using System.Diagnostics;
using System.Text.Json;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;

namespace ThingHK;

/// <summary>
/// HTTP 服务层：minimal API 风格扩展方法。
/// 路由设计（见 ThingHK_GUIDE.md 第 2.3 节）：
///   GET  /status   → 冷启动就绪探测，前端轮询判断是否可订阅
///   GET  /snapshot → 一次性拉取最新缓存快照
///   GET  /stream   → SSE 订阅，Kernel 主动推送 SensorSnapshot
///   POST /config   → 运行时调整采样间隔
///   GET  /         → 健康检查（200 OK）
/// </summary>
internal static class HttpEndpoints
{
    public static WebApplication MapThingHKEndpoints(this WebApplication app, KernelHost kernel)
    {
        // 全局异常捕获中间件：把未处理异常写到 stderr，便于 AOT 下排错
        app.Use(async (ctx, next) =>
        {
            try { await next(); }
            catch (Exception ex)
            {
                Console.Error.WriteLine($"[HTTP] {ctx.Request.Method} {ctx.Request.Path} 异常: {ex}");
                ctx.Response.StatusCode = 500;
                await ctx.Response.WriteAsync($"{{\"error\":\"internal\",\"message\":\"{ex.Message.Replace("\"", "\\\"")}\"}}");
            }
        });

        // 根路由：进程存活检查（curl 友好）
        // AOT 下必须用 Results.Json + TypeInfo，Results.Ok(object) 会走默认 options 抛 JsonTypeInfo 异常
        app.MapGet("/", () => Results.Json(new HealthResponse(), ThingHKJsonContext.Default.HealthResponse));

        // 冷启动就绪探测
        app.MapGet("/status", () =>
        {
            var hw = kernel.Hardware;
            var snap = kernel.Scheduler.Cache.GetLatest();
            var status = new KernelStatus
            {
                Ready = hw?.Ready ?? false,
                IsAdmin = hw?.IsAdmin ?? false,
                UptimeMs = kernel.Uptime.Elapsed.TotalMilliseconds,
                GroupCount = snap?.Groups.Count ?? 0,
                SensorCount = kernel.Scheduler.Cache.SensorCount,
                Providers = snap?.Groups.Select(g => g.Id).ToList() ?? new List<string>(),
            };
            return Results.Json(status, ThingHKJsonContext.Default.KernelStatus);
        });

        // 一次性快照
        app.MapGet("/snapshot", (HttpContext ctx) =>
        {
            var snap = kernel.Scheduler.Cache.GetLatest();
            if (snap == null)
            {
                ctx.Response.StatusCode = 404;
                return Results.Json(new ErrorResponse("not_ready", "Kernel 尚未完成首轮扫描"), ThingHKJsonContext.Default.ErrorResponse);
            }
            return Results.Json(snap, ThingHKJsonContext.Default.SensorSnapshot);
        });

        // SSE 推送流
        app.MapGet("/stream", async (HttpContext ctx, CancellationToken ct) =>
        {
            // 强制 text/event-stream，禁用响应缓冲（SSE 必须 flush）
            ctx.Response.ContentType = "text/event-stream";
            ctx.Response.Headers.CacheControl = "no-cache";
            ctx.Response.Headers.Connection = "keep-alive";
            ctx.Response.Headers["X-Accel-Buffering"] = "no";

            // 先推一次当前缓存快照，避免客户端等待一个 tick 才有数据
            var initial = kernel.Scheduler.Cache.GetLatest();
            if (initial != null)
            {
                await WriteSseEventAsync(ctx, initial, ct).ConfigureAwait(false);
            }

            // 订阅广播
            await foreach (var snap in kernel.Scheduler.SubscribeAsync(ct).ConfigureAwait(false))
            {
                await WriteSseEventAsync(ctx, snap, ct).ConfigureAwait(false);
            }
        });

