using System.Numerics;
using AcDream.App.Rendering;
using Xunit;

namespace AcDream.Core.Tests.Rendering;

public class FrustumCullerTests
{
    [Fact]
    public void IdentityVP_EverythingVisible()
    {
        // Identity VP: all planes at infinity, every box is visible.
        // Actually identity VP has degenerate planes — instead use a
        // simple ortho that covers [-1,1]³.
        var vp = Matrix4x4.CreateOrthographic(2f, 2f, 0.1f, 100f);
        var planes = FrustumPlanes.FromViewProjection(vp);

        // Box at origin, well within the frustum.
        Assert.True(FrustumCuller.IsAabbVisible(planes,
            new Vector3(-0.5f, -0.5f, -50f),
            new Vector3(0.5f, 0.5f, -1f)));
    }

    [Fact]
    public void PerspectiveCamera_BoxInFront_Visible()
    {
        var view = Matrix4x4.CreateLookAt(
            new Vector3(0, 0, 0),
            new Vector3(0, 0, -1),
            Vector3.UnitY);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(
            MathF.PI / 3f, 1f, 1f, 1000f);
        var planes = FrustumPlanes.FromViewProjection(view * proj);

        // Box directly in front of the camera.
        Assert.True(FrustumCuller.IsAabbVisible(planes,
            new Vector3(-10f, -10f, -100f),
            new Vector3(10f, 10f, -10f)));
    }

    [Fact]
    public void PerspectiveCamera_BoxBehind_NotVisible()
    {
        var view = Matrix4x4.CreateLookAt(
            new Vector3(0, 0, 0),
            new Vector3(0, 0, -1),
            Vector3.UnitY);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(
            MathF.PI / 3f, 1f, 1f, 1000f);
        var planes = FrustumPlanes.FromViewProjection(view * proj);

        // Box entirely behind the camera (positive Z).
        Assert.False(FrustumCuller.IsAabbVisible(planes,
            new Vector3(-10f, -10f, 10f),
            new Vector3(10f, 10f, 100f)));
    }

    [Fact]
    public void PerspectiveCamera_BoxFarLeft_NotVisible()
    {
        var view = Matrix4x4.CreateLookAt(
            new Vector3(0, 0, 0),
            new Vector3(0, 0, -1),
            Vector3.UnitY);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(
            MathF.PI / 3f, 1f, 1f, 1000f);
        var planes = FrustumPlanes.FromViewProjection(view * proj);

        // Box way off to the left.
        Assert.False(FrustumCuller.IsAabbVisible(planes,
            new Vector3(-1000f, -10f, -50f),
            new Vector3(-500f, 10f, -10f)));
    }

    [Fact]
    public void PerspectiveCamera_BoxStraddlingNearPlane_Visible()
    {
        var view = Matrix4x4.CreateLookAt(
            new Vector3(0, 0, 0),
            new Vector3(0, 0, -1),
            Vector3.UnitY);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(
            MathF.PI / 3f, 1f, 1f, 1000f);
        var planes = FrustumPlanes.FromViewProjection(view * proj);

        // Box that straddles the near plane (conservative: visible).
        Assert.True(FrustumCuller.IsAabbVisible(planes,
            new Vector3(-1f, -1f, -2f),
            new Vector3(1f, 1f, 0.5f)));
    }

    [Fact]
    public void PerspectiveCamera_BoxBeyondFarPlane_NotVisible()
    {
        var view = Matrix4x4.CreateLookAt(
            new Vector3(0, 0, 0),
            new Vector3(0, 0, -1),
            Vector3.UnitY);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(
            MathF.PI / 3f, 1f, 1f, 100f);
        var planes = FrustumPlanes.FromViewProjection(view * proj);

        // Box far beyond the far plane.
        Assert.False(FrustumCuller.IsAabbVisible(planes,
            new Vector3(-10f, -10f, -500f),
            new Vector3(10f, 10f, -200f)));
    }

    [Fact]
    public void AcdreamCamera_LandblockInFront_Visible()
    {
        // Simulate acdream's actual camera setup (Z-up, looking +Y,
        // positioned at Holtburg). A landblock-sized AABB at the
        // camera's forward should be visible.
        var view = Matrix4x4.CreateLookAt(
            new Vector3(96f, 96f, 150f),    // camera pos (center of a landblock, elevated)
            new Vector3(96f, 288f, 100f),   // looking roughly +Y (forward toward next landblock)
            Vector3.UnitZ);                  // Z-up
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(
            MathF.PI / 3f, 16f / 9f, 1f, 5000f);
        var planes = FrustumPlanes.FromViewProjection(view * proj);

        // Landblock-sized AABB 192 units ahead in Y.
        Assert.True(FrustumCuller.IsAabbVisible(planes,
            new Vector3(0f, 192f, 50f),
            new Vector3(192f, 384f, 200f)));

        // Landblock behind the camera (negative Y relative to camera).
        Assert.False(FrustumCuller.IsAabbVisible(planes,
            new Vector3(0f, -384f, 50f),
            new Vector3(192f, -192f, 200f)));
    }
}