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

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// Campaign OVERHAUL S2 chunk 1
/// (<c>docs/research/2026-09-01-overhaul/s2-membership-ownership-map.md</c>
/// §3): the retail CELLARRAY and per-cell part-entry SIDE PRODUCT
/// <see cref="ShadowObjectRegistry"/> now computes from an optional whole
/// part array, beside the existing collision flood. Retail anchors:
/// <c>CPhysicsObj::calc_cross_cells_static</c> 0x00515160 (Contract A branch
/// table), <c>CPhysicsObj::find_bbox_cell_list</c> 0x00510fc0,
/// <c>CPartArray::AddPartsShadow</c> 0x00517e40 (Contract B),
/// <c>CPhysicsObj::remove_shadows_from_cells</c> 0x00511230,
/// <c>CEnvCell::find_transit_cells</c> 0x0052cae0 — all re-verified
/// 2026-09-01 through the live Ghidra bridge against <c>patchmem.gpr</c>
/// (<c>docs/research/2026-09-01-overhaul/oh1-construction-landscape-contract.md</c>).
///
/// <para>
/// A bare <see cref="ShadowObjectRegistry"/> (no installed DAT) floods
/// against an empty <c>PhysicsDataCache</c>: an outdoor seed still produces
/// the real overlapped landcells from pure LandDefs math (the same fixture
/// style <see cref="BuildShadowCellSetTests"/> and
/// <c>ShadowObjectRegistryMultiPartTests</c> already use), so every fixture
/// here stays synthetic — no installed-DAT dependency.
/// </para>
/// </summary>
public class ShadowObjectRegistryRetailCellArrayTests
{
    private const uint LbId = 0xA9B40000u;
    private const float OffX = 0f;
    private const float OffY = 0f;

    // World (12, 12, 50) -> local cell (cx=0, cy=0) -> id = LbId | 1.
    private const uint CellA = LbId | 1u;
    // World (42, 12, 50), 30 m away in X -> local cell (cx=1, cy=0) -> id = LbId | 9.
    private const uint CellB = LbId | 9u;

    private static readonly Vector3 Pos = new(12f, 12f, 50f);

    private static ShadowShape Bsp(uint gfxObjId, Vector3 localPosition = default, float radius = 1f)
        => ShadowShape.Bsp(
            gfxObjId,
            localPosition,
            Quaternion.Identity,
            scale: 1f,
            localGeometry: ShadowPartGeometry.Create(
                new FlatCollisionSphere(Vector3.Zero, radius), null));

    private static ShadowShape Cyl(uint gfxObjId, Vector3 localPosition = default, float radius = 1f)
        => ShadowShape.Cylinder(
            gfxObjId, localPosition, Quaternion.Identity, scale: 1f,
            radius: radius, cylHeight: 1f);

    // -------------------------------------------------------------------
    // Item E: existing callers (no partArray) are byte-for-byte unaffected.
    // -------------------------------------------------------------------

    [Fact]
    public void RegisterMultiPart_WithoutPartArray_NoRetailProduct()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x10u;
        var shapes = new[] { Bsp(0x0100_0001u) };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, shapes,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId);

        Assert.False(reg.TryGetRetailCellArray(entityId, out var cells));
        Assert.Empty(cells);
        Assert.Equal(RetailCellArrayRoute.None, reg.GetRetailCellArrayRoute(entityId));
        foreach (uint cellId in reg.GetOwnerCells(entityId))
            Assert.Empty(reg.GetRetailPartEntriesInCell(cellId));
    }

    [Fact]
    public void Register_SingleShapeWithoutPartArray_NoRetailProduct()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x11u;

        reg.Register(entityId, 0x0100_0002u, Pos, Quaternion.Identity, 1f, OffX, OffY, LbId);

        Assert.False(reg.TryGetRetailCellArray(entityId, out var cells));
        Assert.Empty(cells);
        Assert.Equal(RetailCellArrayRoute.None, reg.GetRetailCellArrayRoute(entityId));
    }

    // -------------------------------------------------------------------
    // The bbox route (find_bbox_cell_list 0x00510fc0) is the SAME primitive
    // the collision flood uses for a single BSP-shape part array fed as both
    // `shapes` and `partArray`, and supplying a part array never touches the
    // existing collision product.
    // -------------------------------------------------------------------

