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

namespace AcDream.App.Tests.Rendering;

public class PortalVisibilityBuilderTests
{
    private static Matrix4x4 ViewProj()
    {
        var view = Matrix4x4.CreateLookAt(Vector3.Zero, new Vector3(0, 0, -1), Vector3.UnitY);
        var proj = Matrix4x4.CreatePerspectiveFieldOfView(1.2f, 1.0f, 0.1f, 1000f);
        return view * proj;
    }

    private static Vector3[] Quad(float cx, float cy, float halfW, float halfH, float z) => new[]
    {
        new Vector3(cx - halfW, cy - halfH, z), new Vector3(cx + halfW, cy - halfH, z),
        new Vector3(cx + halfW, cy + halfH, z), new Vector3(cx - halfW, cy + halfH, z),
    };

    private static LoadedCell Cell(uint id, params CellPortalInfo[] portals) => new LoadedCell
    {
        CellId = id, WorldTransform = Matrix4x4.Identity, InverseWorldTransform = Matrix4x4.Identity,
        Portals = new List<CellPortalInfo>(portals),
    };

    private static PortalVisibilityFrame Build(LoadedCell cam, Dictionary<uint, LoadedCell> all)
        => PortalVisibilityBuilder.Build(cam, Vector3.Zero, id => all.TryGetValue(id, out var c) ? c : null, ViewProj());

    [Fact]
    public void Builder_Cellar_WindowClippedToStairwell_NotFullWindow()
    {
        var cam = Cell(0x0001, new CellPortalInfo(0x0002, 0, 0));
        cam.PortalPolygons.Add(Quad(0f, 0f, 0.1f, 1.0f, -3f)); // narrow stairwell
        var ground = Cell(0x0002, new CellPortalInfo(0xFFFF, 0, 0));
        ground.PortalPolygons.Add(Quad(0f, 0f, 1.0f, 1.0f, -6f)); // wide window
        var all = new Dictionary<uint, LoadedCell> { [0x0001] = cam, [0x0002] = ground };

        var frame = Build(cam, all);

        Assert.False(frame.OutsideView.IsEmpty);
        float outsideWidth = frame.OutsideView.MaxX - frame.OutsideView.MinX;
        float windowOnlyWidth = PortalFrameTestHelper.ProjectedWidth(
            new[] { new Vector3(-1, 0, -6), new Vector3(1, 0, -6) }, ViewProj());
        Assert.True(outsideWidth < windowOnlyWidth * 0.5f,
            $"OutsideView width {outsideWidth} should be a sliver, far less than full window {windowOnlyWidth}");
    }

    [Fact]
    public void Builder_SealedCellar_NoExitPortal_OutsideViewEmpty()
    {
        var cam = Cell(0x0001, new CellPortalInfo(0x0002, 0, 0));
        cam.PortalPolygons.Add(Quad(0, 0, 0.1f, 1f, -3f));
        var inner = Cell(0x0002); // no portals at all
        var all = new Dictionary<uint, LoadedCell> { [0x0001] = cam, [0x0002] = inner };
        Assert.True(Build(cam, all).OutsideView.IsEmpty);
    }

    [Fact]
    public void Builder_CameraCellWithDirectExit_OutsideViewIsFullWindow()
    {
        var cam = Cell(0x0001, new CellPortalInfo(0xFFFF, 0, 0));
        cam.PortalPolygons.Add(Quad(0, 0, 1f, 1f, -6f));
        var all = new Dictionary<uint, LoadedCell> { [0x0001] = cam };
        var frame = Build(cam, all);
        Assert.False(frame.OutsideView.IsEmpty);
        Assert.True(frame.OutsideView.MaxX - frame.OutsideView.MinX > 0.3f);
    }

    [Fact]
    public void Builder_BackFacingPortal_NotTraversed()
    {
        // Portal to 0x0002, but its clip plane puts the camera (origin) on the OUTSIDE.
        var cam = Cell(0x0001, new CellPortalInfo(0x0002, 0, 0));
        cam.PortalPolygons.Add(Quad(0, 0, 0.5f, 0.5f, -3f));
        cam.ClipPlanes.Add(new PortalClipPlane { Normal = new Vector3(0, 0, 1), D = -1f, InsideSide = 0 });
        // dot = (0,0,1)·origin + (-1) = -1 < 0; InsideSide==0 requires dot >= -eps → camera OUTSIDE → skip.
        var ground = Cell(0x0002, new CellPortalInfo(0xFFFF, 0, 0));
        ground.PortalPolygons.Add(Quad(0, 0, 1f, 1f, -6f));
        var all = new Dictionary<uint, LoadedCell> { [0x0001] = cam, [0x0002] = ground };

        var frame = Build(cam, all);
        Assert.False(frame.CellViews.ContainsKey(0x0002)); // neighbour never reached
        Assert.True(frame.OutsideView.IsEmpty);            // its window never marked
    }

    [Fact]
    public void Builder_CwWoundExitPortal_OutsideRegionIsCcw()
    {
        // Exit portal authored CLOCKWISE — the builder must normalize to CCW so downstream stays valid.
        var cwQuad = new[]
        {
            new Vector3(-1, -1, -6), new Vector3(-1, 1, -6), new Vector3(1, 1, -6), new Vector3(1, -1, -6),
        };
        var cam = Cell(0x0001, new CellPortalInfo(0xFFFF, 0, 0));
        cam.PortalPolygons.Add(cwQuad);
        var all = new Dictionary<uint, LoadedCell> { [0x0001] = cam };
        var frame = Build(cam, all);
        Assert.False(frame.OutsideView.IsEmpty);
        var p = frame.OutsideView.Polygons[0].Vertices;
        float area2 = 0f;
        for (int i = 0; i < p.Length; i++) { var a = p[i]; var b = p[(i + 1) % p.Length]; area2 += a.X * b.Y - b.X * a.Y; }
        Assert.True(area2 > 0f, "clipped OutsideView region should be CCW after winding normalization");
    }

    [Fact]
    public void Builder_CyclicGraph_TerminatesWithBoundedPolys()
    {
        // A <-> B cycle; B also has an exit window. Must terminate and not blow up.
        var a = Cell(0x0001, new CellPortalInfo(0x0002, 0, 0));
        a.PortalPolygons.Add(Quad(0f, 0f, 0.5f, 0.5f, -3f));
        var b = Cell(0x0002, new CellPortalInfo(0x0001, 0, 0), new CellPortalInfo(0xFFFF, 1, 0));
        b.PortalPolygons.Add(Quad(0f, 0f, 0.5f, 0.5f, -2f)); // back to A
        b.PortalPolygons.Add(Quad(0f, 0f, 1.0f, 1.0f, -6f)); // exit window
        var all = new Dictionary<uint, LoadedCell> { [0x0001] = a, [0x0002] = b };

        var frame = Build(a, all); // must return (no infinite loop)
        Assert.False(frame.OutsideView.IsEmpty);
        Assert.True(frame.OutsideView.Polygons.Count < 256,
            $"OutsideView poly count {frame.OutsideView.Polygons.Count} — termination/dedup regression guard");
    }
}

internal static class PortalFrameTestHelper
{
    public static float ProjectedWidth(Vector3[] worldSeg, Matrix4x4 vp)
    {
        var a = Vector4.Transform(new Vector4(worldSeg[0], 1f), vp);
        var b = Vector4.Transform(new Vector4(worldSeg[1], 1f), vp);
        return System.MathF.Abs(a.X / a.W - b.X / b.W);
    }
}