数中逐日记录过程。本中间件在响应发出前把追踪文本写入：
    ///   - 响应头 X-SwapCalc-Trace（开发者在浏览器"网络"面板即可看到，超长则写入日志并在头部给文件路径）
    ///   - 服务器日志 logs/swapcalctrace-YYYYMMDD.log（完整文本，便于 tail/检索）
    ///
    /// 性能影响可忽略（仅被显式开启的少数请求触发，且每次只是拼字符串）。
    /// </summary>
    public class SwapCalcTraceMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly IWebHostEnvironment _env;

        public SwapCalcTraceMiddleware(RequestDelegate next, IWebHostEnvironment env)
        {
            _next = next;
            _env = env;
        }

        public async Task InvokeAsync(HttpContext context)
        {
            bool on = context.Request.Query["swaptrace"] == "1"
                      || context.Request.Headers["X-SwapCalc-Trace"] == "1";
            if (!on) on = MarkerFileExists();
            if (on) SwapCalcTrace.EnableForRequest(true);

            try
            {
                if (on)
                {
                    // OnStarting 在响应体写出前触发，确保整个请求（含计息）都已被追踪
                    context.Response.OnStarting(() =>
                    {
                        FlushTrace(context);
                        return Task.CompletedTask;
                    });
                }
                await _next(context);
            }
            finally
            {
                if (on) SwapCalcTrace.ClearForRequest();
            }
        }

        private void FlushTrace(HttpContext context)
        {
            var trace = SwapCalcTrace.DumpForRequest();
            if (string.IsNullOrEmpty(trace)) return;

            var logger = LogFactory.GetLogger("SwapCalcTrace");
            logger.Info($"[SwapCalcTrace] {context.Request.Path}\n{trace}");

            var headerVal = trace;
            if (trace.Length > 4000)
            {
                try
                {
                    var dir = Path.Combine(_env.ContentRootPath, "logs");
                    Directory.CreateDirectory(dir);
                    var file = Path.Combine(dir, $"swapcalctrace-{DateTime.Now:yyyyMMdd}.log");
                    File.AppendAllText(file,
                        $"=== {DateTime.Now:yyyy-MM-dd HH:mm:ss} {context.Request.Path} ===\n{trace}\n\n");
                    headerVal = $"(trace truncated, full in {file})\n" + trace.Substring(0, 4000);
                }
                catch
                {
                    headerVal = trace.Substring(0, 4000);
                }
            }

            try { context.Response.Headers["X-SwapCalc-Trace"] = headerVal; } catch { }
        }

        private bool MarkerFileExists()
        {
            try
            {
                return File.Exists(Path.Combine(_env.ContentRootPath, "App_Data", "swapcalctrace.on"));
            }
            catch
            {
                return false;
            }
        }
    }
}