using System.Diagnostics;
using System.IO;
using System.Net;
using System.Text;
using System.Text.Json;
using System.Windows;
using Microsoft.Win32;

namespace OmniNotify;

public sealed class AppStore
{
    private static readonly JsonSerializerOptions JsonOptions = new() { WriteIndented = true };
    private readonly string _statePath;

    public AppStore()
    {
        var root = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "OmniNotify");
        Directory.CreateDirectory(root);
        _statePath = Path.Combine(root, "state.json");
    }

    public AppState Load()
    {
        if (!File.Exists(_statePath))
        {
            var state = new AppState();
            state.Channels.Add(new Channel { Name = "default" });
            return state;
        }

        try
        {
            return JsonSerializer.Deserialize<AppState>(File.ReadAllText(_statePath), JsonOptions) ?? new AppState();
        }
        catch
        {
            return new AppState();
        }
    }

    public void Save(AppState state)
    {
        CleanupHistory(state);
        File.WriteAllText(_statePath, JsonSerializer.Serialize(state, JsonOptions));
    }

    private static void CleanupHistory(AppState state)
    {
        var cutoff = DateTime.Now.AddDays(-Math.Max(1, state.Settings.RetainDays));
        var survivors = state.History.Where(item => item.ReceivedAt >= cutoff)
            .OrderByDescending(item => item.ReceivedAt)
            .Take(Math.Max(1, state.Settings.RetainCount))
            .OrderBy(item => item.ReceivedAt)
            .ToList();

        state.History.Clear();
        foreach (var item in survivors)
        {
            state.History.Add(item);
        }
    }
}

public sealed class NotificationRouter
{
    private readonly AppState _state;
    private readonly AppStore _store;
    private readonly PopupCoordinator _popupCoordinator;
    private readonly Queue<DateTime> _rateWindow = new();

    public event Action? StateChanged;

    public NotificationRouter(AppState state, AppStore store, PopupCoordinator popupCoordinator)
    {
        _state = state;
        _store = store;
        _popupCoordinator = popupCoordinator;
    }

    public void Receive(IncomingMessage message, bool recordHistory = true)
    {
        System.Windows.Application.Current.Dispatcher.Invoke(() =>
        {
            if (_state.Settings.CircuitBreakerOpen)
            {
                return;
            }

            if (IsRateLimited())
            {
                _state.Settings.CircuitBreakerOpen = true;
                _popupCoordinator.ShowSystem("熔断保护", "检测到大量消息，已开启熔断保护。");
                SaveAndNotify();
                return;
            }

            var channel = _state.Channels.FirstOrDefault(item =>
                string.Equals(item.Name, message.Channel, StringComparison.Ordinal));

            if (channel is null)
            {
                AddHistory(message, NotificationStatus.IllegalChannel);
                SaveAndNotify();
                return;
            }

            if (_state.Settings.DndEnabled)
            {
                AddHistory(message, NotificationStatus.DndMuted);
                SaveAndNotify();
                return;
            }

            if (recordHistory)
            {
                AddHistory(message, NotificationStatus.Displayed);
            }

            _popupCoordinator.Show(channel, message);
            SaveAndNotify();
        });
    }

    public void Replay(HistoryItem item)
    {
        var channel = _state.Channels.FirstOrDefault(candidate =>
            string.Equals(candidate.Name, item.Channel, StringComparison.Ordinal));

        if (channel is not null)
        {
            _popupCoordinator.Show(channel, new IncomingMessage { Channel = item.Channel, Title = item.Title, Body = item.Body });
        }
    }

    public void ResetCircuitBreaker()
    {
        _state.Settings.CircuitBreakerOpen = false;
        _rateWindow.Clear();
        SaveAndNotify();
    }

    private bool IsRateLimited()
    {
        var now = DateTime.Now;
        while (_rateWindow.Count > 0 && (now - _rateWindow.Peek()).TotalSeconds > 1)
        {
            _rateWindow.Dequeue();
        }

