using System.Linq;
using System.Security.Cryptography;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.SignalR;
using Microsoft.AspNetCore.WebUtilities;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.FileProviders;

namespace VideoDownloader.Server;

/// <summary>
/// M0 원격 접근 서버: 데스크톱 앱에 내장되는 Kestrel.
/// QR 페어링 토큰(Bearer) 인증 + 큐 API + 라이브러리/Range 스트리밍 + 제로 설치 웹 컴패니언.
/// LAN 직결(계정/클라우드 없음) — MOBILE_PLAN §3 아키텍처.
/// </summary>
public sealed class ServerHost : IAsyncDisposable
{
    private readonly WebApplication _app;
    private readonly string _token;
    private readonly ServerOptions _options;
    private readonly Action? _unsubscribeQueueChanged;
    private readonly MdnsAdvertiser? _mdns;

    public int Port { get; }
    /// <summary>QR 에 담을 페어링 URL 형식: http://&lt;lan-ip&gt;:&lt;port&gt;/#t=&lt;token&gt;</summary>
    public string Token => _token;
    /// <summary>mDNS 광고(_videodl._tcp) 동작 여부. EnableMdns=true 인데 false 면 MdnsError 를 본다.</summary>
    public bool MdnsActive => _mdns != null;
    /// <summary>mDNS 시작 실패 원인(발견 보조 기능이라 서버 기동은 막지 않고 여기로 드러냄).</summary>
    public Exception? MdnsError { get; }

    private ServerHost(WebApplication app, int port, string token, ServerOptions options,
        Action? unsubscribeQueueChanged, MdnsAdvertiser? mdns, Exception? mdnsError)
    {
        _app = app;
        Port = port;
        _token = token;
        _options = options;
        _unsubscribeQueueChanged = unsubscribeQueueChanged;
        _mdns = mdns;
        MdnsError = mdnsError;
    }

    public static async Task<ServerHost> StartAsync(ServerOptions options)
    {
        var token = string.IsNullOrEmpty(options.Token)
            ? WebEncoders.Base64UrlEncode(RandomNumberGenerator.GetBytes(32))
            : options.Token;

        var builder = WebApplication.CreateBuilder(new WebApplicationOptions { Args = new[] { "--urls", $"http://0.0.0.0:{(options.Port == 0 ? GetFreePort() : options.Port)}" } });
        foreach (var prov in builder.Services.Where(sd => sd.ServiceType.FullName!.Contains("LoggerProvider")).ToList())
            builder.Services.Remove(prov);
        builder.Services.AddSingleton<IQueueAdapter>(options.Queue);
        builder.Services.AddSignalR();

        var app = builder.Build();
        app.UseWebSockets(); // SignalR 웹소켓 전송용 (없으면 롱폴링만 됨)

        // Bearer 토큰 인증(상수시간 비교) — / 와 /api/* 전체 적용
        app.Use(async (ctx, next) =>
        {
            if (!ctx.Request.Path.StartsWithSegments("/api/pair") &&
                (ctx.Request.Path.StartsWithSegments("/api") || ctx.Request.Path.StartsWithSegments("/stream") ||
                 ctx.Request.Path.StartsWithSegments("/file") || ctx.Request.Path.StartsWithSegments("/hubs")))
            {
                var auth = ctx.Request.Headers.Authorization.ToString();
                var provided = auth.StartsWith("Bearer ", StringComparison.OrdinalIgnoreCase) ? auth[7..].Trim() : "";
                // <video>/<a> 태그는 헤더를 못 실음 → 쿼리 토큰도 허용(LAN 한정)
                if (provided.Length == 0 && ctx.Request.Query.TryGetValue("t", out var q)) provided = q.ToString();
                // SignalR 클라이언트 관례(AccessTokenProvider)는 access_token 쿼리로 실어 보냄
                if (provided.Length == 0 && ctx.Request.Query.TryGetValue("access_token", out var at)) provided = at.ToString();
                if (!FixedTimeEquals(provided, token))
                {
                    ctx.Response.StatusCode = StatusCodes.Status401Unauthorized;
                    return;
                }
            }
            await next();
        });

        // ── 페어링 ──
        app.MapPost("/api/pair", async (HttpContext ctx) =>
        {
            var body = await ctx.Request.ReadFromJsonAsync<PairRequest>();
            if (body == null || !FixedTimeEquals(body.Token ?? "", token))
            {
                ctx.Response.StatusCode = StatusCodes.Status401Unauthorized;
                return;
            }
            await ctx.Response.WriteAsJsonAsync(new { ok = true, device = options.DeviceName });
        });

        // ── 큐 ──
        var queue = options.Queue;
        app.MapGet("/api/queue", async (HttpContext ctx) =>
            await ctx.Response.WriteAsJsonAsync(await queue.GetItemsAsync()));

        app.MapPost("/api/queue", async (HttpContext ctx) =>
        {
            var body = await ctx.Request.ReadFromJsonAsync<QueueAddRequest>();
            if (body == null || !Uri.TryCreate(body.Url, UriKind.Absolute, out _))
            {
                ctx.Response.StatusCode = StatusCodes.Status400BadRequest;
                return;
            }
            var id = await queue.AddAsync(body.Url, body.Title);
            await ctx.Response.WriteAsJsonAsync(new { id });
        });

        app.MapPost("/api/queue/{id}/pause", async (string id) => { await queue.PauseAsync(id); Results.Ok(); });
        app.MapPost("/api/queue/{id}/resume", async (string id) => { await queue.ResumeAsync(id); Results.Ok(); });
        app.MapPost("/api/queue/{id}/cancel", async (string id) => { await queue.CancelAsync(id); Results.Ok(); });

