acdream/tests/AcDream.Core.Tests/Physics/CellTransitCheckBuildingTransitTests.cs

using System.Collections.Generic;
using System.Numerics;
using AcDream.Core.Physics;
using Xunit;

namespace AcDream.Core.Tests.Physics;

public class CellTransitCheckBuildingTransitTests
{
    [Fact]
    public void BuildingPortalWithUnloadedCellBSP_NoCandidateAdded()
    {
        // Verifies the null-CellBSP guard: when the destination interior cell
        // is cached but its CellBSP isn't yet loaded (or is structurally absent),
        // CheckBuildingTransit must NOT add the cell to candidates — even though
        // PointInsideCellBsp(null, _) returns true.
        //
        // Happy-path (CellBSP present, sphere inside) requires a synthetic
        // CellBSPTree which is non-trivial to construct from DatReaderWriter
        // types. Deferred to visual verification.

        // Building at world origin. One portal to interior cell 0xA9B40100.
        var building = new BuildingPhysics
        {
            WorldTransform = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            Portals = new[]
            {
                new BldPortalInfo(
                    otherCellId: 0xA9B40100u,
                    otherPortalId: 0,
                    flags: 0),
            },
        };

        // Interior cell with null CellBSP — PointInsideCellBsp(null, _) returns true,
        // but CheckBuildingTransit guards on CellBSP?.Root being non-null, so this
        // cell is skipped.
        var interiorCell = new CellPhysics
        {
            WorldTransform = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            Resolved = new Dictionary<ushort, ResolvedPolygon>(),
        };

        var cache = new PhysicsDataCache();
        cache.RegisterCellStructForTest(0xA9B40100u, interiorCell);

        var candidates = new HashSet<uint>();
        CellTransit.CheckBuildingTransit(
            cache, building,
            worldSphereCenter: new Vector3(0, 0, 0),
            sphereRadius: 0.5f,
            candidates);

        // CellBSP is null → containment guard (otherCell?.CellBSP?.Root is null)
        // skips this cell. No candidate added.
        Assert.Empty(candidates);
    }

    /// <summary>
    /// BR-7 / A6.P4 C1 (2026-06-11): retail's first gate in
    /// <c>CEnvCell::check_building_transit</c> (Ghidra 0x0052c5dc) is
    /// <c>if (other_portal_id &gt;= 0)</c> on the SIGNED sign-extended
    /// portal id — a portal whose dat value is 0xFFFF (-1, "no reciprocal
    /// portal") never admits its interior cell, even when a sphere
    /// overlaps it. A leaf-root CellBSP makes the sphere test
    /// unconditionally "inside", so the only thing separating the two
    /// portals below is the sign of OtherPortalId.
    /// </summary>
    [Fact]
    public void NegativeOtherPortalId_RejectsTransit_PositiveAdmits()
    {
        var leafBsp = new DatReaderWriter.Types.CellBSPTree
        {
            Root = new DatReaderWriter.Types.CellBSPNode
            {
                Type = DatReaderWriter.Enums.BSPNodeType.Leaf,
            },
        };

        CellPhysics MakeLeafCell() => new CellPhysics
        {
            WorldTransform = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            Resolved = new Dictionary<ushort, ResolvedPolygon>(),
            CellBSP = leafBsp,
        };

        var cache = new PhysicsDataCache();
        cache.RegisterCellStructForTest(0xA9B40101u, MakeLeafCell());
        cache.RegisterCellStructForTest(0xA9B40102u, MakeLeafCell());

        var building = new BuildingPhysics
        {
            WorldTransform = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            Portals = new[]
            {
                // Wire 0xFFFF reinterpreted signed = -1 → must be skipped.
                new BldPortalInfo(
                    otherCellId: 0xA9B40101u,
                    otherPortalId: unchecked((short)0xFFFF),
                    flags: 0),
                // Non-negative id → admitted (leaf BSP ⇒ sphere inside).
                new BldPortalInfo(
                    otherCellId: 0xA9B40102u,
                    otherPortalId: 0,
                    flags: 0),
            },
        };

        var candidates = new HashSet<uint>();
        CellTransit.CheckBuildingTransit(
            cache, building,
            worldSphereCenter: new Vector3(0, 0, 0),
            sphereRadius: 0.5f,
            candidates);

        Assert.DoesNotContain(0xA9B40101u, candidates);
        Assert.Contains(0xA9B40102u, candidates);
    }

    /// <summary>
    /// Multi-sphere form (retail per-sphere loop at 0052c5fe): the first
    /// intersecting sphere admits the cell and sets
    /// <c>hitsInteriorCell</c> (retail SPHEREPATH.hits_interior_cell write
    /// at 0052c650). All-spheres-outside ⇒ no admit, flag false.
    /// </summary>
    [Fact]
    public void MultiSphere_AnySphereAdmits_SetsHitsInteriorCell()
    {
        var leafBsp = new DatReaderWriter.Types.CellBSPTree
        {
            Root = new DatReaderWriter.Types.CellBSPNode
            {
                Type = DatReaderWriter.Enums.BSPNodeType.Leaf,
            },
        };
        var cache = new PhysicsDataCache();
        cache.RegisterCellStructForTest(0xA9B40103u, new CellPhysics
        {
            WorldTransform = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            Resolved = new Dictionary<ushort, ResolvedPolygon>(),
            CellBSP = leafBsp,
        });

        var building = new BuildingPhysics
        {
            WorldTransform = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            Portals = new[]
            {
                new BldPortalInfo(0xA9B40103u, otherPortalId: 1, flags: 0),
            },
        };

        var spheres = new[]
        {
            new DatReaderWriter.Types.Sphere { Origin = new Vector3(500f, 0f, 0f), Radius = 0.5f },
            new DatReaderWriter.Types.Sphere { Origin = Vector3.Zero,              Radius = 0.5f },
        };

        var candidates = new HashSet<uint>();
        CellTransit.CheckBuildingTransit(
            cache, building, spheres, spheres.Length, candidates, out bool hits);

        // Leaf-root BSP treats every sphere as inside, so even the far
        // sphere admits; the point of this test is the plumbing: candidates
        // populated + hitsInteriorCell set through the multi-sphere form.
        Assert.Contains(0xA9B40103u, candidates);
        Assert.True(hits);

        // Zero spheres → nothing admitted, flag stays false.
        var empty = new HashSet<uint>();
        CellTransit.CheckBuildingTransit(
            cache, building, spheres, 0, empty, out bool hitsNone);
        Assert.Empty(empty);
        Assert.False(hitsNone);
    }
}