using System.Collections.Generic;
using System.Linq;

using Engine.Core;
using Engine.Physics2D;
using Engine.Systems.Graphics;
using Engine.Systems.Tween;

namespace Pong.Behaviours;

public class BallTrail : Behaviour2D, IPostPhysicsUpdate, IDrawableTriangle
{
    private float width = 10f;
    private IEasing widthCurve = EaseInCirc.Instance;

    private ColorRGBA colorBase = new ColorRGBA(255, 255, 255, 255);
    private ColorRGBA colorEnd = new ColorRGBA(255, 255, 255, 0);
    private IEasing colorEasing = EaseOutSine.Instance;

    private int trailTickPeriod = 20;

    private readonly LinkedList<Vector2D> trailPoints = new();

    public void PostPhysicsUpdate(float delta)
    {
        trailPoints.AddFirst(Transform.Position);
        if (trailPoints.Count > trailTickPeriod)
            trailPoints.RemoveLast();
    }

    public void Draw(ITriangleBatch triangleBatch)
    {
        for (int i = 0; i < trailPoints.Count - 2; i++)
        {
            Line2D line = new(trailPoints.ElementAt(i), trailPoints.ElementAt(i + 1));
            Vector2D perpendicularDirection = line.Direction.Perpendicular();

            float t = (float)i / trailPoints.Count;
            float tPlus = (float)(i + 1) / trailPoints.Count;

            float firstWidth = width * widthCurve.Evaluate(1f - t);
            float endWidth = width * widthCurve.Evaluate(1f - tPlus);

            ColorRGBA color = colorBase.Lerp(colorEnd, colorEasing.Evaluate(t));

            triangleBatch.Draw(
                new(line.From + perpendicularDirection * firstWidth,
                    line.From - perpendicularDirection * firstWidth,
                    line.To + perpendicularDirection * endWidth),
                color
            );

            triangleBatch.Draw(
                new(line.From - perpendicularDirection * firstWidth,
                    line.To - perpendicularDirection * endWidth,
                    line.To + perpendicularDirection * endWidth),
                color
            );
        }
    }
}