using System.Collections.Generic;

using Engine.Core;

namespace Engine.Systems.Graphics;

public class TriangleBatcher : Behaviour, IFirstFrameUpdate, IDraw
{
    private static Comparer<int> SortByAscendingPriority() => Comparer<int>.Create((x, y) => x.CompareTo(y));
    private static System.Func<IBehaviour, int> GetPriority() => (b) => b.Priority;

    private ITriangleBatch triangleBatch = null!;
    private ICamera camera = null!;

    private readonly ActiveBehaviourCollectorOrdered<int, IDrawableTriangle> drawableShapes = new(GetPriority(), SortByAscendingPriority());

    public void FirstActiveFrame()
    {
        camera = Universe.FindRequiredBehaviour<ICamera>();

        triangleBatch = Universe.FindRequiredBehaviour<ITriangleBatch>();
        drawableShapes.Unassign();
        drawableShapes.Assign(Universe);
    }

    public void Draw()
    {
        triangleBatch.Begin(camera.ViewMatrix, camera.ProjectionMatrix);
        for (int i = 0; i < drawableShapes.Count; i++)
            drawableShapes[i].Draw(triangleBatch);
        triangleBatch.End();
    }
}