    [Fact]
    public void RegisterMultiPart_WithPartArray_BoundingBoxRouteMatchesCollisionFloodForTheSamePartArray()
    {
        var withPartArray = new ShadowObjectRegistry();
        var withoutPartArray = new ShadowObjectRegistry();
        const uint entityId = 0x12u;
        IReadOnlyList<ShadowShape> parts = new[] { Bsp(0x0100_0044u, radius: 2f) };

        withPartArray.RegisterMultiPart(entityId, Pos, Quaternion.Identity, parts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            seedCellId: CellA, isStatic: true, partArray: parts);
        withoutPartArray.RegisterMultiPart(entityId, Pos, Quaternion.Identity, parts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            seedCellId: CellA, isStatic: true);

        Assert.Equal(RetailCellArrayRoute.BoundingBox, withPartArray.GetRetailCellArrayRoute(entityId));
        Assert.True(withPartArray.TryGetRetailCellArray(entityId, out var retailCells));
        Assert.NotEmpty(retailCells); // the fixture must actually exercise a flood

        // Retail's bbox route and RegisterMultiPart's own BSP collision
        // dispatch share one primitive (CPhysicsObj::find_bbox_cell_list
        // 0x00510fc0) when fed the identical single-part array as both
        // `shapes` and `partArray`, so the two products agree exactly. This
        // is the independent ground truth now that ComputeStaticRenderCells
        // (Campaign OVERHAUL S2 chunk 2) is deleted along with its only
        // production consumer.
        Assert.Equal(withPartArray.GetOwnerCells(entityId), retailCells);

        // Supplying a part array must not perturb the pre-existing collision
        // product — same registration, same result either way.
        Assert.Equal(withoutPartArray.GetOwnerCells(entityId), withPartArray.GetOwnerCells(entityId));
    }

    // -------------------------------------------------------------------
    // Contract A branch table: (state & 0x10000) == 0 && has a Cylinder
    // shape -> cylsphere route; otherwise (including the same part array
    // with the state bit set) -> bbox route.
    // -------------------------------------------------------------------

    [Fact]
    public void RegisterMultiPart_PartArrayRoute_DispatchesOnStateBitAndCylinderPresence()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x13u;
        IReadOnlyList<ShadowShape> mixed = new[]
        {
            Cyl(0x3001u),                                  // part 0: at the entity origin (CellA)
            Bsp(0x3002u, new Vector3(30f, 0f, 0f)),         // part 1: 30 m away in X (CellB)
        };

        // State bit clear + a Cylinder present -> cylsphere route
        // (CObjCell::find_cell_list 0x0052b9f0), flooded from the cylinder
        // only — the bsp part 30 m away must not pull in CellB.
        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, mixed,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId, partArray: mixed);

        Assert.Equal(RetailCellArrayRoute.Cylsphere, reg.GetRetailCellArrayRoute(entityId));
        Assert.True(reg.TryGetRetailCellArray(entityId, out var cylCells));
        Assert.Equal(new[] { CellA }, cylCells);

        var cylEntries = reg.GetRetailPartEntriesInCell(CellA)
            .Where(e => e.EntityId == entityId)
            .OrderBy(e => e.PartIndex)
            .ToList();
        // AddPartsShadow registers EVERY part per cell, not just the ones
        // that contributed to crossing it (Contract B).
        Assert.Equal(2, cylEntries.Count);
        Assert.Equal(0, cylEntries[0].PartIndex);
        Assert.Equal(0x3001u, cylEntries[0].GfxObjId);
        Assert.Equal(1, cylEntries[1].PartIndex);
        Assert.Equal(0x3002u, cylEntries[1].GfxObjId);
        Assert.False(cylEntries[0].ClipPlanesRequired); // single-cell CELLARRAY
        Assert.False(cylEntries[1].ClipPlanesRequired);

        // Re-register the SAME part array with the HAS_PHYSICS_BSP_PS state
        // bit set -> bbox route (CPhysicsObj::find_bbox_cell_list 0x00510fc0)
        // regardless of the cylinder's presence, flooded from the surviving
        // bsp part -> pulls in CellB too.
        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, mixed,
            state: 0x10000u, flags: EntityCollisionFlags.None, OffX, OffY, LbId, partArray: mixed);