        _rateWindow.Enqueue(now);
        return _rateWindow.Count > Math.Max(1, _state.Settings.MaxMessagesPerSecond);
    }

    private void AddHistory(IncomingMessage message, NotificationStatus status)
    {
        _state.History.Add(new HistoryItem
        {
            Channel = message.Channel,
            Title = message.Title,
            Body = message.Body,
            Status = status
        });
    }

    private void SaveAndNotify()
    {
        _store.Save(_state);
        StateChanged?.Invoke();
    }
}

public sealed class LocalHttpServer : IDisposable
{
    private readonly NotificationRouter _router;
    private HttpListener? _listener;
    private CancellationTokenSource? _cts;

    public LocalHttpServer(NotificationRouter router)
    {
        _router = router;
    }

    public string? Url { get; private set; }
    public string? LastError { get; private set; }

    public void Start(int port)
    {
        Url = $"http://127.0.0.1:{port}/";
        _cts = new CancellationTokenSource();
        _listener = new HttpListener();
        _listener.Prefixes.Add(Url);

        try
        {
            _listener.Start();
            _ = ListenAsync(_cts.Token);
        }
        catch (Exception ex)
        {
            LastError = ex.Message;
        }
    }

    private async Task ListenAsync(CancellationToken token)
    {
        while (!token.IsCancellationRequested && _listener?.IsListening == true)
        {
            try
            {
                var context = await _listener.GetContextAsync();
                _ = Task.Run(() => HandleAsync(context), token);
            }
            catch when (token.IsCancellationRequested)
            {
                break;
            }
            catch (Exception ex)
            {
                LastError = ex.Message;
            }
        }
    }

    private async Task HandleAsync(HttpListenerContext context)
    {
        try
        {
            if (context.Request.HttpMethod == "GET")
            {
                await WriteAsync(context, 200, "Omni-Notify is listening. POST /notify with JSON: {\"channel\":\"default\",\"title\":\"Hi\",\"body\":\"Text\"}");
                return;
            }

            if (context.Request.HttpMethod != "POST" || context.Request.Url?.AbsolutePath != "/notify")
            {
                await WriteAsync(context, 404, "Not found");
                return;
            }

            using var reader = new StreamReader(context.Request.InputStream, context.Request.ContentEncoding);
            var body = await reader.ReadToEndAsync();
            var message = JsonSerializer.Deserialize<IncomingMessage>(body, new JsonSerializerOptions { PropertyNameCaseInsensitive = true });

            if (message is null || string.IsNullOrWhiteSpace(message.Channel))
            {
                await WriteAsync(context, 400, "Invalid message");
                return;
            }

            _router.Receive(message);
            await WriteAsync(context, 202, "Accepted");
        }
        catch (Exception ex)
        {
            await WriteAsync(context, 500, ex.Message);
        }
    }

    private static async Task WriteAsync(HttpListenerContext context, int code, string text)
    {
        var bytes = Encoding.UTF8.GetBytes(text);
        context.Response.StatusCode = code;
        context.Response.ContentType = "text/plain; charset=utf-8";
        context.Response.ContentLength64 = bytes.Length;
        await context.Response.OutputStream.WriteAsync(bytes);
        context.Response.Close();
    }

    public void Dispose()
    {
        _cts?.Cancel();
        _listener?.Close();
    }
}

public static class StartupManager
{
    private const string AppName = "OmniNotify";

    public static void Apply(bool enabled)
    {
        using var key = Registry.CurrentUser.OpenSubKey(@"Software\Microsoft\Windows\CurrentVersion\Run", true);
        if (key is null)
        {
            return;
        }

        if (enabled)
        {
            key.SetValue(AppName, Process.GetCurrentProcess().MainModule?.FileName ?? "");
        }
        else
        {
            key.DeleteValue(AppName, false);
        }
    }
}