        // ── 라이브러리 / 스트리밍 ──
        // ── 라이브러리 + 썸네일/해상도(M2) ──
        var thumbnailer = options.Thumbnailer ?? ServerOptionsDefaults.DefaultThumbnailer();
        var ffmpeg = options.FfmpegPath ?? VideoDownloader.Core.Platform.DesktopMediaMuxer.Default.ResolveFfmpeg(new VideoDownloader.Core.Config.AppConfig());
        app.MapGet("/api/library", async (HttpContext ctx) =>
        {
            var items = MediaLibrary.List(options.LibraryFolder);
            if (ffmpeg != null)
            {
                for (var i = 0; i < items.Count; i++)
                {
                    var res = await thumbnailer.GetResolutionAsync(ffmpeg, Path.Combine(options.LibraryFolder, items[i].FileName));
                    items[i] = items[i] with { Resolution = res };
                }
            }
            await ctx.Response.WriteAsJsonAsync(items);
        });

        app.MapGet("/api/library/{id}/thumb", async (string id) =>
        {
            var file = MediaLibrary.Find(options.LibraryFolder, id);
            if (file == null || ffmpeg == null) return Results.NotFound();
            var jpg = await thumbnailer.GetThumbnailAsync(ffmpeg, file.Value.FullPath);
            return jpg == null ? Results.NotFound() : Results.File(jpg, "image/jpeg");
        });

        app.MapGet("/stream/{id}", (string id) =>
        {
            var file = MediaLibrary.Find(options.LibraryFolder, id);
            return file == null
                ? Results.NotFound()
                : Results.File(file.Value.FullPath, "video/mp4", enableRangeProcessing: true); // 206 Partial Content → 시크 지원
        });

        app.MapGet("/file/{id}", (string id) =>
        {
            var file = MediaLibrary.Find(options.LibraryFolder, id);
            return file == null ? Results.NotFound() : Results.File(file.Value.FullPath, "application/octet-stream", file.Value.FileName);
        });

        // ── 이어보기 위치 동기화 (U3) ──
        var positions = new PositionStore(options.LibraryFolder);
        app.MapGet("/api/position/{id}", (string id) => Results.Json(new PositionDto(positions.Get(id))));
        app.MapPost("/api/position/{id}", async (string id, HttpContext ctx) =>
        {
            var body = await ctx.Request.ReadFromJsonAsync<PositionDto>();
            if (body == null) return Results.BadRequest();
            positions.Set(id, body.PositionSec);
            return Results.Ok();
        });

        // ── 실시간 큐 허브 (MOBILE_PLAN §3 /hubs/queue) ──
        app.MapHub<QueueHub>("/hubs/queue");
        var hubContext = app.Services.GetRequiredService<Microsoft.AspNetCore.SignalR.IHubContext<QueueHub>>();
        Action onQueueChanged = () => _ = BroadcastQueueAsync(hubContext, queue);
        queue.Changed += onQueueChanged;

        // ── 웹 컴패니언 (제로 설치 클라이언트) ──
        app.MapGet("/", () => Results.Text(WebCompanion.Html, "text/html; charset=utf-8"));

        await app.StartAsync();
        var actualPort = options.Port;
        if (actualPort == 0)
        {
            var m = app.Urls.SelectMany(u => System.Text.RegularExpressions.Regex.Matches(u, @":(\d+)"))
                            .Select(m2 => int.Parse(m2.Groups[1].Value)).FirstOrDefault();
            actualPort = m;
        }

        // ── mDNS 광고 (_videodl._tcp) — 발견 보조. 실패는 MdnsError 로 드러내되 서버는 유지 ──
        MdnsAdvertiser? mdns = null;
        Exception? mdnsError = null;
        if (options.EnableMdns)
        {
            try
            {
                mdns = new MdnsAdvertiser(options.DeviceName, actualPort);
                mdns.Start();
            }
            catch (Exception ex)
            {
                mdnsError = ex;
                mdns?.Dispose();
                mdns = null;
            }
        }

        return new ServerHost(app, actualPort, token, options, () => queue.Changed -= onQueueChanged, mdns, mdnsError);
    }

    /// <summary>큐 변경 → 전 클라이언트 푸시. 종료 경합만 무시(그 외 실패는 UnobservedTaskException 로 관찰됨).</summary>
    private static async Task BroadcastQueueAsync(Microsoft.AspNetCore.SignalR.IHubContext<QueueHub> hub, IQueueAdapter queue)
    {
        try
        {
            var items = await queue.GetItemsAsync();
            await hub.Clients.All.SendAsync("queueUpdated", items);
        }
        catch (ObjectDisposedException)
        {
            // 서버 종료와 경합한 마지막 푸시 — 클라이언트는 재접속/스냅샷으로 보정
        }
    }

    public async ValueTask DisposeAsync()
    {
        _unsubscribeQueueChanged?.Invoke();
        _mdns?.Dispose();
        await _app.StopAsync();
        await _app.DisposeAsync();
    }

    private static int GetFreePort()
    {
        using var l = new System.Net.Sockets.TcpListener(System.Net.IPAddress.Loopback, 0);
        l.Start();
        var port = ((System.Net.IPEndPoint)l.LocalEndpoint).Port;
        l.Stop();
        return port;
    }

    private static bool FixedTimeEquals(string a, string b)
    {
        var ha = SHA256.HashData(System.Text.Encoding.UTF8.GetBytes(a));
        var hb = SHA256.HashData(System.Text.Encoding.UTF8.GetBytes(b));
        return CryptographicOperations.FixedTimeEquals(ha, hb);
    }

    private sealed record PairRequest(string? Token, string? Device);
    private sealed record QueueAddRequest(string Url, string? Title);
}