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

namespace AcDream.Core.Tests.Physics;

public class CellTransitFindCellSetTests
{
    // ──────────────────────────────────────────────────────────────────
    // Helpers — mirror CellTransitFindTransitCellsSphereTests.cs pattern
    // ──────────────────────────────────────────────────────────────────

    private static CellPhysics MakeCellWithPortalAtRightWall(
        Matrix4x4 worldTransform, uint otherCellId, ushort flags)
    {
        var portalPoly = 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 = 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] = portalPoly },
            Portals               = new[]
            {
                new PortalInfo(otherCellId: (ushort)otherCellId, polygonId: 10, flags: flags),
            },
            CellBSP = new CellBSPTree
            {
                Root = new CellBSPNode { Type = BSPNodeType.Leaf },
            }
        };
    }

    // ──────────────────────────────────────────────────────────────────
    // Tests
    // ──────────────────────────────────────────────────────────────────

    [Fact]
    public void Sphere_FullyInsidePrimaryCell_ReturnsOnlyPrimary()
    {
        var cellA = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherCellId: 0x0101, flags: 0);
        var cache = new PhysicsDataCache();
        cache.RegisterCellStructForTest(0xA9B40100u, cellA);

        // Sphere far from any portal — local x=-1, reach to x=-0.5; portal at x=2.5.
        var sphereCenter = new Vector3(-1.0f, 0f, 2.5f);

        uint containing = CellTransit.FindCellSet(
            cache, sphereCenter, sphereRadius: 0.5f,
            currentCellId: 0xA9B40100u,
            out var cellSet);

        Assert.Equal(0xA9B40100u, containing);
        Assert.Single(cellSet);
        Assert.Contains(0xA9B40100u, cellSet);
    }

    [Fact]
    public void Sphere_StraddlingPortal_ReturnsBothCells()
    {
        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 = new CellBSPTree
            {
                Root = new CellBSPNode { Type = BSPNodeType.Leaf },
            }
        };

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

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

        uint containing = CellTransit.FindCellSet(
            cache, sphereCenter, sphereRadius: 0.5f,
            currentCellId: 0xA9B40100u,
            out var cellSet);

        Assert.Contains(0xA9B40100u, cellSet);
        Assert.Contains(0xA9B40101u, cellSet);
    }

    [Fact]
    public void FindCellSet_OutdoorSeed_IncludesNeighbourLandcells()
    {
        var cache = new PhysicsDataCache();
        // A6.P4 (2026-05-24): sphere coords are LANDBLOCK-LOCAL (X/Y in
        // [0, 192]). Place the sphere center near the east boundary of
        // landcell grid(0,0) (i.e., near local X=24) so AddAllOutsideCells
        // adds the east neighbour grid(1,0).
        var sphereCenter = new Vector3(23.8f, 12f, 0f);

        uint containing = CellTransit.FindCellSet(
            cache, sphereCenter, sphereRadius: 0.5f,
            currentCellId: 0xA9B40001u,  // outdoor cell, low byte < 0x100
            out var cellSet);

        Assert.Equal(0xA9B40001u, containing);
        Assert.True(cellSet.Count >= 2, $"Expected ≥2 cells in set (primary + east neighbour), got {cellSet.Count}");
    }

    [Fact]
    public void IndoorSeed_ExitPortalTouchedOnlyBySecondSphere_AddsOutdoorLandcell()
    {
        // A6.P4 (2026-05-24): landblock-local sphere coords. Cell sits at
        // the landblock origin (identity transform), so cell-local == world.
        // Sphere head at local (2, 12, 3.2) reaches the cell's exit portal
        // plane at local X=2.5 → AddAllOutsideCells fires.
        var exitCell = MakeCellWithPortalAtRightWall(
            Matrix4x4.Identity,
            otherCellId: 0xFFFF,
            flags: 0);

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

        var spheres = new[]
        {
            // Foot sphere is not near the exit portal plane at local x=2.5.
            new Sphere { Origin = new Vector3(0f, 12f, 2.5f), Radius = 0.5f },
            // Head sphere reaches the exit portal plane and should trigger
            // outdoor landcell expansion.
            new Sphere { Origin = new Vector3(2f, 12f, 3.2f), Radius = 0.5f },
        };

        uint containing = CellTransit.FindCellSet(
            cache, spheres, spheres.Length,
            currentCellId: 0xA9B40100u,
            out var cellSet);

        Assert.Equal(0xA9B40100u, containing);
        Assert.Contains(0xA9B40100u, cellSet);
        Assert.Contains(0xA9B40001u, cellSet);
    }

