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

namespace AcDream.Core.Tests.Physics;

public class CellTransitFindTransitCellsSphereTests
{
    private static CellBSPTree SinglePlaneCellBsp()
    {
        var leaf = new CellBSPNode { Type = DatReaderWriter.Enums.BSPNodeType.Leaf };
        return new CellBSPTree
        {
            Root = new CellBSPNode
            {
                // Local x >= 0 is inside this synthetic cell.
                SplittingPlane = new Plane(new Vector3(1f, 0f, 0f), 0f),
                PosNode = leaf,
            }
        };
    }

    private static CellPhysics MakeCellWithPortalAtRightWall(
        Matrix4x4 worldTransform, uint otherCellId, ushort flags)
    {
        // Portal poly at local x=2.5 (right wall), normal +X.
        var portalPolyA = new ResolvedPolygon
        {
            Vertices  = new[]
            {
                new Vector3(2.5f, -2.5f,  0f),
                new Vector3(2.5f,  2.5f,  0f),
                new Vector3(2.5f,  2.5f,  5f),
                new Vector3(2.5f, -2.5f,  5f),
            },
            Plane     = new Plane(new Vector3(1, 0, 0), -2.5f),  // x = 2.5
            NumPoints = 4,
            SidesType = DatReaderWriter.Enums.CullMode.None,
        };

        Matrix4x4.Invert(worldTransform, out var inv);
        return new CellPhysics
        {
            WorldTransform = worldTransform,
            InverseWorldTransform = inv,
            Resolved = new Dictionary<ushort, ResolvedPolygon>(),
            PortalPolygons = new Dictionary<ushort, ResolvedPolygon> { [10] = portalPolyA },
            Portals = new[]
            {
                new PortalInfo(otherCellId: (ushort)otherCellId, polygonId: 10, flags: flags),
            },
        };
    }

    [Fact]
    public void SphereInsideCellA_NearPortal_AddsCellB()
    {
        var cellA = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherCellId: 0x0101, flags: 0);

        var cellBT = Matrix4x4.CreateTranslation(new Vector3(5f, 0f, 0f));
        Matrix4x4.Invert(cellBT, out var cellBInv);
        var cellB = new CellPhysics
        {
            WorldTransform = cellBT,
            InverseWorldTransform = cellBInv,
            Resolved = new Dictionary<ushort, ResolvedPolygon>(),
        };

        var cache = new PhysicsDataCache();
        cache.RegisterCellStructForTest(0xA9B40100u, cellA);
        cache.RegisterCellStructForTest(0xA9B40101u, cellB);

        // Sphere center near portal (local x=2.0, radius=0.5 → reaches x=2.5 = portal plane).
        var worldSphereCenter = new Vector3(2.0f, 0f, 2.5f);

        var candidates = new HashSet<uint>();
        CellTransit.FindTransitCellsSphere(
            cache, cellA, currentCellId: 0xA9B40100u,
            worldSphereCenter, sphereRadius: 0.5f, candidates, out bool exitOutside);

        Assert.Contains(0xA9B40101u, candidates);
        Assert.False(exitOutside);
    }

    [Fact]
    public void SphereInsideCellA_FarFromPortal_DoesNotAddCellB()
    {
        var cellA = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherCellId: 0x0101, flags: 0);

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

        // Sphere far from portal (local x=-1.0, reach to x=-0.5 — nowhere near portal at x=2.5).
        var worldSphereCenter = new Vector3(-1.0f, 0f, 2.5f);

        var candidates = new HashSet<uint>();
        CellTransit.FindTransitCellsSphere(
            cache, cellA, currentCellId: 0xA9B40100u,
            worldSphereCenter, sphereRadius: 0.5f, candidates, out bool exitOutside);

