using System;
using System.Numerics;
using AcDream.Core.Selection;
using Xunit;

namespace AcDream.Core.Tests.Selection;

public class WorldPickerTests
{
    private const float Epsilon = 0.01f;

    private static (Matrix4x4 View, Matrix4x4 Projection) MakeIdentityCamera()
    {
        var view = Matrix4x4.Identity;
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(
            fieldOfView: MathF.PI / 3f,
            aspectRatio: 16f / 9f,
            nearPlaneDistance: 0.1f,
            farPlaneDistance: 100f);
        return (view, proj);
    }

    [Fact]
    public void BuildRay_CenterOfViewport_ReturnsForwardRay()
    {
        var (view, proj) = MakeIdentityCamera();
        const float vpW = 1920f, vpH = 1080f;

        var (_, direction) = WorldPicker.BuildRay(
            mouseX: vpW / 2f, mouseY: vpH / 2f,
            viewportW: vpW, viewportH: vpH,
            view, proj);

        // Right-handed perspective + identity view -> camera looks down -Z.
        // Center pixel ray = (0, 0, -1) within float epsilon.
        Assert.True(MathF.Abs(direction.X) < Epsilon, $"direction.X = {direction.X}");
        Assert.True(MathF.Abs(direction.Y) < Epsilon, $"direction.Y = {direction.Y}");
        Assert.True(direction.Z < -0.99f,             $"direction.Z = {direction.Z}");
    }

    [Fact]
    public void BuildRay_OffsetMouseRight_DeflectsRayPositiveX()
    {
        var (view, proj) = MakeIdentityCamera();
        const float vpW = 1920f, vpH = 1080f;

        var (_, direction) = WorldPicker.BuildRay(
            mouseX: vpW * 0.75f, mouseY: vpH / 2f,
            viewportW: vpW, viewportH: vpH,
            view, proj);

        Assert.True(direction.X > 0.1f, $"direction.X = {direction.X} (expected > 0.1)");
    }
}