using System;
using AcDream.UI.Abstractions.Input;
using Silk.NET.Input;

namespace AcDream.App.Input;

/// <summary>
/// Bridges a Silk.NET <see cref="IMouse"/> + the active ImGui IO
/// (for <see cref="WantCaptureMouse"/> / <see cref="WantCaptureKeyboard"/>)
/// to the test-fakeable <see cref="IMouseSource"/> used by
/// <see cref="InputDispatcher"/>.
///
/// <para>
/// We don't link Hexa.NET.ImGui or ImGuiNET directly here — the
/// constructor takes two delegates so the App.Rendering layer can
/// proxy <c>ImGui.GetIO().WantCaptureMouse</c> via whichever ImGui
/// package is currently active without leaking the type onto the
/// abstraction interface.
/// </para>
/// </summary>
public sealed class SilkMouseSource : IMouseSource
{
    private readonly IMouse _mouse;
    private readonly Func<bool> _wantCaptureMouse;
    private readonly Func<bool> _wantCaptureKeyboard;
    private float _lastX;
    private float _lastY;
    private bool _haveLastPos;

    public event Action<MouseButton, ModifierMask>? MouseDown;
    public event Action<MouseButton, ModifierMask>? MouseUp;
    public event Action<float, float>? MouseMove;
    public event Action<float>? Scroll;

    /// <summary>Caller-supplied probe for the current modifier mask. Reused
    /// from the keyboard source so mouse events carry consistent modifier
    /// state.</summary>
    public Func<ModifierMask> ModifierProbe { get; set; } = () => ModifierMask.None;

    public SilkMouseSource(
        IMouse mouse,
        Func<bool> wantCaptureMouse,
        Func<bool> wantCaptureKeyboard)
    {
        _mouse = mouse ?? throw new ArgumentNullException(nameof(mouse));
        _wantCaptureMouse = wantCaptureMouse ?? throw new ArgumentNullException(nameof(wantCaptureMouse));
        _wantCaptureKeyboard = wantCaptureKeyboard ?? throw new ArgumentNullException(nameof(wantCaptureKeyboard));

        _mouse.MouseDown += (_, btn) => MouseDown?.Invoke(btn, ModifierProbe());
        _mouse.MouseUp   += (_, btn) => MouseUp?.Invoke(btn, ModifierProbe());
        _mouse.MouseMove += (_, pos) =>
        {
            float dx, dy;
            if (_haveLastPos)
            {
                dx = pos.X - _lastX;
                dy = pos.Y - _lastY;
            }
            else
            {
                dx = 0f;
                dy = 0f;
                _haveLastPos = true;
            }
            _lastX = pos.X;
            _lastY = pos.Y;
            MouseMove?.Invoke(dx, dy);
        };
        _mouse.Scroll += (_, scroll) => Scroll?.Invoke(scroll.Y);
    }

    public bool IsHeld(MouseButton button) => _mouse.IsButtonPressed(button);

    public bool WantCaptureMouse => _wantCaptureMouse();
    public bool WantCaptureKeyboard => _wantCaptureKeyboard();
}