        Assert.Equal(RetailCellArrayRoute.BoundingBox, reg.GetRetailCellArrayRoute(entityId));
        Assert.True(reg.TryGetRetailCellArray(entityId, out var bboxCells));
        Assert.Equal(new[] { CellA, CellB }, bboxCells);

        foreach (uint cellId in bboxCells)
        {
            var entries = reg.GetRetailPartEntriesInCell(cellId)
                .Where(e => e.EntityId == entityId)
                .OrderBy(e => e.PartIndex)
                .ToList();
            Assert.Equal(2, entries.Count);
            Assert.Equal(0, entries[0].PartIndex);
            Assert.Equal(1, entries[1].PartIndex);
            // More than one CELLARRAY member -> clip planes required (Contract B).
            Assert.True(entries[0].ClipPlanesRequired);
            Assert.True(entries[1].ClipPlanesRequired);
        }
    }

    [Fact]
    public void RegisterMultiPart_RouteIsDecidedByCollisionCylspheres_NotByTheVisualPartArray()
    {
        // Contract A: GetNumCylsphere() reads the Setup's authored CylSpheres,
        // which acdream carries as the Cylinder shapes of the COLLISION
        // dispatch. A visual part array (chunk 1b passes visual parts, which
        // are never cylinders) must not change the route.
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x14u;
        IReadOnlyList<ShadowShape> collision = new[] { Cyl(0x3001u) };
        IReadOnlyList<ShadowShape> visualParts = new[]
        {
            Bsp(0x3002u, new Vector3(30f, 0f, 0f)),         // a visual part 30 m away (CellB)
        };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, collision,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId, partArray: visualParts);

        // Cylsphere route: flooded from the authored cylsphere at the origin,
        // not from the far visual part.
        Assert.Equal(RetailCellArrayRoute.Cylsphere, reg.GetRetailCellArrayRoute(entityId));
        Assert.True(reg.TryGetRetailCellArray(entityId, out var cells));
        Assert.Equal(new[] { CellA }, cells);
        // ...but the entries are the VISUAL parts (AddPartsShadow walks the part array).
        var entries = reg.GetRetailPartEntriesInCell(CellA).Where(e => e.EntityId == entityId).ToList();
        Assert.Single(entries);
        Assert.Equal(0x3002u, entries[0].GfxObjId);

        // No cylsphere in the collision dispatch -> bbox route over the visual parts.
        IReadOnlyList<ShadowShape> bspCollision = new[] { Bsp(0x3001u, Vector3.Zero) };
        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, bspCollision,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId, partArray: visualParts);
        Assert.Equal(RetailCellArrayRoute.BoundingBox, reg.GetRetailCellArrayRoute(entityId));
    }

    // -------------------------------------------------------------------
    // Deregister is the exact inverse transaction.
    // -------------------------------------------------------------------

    [Fact]
    public void Deregister_ClearsRetailCellArrayAndEveryPerCellEntry()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x14u;
        IReadOnlyList<ShadowShape> parts = new[]
        {
            Cyl(0x4001u),
            Bsp(0x4002u, new Vector3(30f, 0f, 0f)),
        };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, parts,
            state: 0x10000u, flags: EntityCollisionFlags.None, OffX, OffY, LbId, partArray: parts);
        Assert.True(reg.TryGetRetailCellArray(entityId, out var cellsBeforeRemoval));
        Assert.NotEmpty(cellsBeforeRemoval);
        var trackedCells = cellsBeforeRemoval.ToArray();

        reg.Deregister(entityId);

        Assert.False(reg.TryGetRetailCellArray(entityId, out var cellsAfterRemoval));
        Assert.Empty(cellsAfterRemoval);
        Assert.Equal(RetailCellArrayRoute.None, reg.GetRetailCellArrayRoute(entityId));
        foreach (uint cellId in trackedCells)
            Assert.Empty(reg.GetRetailPartEntriesInCell(cellId));
    }

    // -------------------------------------------------------------------
    // UpdatePosition / CommitSetPosition recompute the retained product at
    // the new seed/position — the same flood rules, run again.
    // -------------------------------------------------------------------

    [Fact]
    public void UpdatePosition_WithRetainedPartArray_RecomputesRetailCellArray()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x15u;
        IReadOnlyList<ShadowShape> parts = new[] { Cyl(0x5001u) };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, parts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId, partArray: parts);
        Assert.True(reg.TryGetRetailCellArray(entityId, out var before));
        Assert.Equal(new[] { CellA }, before);

        var moved = new Vector3(42f, 12f, 50f); // 30 m away in X -> CellB
        reg.UpdatePosition(entityId, moved, Quaternion.Identity, OffX, OffY, LbId);