    // ──────────────────────────────────────────────────────────────────
    // Membership hysteresis — the R1-flap root cause.
    // Retail CObjCell::find_cell_list adds the CURRENT cell at index 0
    // (add_cell, pc:308766) and the pick loop iterates from index 0 with
    // interior-wins-break (pc:308791-308819) — so when two cells' BSPs both
    // contain the sphere center at a boundary, the CURRENT cell wins and the
    // membership does NOT flip. acdream's unordered-HashSet pick dropped that
    // ordering, producing the stair/room/doorway ping-pong (cell flips every
    // tick while straddling). This guards the current-cell-first behaviour.
    // ──────────────────────────────────────────────────────────────────

    [Theory]
    [InlineData(0xA9B40100u, 0xA9B40101u)]
    [InlineData(0xA9B40101u, 0xA9B40100u)]
    public void TwoOverlappingCells_CurrentCellWinsTheStraddle(uint currentCellId, uint otherCellId)
    {
        // Both cells use a Leaf BSP (contains any point) and are reciprocally portalled at the same
        // plane (local x=2.5), so the candidate set is {both} from EITHER seed and the sphere center
        // is inside BOTH cells' BSPs. The pick must return the CURRENT cell (hysteresis), not flip to
        // the neighbour. Testing both seed directions guarantees a deterministic failure on the
        // unordered pick (it returns the same enumeration-first cell regardless of which is current).
        ushort currentLow = (ushort)(currentCellId & 0xFFFF);
        ushort otherLow   = (ushort)(otherCellId & 0xFFFF);

        var current = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherLow,   flags: 0);
        var other   = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, currentLow, flags: 0);

        var cache = new PhysicsDataCache();
        cache.RegisterCellStructForTest(currentCellId, current);
        cache.RegisterCellStructForTest(otherCellId, other);

        // Center straddles the portal plane at local x=2.5 (both cells), inside both Leaf BSPs.
        var sphereCenter = new Vector3(2.0f, 0f, 2.5f);

        uint containing = CellTransit.FindCellSet(
            cache, sphereCenter, sphereRadius: 0.5f,
            currentCellId: currentCellId,
            out var cellSet);

        Assert.Contains(currentCellId, cellSet);
        Assert.Contains(otherCellId, cellSet);
        Assert.Equal(currentCellId, containing);   // retail current-cell-first hysteresis
    }

    // The ordered-CELLARRAY contract: FindCellSet returns the candidate set in
    // retail add-order with the CURRENT cell at index 0 (retail add_cell @308766).
    // This is the invariant the verbatim pick relies on; the unordered HashSet
    // could not guarantee it.
    [Fact]
    public void FindCellSet_CurrentCellIsFirstInTheSet()
    {
        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 = new CellBSPTree { Root = new CellBSPNode { Type = BSPNodeType.Leaf } },
        };
        var cache = new PhysicsDataCache();
        cache.RegisterCellStructForTest(0xA9B40100u, cellA);
        cache.RegisterCellStructForTest(0xA9B40101u, cellB);

        // Straddle the portal plane so both cells are in the set.
        var sphereCenter = new Vector3(2.0f, 0f, 2.5f);

        CellTransit.FindCellSet(cache, sphereCenter, 0.5f, 0xA9B40100u, out var cellSet);
        Assert.Equal(0xA9B40100u, cellSet.First());   // current cell at index 0
    }

    // Interior-wins over the outdoor fallback: while an interior cell still
    // contains the centre, it wins even though the exit portal also added the
    // outdoor landcell to the set (retail interior-wins-break, pc:308814-308819).
    [Fact]
    public void IndoorWithExitPortal_InteriorWinsWhileItContainsCentre()
    {
        // Interior cell at the landblock origin with an exit portal at local x=2.5;
        // Leaf BSP contains any point. Centre at local (0,12,2.5) is INSIDE the cell
        // and NOT across the exit plane, so interior must win even though the head
        // sphere / exit logic may add the outdoor landcell.
        var exitCell = MakeCellWithPortalAtRightWall(Matrix4x4.Identity, otherCellId: 0xFFFF, flags: 0);
        var cache = new PhysicsDataCache();
        cache.RegisterCellStructForTest(0xA9B40100u, exitCell);

        var sphereCenter = new Vector3(0f, 12f, 2.5f);
        uint containing = CellTransit.FindCellSet(cache, sphereCenter, 0.5f, 0xA9B40100u, out _);
        Assert.Equal(0xA9B40100u, containing);   // interior-wins, not the outdoor landcell
    }
}