using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Graphics;

using Syntriax.Engine.Core;

namespace Syntriax.Engine.Integration.MonoGame;

public class TriangleBatch : ITriangleBatch
{
    private readonly GraphicsDevice graphicsDevice;
    private VertexBuffer vertexBuffer = default!;
    private readonly VertexPositionColor[] vertices = new VertexPositionColor[1024];
    private int verticesIndex = 0;
    private Matrix _view;
    private Matrix _projection;
    private readonly BasicEffect basicEffect;

    public TriangleBatch(GraphicsDevice graphicsDevice)
    {
        this.graphicsDevice = graphicsDevice;
        this.graphicsDevice.RasterizerState = new RasterizerState() { CullMode = CullMode.None };
        basicEffect = new(graphicsDevice);
        basicEffect.VertexColorEnabled = true;
    }

    public void Draw(Triangle triangle, ColorRGBA colorRGBA)
    {
        if (verticesIndex + 3 >= vertices.Length)
            Flush();

        Vector2 A = triangle.A.ToDisplayVector2();
        Vector2 B = triangle.B.ToDisplayVector2();
        Vector2 C = triangle.C.ToDisplayVector2();
        Color color = colorRGBA.ToColor();

        vertices[verticesIndex++] = new(new(A.X, A.Y, 0f), color);
        vertices[verticesIndex++] = new(new(B.X, B.Y, 0f), color);
        vertices[verticesIndex++] = new(new(C.X, C.Y, 0f), color);
    }

    public void Begin(Matrix? view = null, Matrix? projection = null)
    {
        if (view != null)
            _view = view.Value;
        else
            _view = Matrix.Identity;

        if (projection != null)
            _projection = projection.Value;
        else
        {
            Viewport viewport = graphicsDevice.Viewport;
            _projection = Matrix.CreateOrthographicOffCenter(viewport.X, viewport.Width, viewport.Height, viewport.Y, 0, 1);
        }
    }

    public void End() => Flush();

    private void Flush()
    {
        basicEffect.Projection = _projection;
        basicEffect.View = _view;
        vertexBuffer = new VertexBuffer(graphicsDevice, typeof(VertexPositionColor), 1024, BufferUsage.WriteOnly);
        vertexBuffer.SetData(vertices);

        graphicsDevice.SetVertexBuffer(vertexBuffer);

        foreach (EffectPass pass in basicEffect.CurrentTechnique.Passes)
            pass.Apply();
        graphicsDevice.DrawPrimitives(PrimitiveType.TriangleList, 0, verticesIndex / 3);

        verticesIndex = 0;
    }
}