        Assert.DoesNotContain(0xA9B40101u, candidates);
    }

    [Fact]
    public void LoadedNeighbor_SphereIntersectsNeighborCellBsp_AddsEvenWhenPortalHintWouldReject()
    {
        // Retail CEnvCell::find_transit_cells uses the loaded neighbour's
        // CellBSP sphere-overlap test. The portal-plane side test is only
        // an unloaded-cell hint. flags=2 makes the old heuristic reject
        // this world position even though the sphere overlaps cell B.
        var cellA = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherCellId: 0x0101, flags: 2);

        var cellBT = Matrix4x4.CreateTranslation(new Vector3(5f, 0f, 0f));
        Matrix4x4.Invert(cellBT, out var cellBInv);
        var cellB = new CellPhysics
        {
            WorldTransform        = cellBT,
            InverseWorldTransform = cellBInv,
            Resolved              = new Dictionary<ushort, ResolvedPolygon>(),
            CellBSP               = SinglePlaneCellBsp(),
        };

        var cache = new PhysicsDataCache();
        cache.RegisterCellStructForTest(0xA9B40100u, cellA);
        cache.RegisterCellStructForTest(0xA9B40101u, cellB);

        // Cell B local center is x=-0.25, radius=0.5, so the sphere
        // straddles x=0 and intersects the cell volume.
        var worldSphereCenter = new Vector3(4.75f, 0f, 2.5f);

        var candidates = new HashSet<uint>();
        CellTransit.FindTransitCellsSphere(
            cache, cellA, currentCellId: 0xA9B40100u,
            worldSphereCenter, sphereRadius: 0.5f, candidates, out bool exitOutside);

        Assert.Contains(0xA9B40101u, candidates);
        Assert.False(exitOutside);
    }

    [Fact]
    public void LoadedNeighbor_SphereOutsideNeighborCellBsp_DoesNotUsePortalHintFallback()
    {
        // With a loaded neighbour, retail trusts sphere_intersects_cell.
        // This guards against adding the neighbour merely because the
        // current-cell portal plane would have accepted the sphere.
        var cellA = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherCellId: 0x0101, flags: 0);

        var cellBT = Matrix4x4.CreateTranslation(new Vector3(5f, 0f, 0f));
        Matrix4x4.Invert(cellBT, out var cellBInv);
        var cellB = new CellPhysics
        {
            WorldTransform        = cellBT,
            InverseWorldTransform = cellBInv,
            Resolved              = new Dictionary<ushort, ResolvedPolygon>(),
            CellBSP               = SinglePlaneCellBsp(),
        };

        var cache = new PhysicsDataCache();
        cache.RegisterCellStructForTest(0xA9B40100u, cellA);
        cache.RegisterCellStructForTest(0xA9B40101u, cellB);

        // Current portal-plane heuristic would add this (near x=2.5), but
        // in cell B local space x=-1.95 with radius=0.5 is fully outside.
        var worldSphereCenter = new Vector3(3.05f, 0f, 2.5f);

        var candidates = new HashSet<uint>();
        CellTransit.FindTransitCellsSphere(
            cache, cellA, currentCellId: 0xA9B40100u,
            worldSphereCenter, sphereRadius: 0.5f, candidates, out bool exitOutside);

        Assert.DoesNotContain(0xA9B40101u, candidates);
        Assert.False(exitOutside);
    }

    [Fact]
    public void ExitPortal_SphereStraddlesPortalPlane_FlagsCheckOutside()
    {
        var exitCell = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherCellId: 0xFFFF, flags: 0);

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

        var worldSphereCenter = new Vector3(2.0f, 0f, 2.5f);
        var candidates = new HashSet<uint>();

        CellTransit.FindTransitCellsSphere(
            cache, exitCell, currentCellId: 0xA9B40100u,
            worldSphereCenter, sphereRadius: 0.5f, candidates, out bool exitOutside);

        Assert.True(exitOutside);
    }

    [Fact]
    public void ExitPortal_SecondSphereStraddlesPortalPlane_FlagsCheckOutside()
    {
        // Retail passes the whole SPHEREPATH global_sphere array into
        // CEnvCell::find_transit_cells. The head sphere can be the one that
        // overlaps an exit portal while the foot sphere is still clear.
        var exitCell = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherCellId: 0xFFFF, flags: 0);

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

        var spheres = new[]
        {
            new Sphere { Origin = new Vector3(0.0f, 0f, 2.5f), Radius = 0.5f },
            new Sphere { Origin = new Vector3(2.0f, 0f, 3.2f), Radius = 0.5f },
        };
        var candidates = new HashSet<uint>();

        CellTransit.FindTransitCellsSphere(
            cache, exitCell, currentCellId: 0xA9B40100u,
            spheres, spheres.Length, candidates, out bool exitOutside);

        Assert.True(exitOutside);
    }
}