using System.Windows.Threading;
using CursorLang.Interop;
using CursorLang.Models;

namespace CursorLang.Services;

/// <summary>
/// The settings of layout tracking.
/// </summary>
public sealed class KeyboardLayoutOptions
{
    /// <summary>How often to check the layout of the active window.</summary>
    public TimeSpan PollInterval { get; init; } = TimeSpan.FromMilliseconds(150);
}

/// <summary>
/// Polls the active window on a timer.
/// </summary>
/// <remarks>
/// Polling was chosen not for simplicity: there is no event-based way to learn about
/// a layout change in another process from managed code. HSHELL_LANGUAGE from
/// RegisterShellHookWindow does not arrive on Windows 10/11, and TSF notifications
/// (ITfLanguageProfileNotifySink) report only language changes inside our own process
/// — both options were tried and did not work. One tick is three Win32 calls reading
/// data from kernel memory.
/// </remarks>
public sealed class KeyboardLayoutService : IKeyboardLayoutService, IDisposable
{
    private readonly DispatcherTimer _pollTimer;
    private int _lastLocaleId = -1;
    private IntPtr _lastForegroundWindow;

    public KeyboardLayoutService(KeyboardLayoutOptions options)
    {
        _pollTimer = new DispatcherTimer { Interval = options.PollInterval };
        _pollTimer.Tick += OnTick;
    }

    public event EventHandler<LayoutChangedEventArgs>? LayoutChanged;

    public KeyboardLayout Current => KeyboardLayout.FromLocaleId(KeyboardLayoutNative.GetActiveLocaleId());

    public void Start()
    {
        _lastForegroundWindow = KeyboardLayoutNative.GetForegroundWindow();
        _lastLocaleId = KeyboardLayoutNative.GetActiveLocaleId();
        _pollTimer.Start();
    }

    public void Stop() => _pollTimer.Stop();

    public void SwitchToNext() => KeyboardLayoutNative.RequestNextLayout();

    public void Dispose()
    {
        _pollTimer.Stop();
        _pollTimer.Tick -= OnTick;
    }

    private void OnTick(object? sender, EventArgs e)
    {
        IntPtr foreground = KeyboardLayoutNative.GetForegroundWindow();
        if (foreground == IntPtr.Zero)
        {
            return;
        }

        bool appSwitched = foreground != _lastForegroundWindow;
        _lastForegroundWindow = foreground;

        int localeId = KeyboardLayoutNative.GetActiveLocaleId();
        if (localeId == _lastLocaleId)
        {
            return;
        }

        _lastLocaleId = localeId;

        // Moving to another application with a layout of its own is not the same as
        // the user switching the layout, and the subscribers are free to react to
        // these cases differently
        LayoutChangeReason reason = appSwitched
            ? LayoutChangeReason.ApplicationSwitched
            : LayoutChangeReason.UserSwitched;

        LayoutChanged?.Invoke(this, new LayoutChangedEventArgs(KeyboardLayout.FromLocaleId(localeId), reason));
    }
}