        // 运行时配置调整
        // 注意：async lambda 必须返回 Task<IResult>，单纯返回 IResult 会被框架当成 Task<IResult> 的未等待任务，导致响应体为空
        app.MapPost("/config", async Task<IResult> (HttpContext ctx) =>
        {
            // 先读 body 为字符串，再反序列化。
            // 在 AOT 下比 DeserializeAsync 对 nullable 属性更稳定。
            using var reader = new StreamReader(ctx.Request.Body);
            var body = await reader.ReadToEndAsync(ctx.RequestAborted);
            ConfigRequest? req;
            try
            {
                req = string.IsNullOrWhiteSpace(body)
                    ? new ConfigRequest()
                    : JsonSerializer.Deserialize(body, ThingHKJsonContext.Default.ConfigRequest);
            }
            catch (JsonException ex)
            {
                ctx.Response.StatusCode = 400;
                return Results.Json(new ErrorResponse("invalid_json", ex.Message), ThingHKJsonContext.Default.ErrorResponse);
            }
            if (req == null)
            {
                ctx.Response.StatusCode = 400;
                return Results.Json(new ErrorResponse("invalid_body", "请求体为空"), ThingHKJsonContext.Default.ErrorResponse);
            }

            kernel.Scheduler.UpdateIntervals(req.FastIntervalMs, req.SlowIntervalMs);
            return Results.Json(new ConfigResponse
            {
                Success = true,
                FastIntervalMs = kernel.Scheduler.FastIntervalMs,
                SlowIntervalMs = kernel.Scheduler.SlowIntervalMs,
                StreamIntervalMs = kernel.Scheduler.FastIntervalMs,
            }, ThingHKJsonContext.Default.ConfigResponse);
        });

        return app;
    }

    /// <summary>
    /// 写一条 SSE 事件：event: snapshot\ndata: {json}\n\n
    /// </summary>
    private static async Task WriteSseEventAsync(HttpContext ctx, SensorSnapshot snap, CancellationToken ct)
    {
        await ctx.Response.WriteAsync("event: snapshot\n", ct).ConfigureAwait(false);
        await ctx.Response.WriteAsync("data: ", ct).ConfigureAwait(false);
        // 直接用流式序列化，避免大字符串分配
        await JsonSerializer.SerializeAsync(
            ctx.Response.Body, snap, ThingHKJsonContext.Default.SensorSnapshot, ct).ConfigureAwait(false);
        await ctx.Response.WriteAsync("\n\n", ct).ConfigureAwait(false);
        await ctx.Response.Body.FlushAsync(ct).ConfigureAwait(false);
    }
}

/// <summary>
/// Kernel 宿主：持有 HardwareManager + SamplingScheduler，管理整体生命周期。
/// Program.cs 构造此对象并注入到 DI 容器供 endpoint 使用。
/// </summary>
internal sealed class KernelHost : IDisposable
{
    public HardwareManager? Hardware { get; private set; }
    public SamplingScheduler Scheduler { get; private set; } = null!;
    public Stopwatch Uptime { get; } = Stopwatch.StartNew();

    public async Task StartAsync(bool basic, int fastMs, int slowMs)
    {
        // 1. 初始化硬件层（含首轮 Update，约 5 秒）
        Hardware = new HardwareManager(basic);
        Console.Error.WriteLine($"[ThingHK] 硬件就绪: {Hardware.AllHardware.Count} 设备, 冷启动 {Hardware.ColdStartMs:F0}ms, admin={Hardware.IsAdmin}");

        // 2. 启动采样调度器（会立即推送首个快照到广播 channel）
        Scheduler = new SamplingScheduler(Hardware, fastMs, slowMs);
        await Scheduler.StartAsync();
        Console.Error.WriteLine($"[ThingHK] 调度器已启动: fast={Scheduler.FastIntervalMs}ms slow={Scheduler.SlowIntervalMs}ms");
    }

    public void Dispose()
    {
        Console.Error.WriteLine("[ThingHK] Kernel 正在关闭...");
        Scheduler?.Dispose();
        Hardware?.Dispose();
    }
}