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

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.
/// </summary>
public sealed class UiRenderSystem : BaseSystem
{
    private readonly Desktop _desktop;

    /// <summary>Creates the system for <paramref name="desktop"/>.</summary>
    public UiRenderSystem(Desktop desktop) => _desktop = desktop;

    /// <inheritdoc />
    protected override void OnUpdateGroup() => _desktop.Render();
}

/// <summary>Wires the UI module (Myra) into a <see cref="Scene"/>.</summary>
public static class SceneUiExtensions
{
    private static bool _environmentInitialized;

    /// <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"/>.
    /// </summary>
    public static Desktop UseUI(this Scene scene)
    {
        // Геттер MyraEnvironment.Game бросает исключение, пока Game не задан — проверять через ??= нельзя.
        if (!_environmentInitialized)
        {
            MyraEnvironment.Game = scene.Context.Services.Get<Game>();
            _environmentInitialized = true;
        }

        var desktop = new Desktop();
        scene.DrawSystems.Add(new UiRenderSystem(desktop));
        return desktop;
    }
}