using Friflo.Engine.ECS.Systems;
using Microsoft.Xna.Framework;
using MrGameEng.Core;
using Myra;
using Myra.Graphics2D.UI;

namespace MrGameEng.UI;

/// <summary>
/// Draw system rendering the scene's Myra <see cref="Desktop"/>. Must run after the scene's
/// world rendering (register UI last in the draw phase) — the UI is drawn on top in window
/// pixels and also processes mouse/keyboard interaction during render. While
/// <see cref="InputCapture.Captured"/> is set (developer console open), the desktop is drawn
/// without processing input, so overlay clicks and keystrokes do not fall through to it.
/// </summary>
public sealed class UiRenderSystem : BaseSystem
{
    private readonly Desktop _desktop;
    private readonly InputCapture? _capture;

    /// <summary>Creates the system for <paramref name="desktop"/>.</summary>
    public UiRenderSystem(Desktop desktop, InputCapture? capture = null)
    {
        _desktop = desktop;
        _capture = capture;
    }

    /// <inheritdoc />
    protected override void OnUpdateGroup()
    {
        if (_capture?.Captured == true)
        {
            // Render() = UpdateInput + UpdateLayout + RenderVisual; пропускаем только ввод.
            _desktop.UpdateLayout();
            _desktop.RenderVisual();
        }
        else
        {
            _desktop.Render();
        }
    }
}

/// <summary>Wires the UI module (Myra) into a <see cref="Scene"/>.</summary>
public static class SceneUiExtensions
{
    /// <summary>
    /// Creates a Myra <see cref="Desktop"/> for this scene and registers
    /// <see cref="UiRenderSystem"/> in the draw phase. Call from <c>OnLoad</c>
    /// <b>after</b> <c>UseRenderer2D()</c> so the UI draws on top of the world.
    /// Build the UI by assigning <see cref="Desktop.Root"/>. The desktop is disposed
    /// automatically when the scene unloads.
    /// </summary>
    public static Desktop UseUI(this Scene scene)
    {
        var services = scene.Context.Services;

        // Присваивание идемпотентно; геттер MyraEnvironment.Game бросает исключение, пока
        // Game не задан, поэтому проверять текущее значение перед записью нельзя.
        MyraEnvironment.Game = services.Get<Game>();

        var capture = services.GetOrDefault<InputCapture>();
        if (capture is null)
        {
            capture = new InputCapture();
            services.Add(capture);
        }

        var desktop = new Desktop();
        scene.RegisterUnload(desktop.Dispose);
        scene.DrawSystems.Add(new UiRenderSystem(desktop, capture));
        return desktop;
    }
}