        Assert.True(reg.TryGetRetailCellArray(entityId, out var after));
        Assert.Equal(new[] { CellB }, after);
        var movedEntries = reg.GetRetailPartEntriesInCell(CellB)
            .Where(e => e.EntityId == entityId).ToList();
        Assert.Single(movedEntries);
        Assert.Equal(0x5001u, movedEntries[0].GfxObjId);
        Assert.DoesNotContain(
            reg.GetRetailPartEntriesInCell(CellA),
            e => e.EntityId == entityId);
    }

    // -------------------------------------------------------------------
    // Campaign OVERHAUL S2 chunk 4: "one array, two products" on the move
    // path too. Retail's SetPositionInternal (pc:283399) republishes BOTH
    // the collision CShadowObj list and the retail render product from the
    // SAME transition cell_array (pc:283536-283537) — never a second,
    // independently-flooded array. The retail array must therefore equal
    // GetOwnerCells after every CommitSetPosition variant.
    // -------------------------------------------------------------------

    [Fact]
    public void CommitSetPosition_NoneAction_PublishesRetailProductFromTheRetainedCells()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x16u;
        IReadOnlyList<ShadowShape> parts = new[] { Cyl(0x6001u) };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, parts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            isStatic: false, partArray: parts);
        Assert.True(reg.TryGetRetailCellArray(entityId, out var before));
        Assert.Equal(new[] { CellA }, before);

        // A .None commit carries no transition cell_array of its own (it
        // maps to retail's "cell did not change" branch, e.g. ForceIntoCell
        // with changedCell == false) — CommitSetPosition's None action
        // republishes at the RETAINED cells (CellA), not a fresh flood from
        // the new world position, even though (42,12,50) would geometrically
        // resolve to CellB. Both products must agree either way.
        var moved = new Vector3(42f, 12f, 50f);
        reg.CommitSetPosition(
            entityId,
            moved,
            Quaternion.Identity,
            seedCellId: CellB,
            worldOffsetX: OffX,
            worldOffsetY: OffY,
            action: PhysicsShadowCommitAction.None,
            crossCellIds: ImmutableArray<uint>.Empty);

        Assert.Equal(new[] { CellA }, reg.GetOwnerCells(entityId));
        Assert.True(reg.TryGetRetailCellArray(entityId, out var after));
        Assert.Equal(reg.GetOwnerCells(entityId), after);
    }

    [Fact]
    public void CommitSetPosition_ReplaceAction_PublishesRetailProductFromTheTransitionCellArray()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x18u;
        IReadOnlyList<ShadowShape> parts = new[] { Cyl(0x6101u) };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, parts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            isStatic: false, partArray: parts);
        Assert.True(reg.TryGetRetailCellArray(entityId, out var before));
        Assert.Equal(new[] { CellA }, before);

        // .Replace supplies the transition's own crossCellIds — retail's
        // arg2->cell_array. Both products move to it directly; there is no
        // second, independently-computed cell array to disagree with it.
        var moved = new Vector3(42f, 12f, 50f);
        reg.CommitSetPosition(
            entityId,
            moved,
            Quaternion.Identity,
            seedCellId: CellB,
            worldOffsetX: OffX,
            worldOffsetY: OffY,
            action: PhysicsShadowCommitAction.Replace,
            crossCellIds: [CellB]);

        Assert.Equal(new[] { CellB }, reg.GetOwnerCells(entityId));
        Assert.True(reg.TryGetRetailCellArray(entityId, out var after));
        Assert.Equal(reg.GetOwnerCells(entityId), after);
    }

    [Fact]
    public void CommitSetPosition_KeepWhenEmpty_LeavesBothProductsUntouched()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x19u;
        IReadOnlyList<ShadowShape> parts = new[] { Cyl(0x6201u) };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, parts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            isStatic: false, partArray: parts);
        Assert.True(reg.TryGetRetailCellArray(entityId, out var before));
        Assert.Equal(new[] { CellA }, before);

        // Retail's num_cells > 0 gate (pc:283534/pc:283540): an EMPTY
        // transition cell_array leaves the previous shadows exactly as they
        // were for BOTH products — no republish of either.
        reg.CommitSetPosition(
            entityId,
            Pos,
            Quaternion.Identity,
            seedCellId: CellA,
            worldOffsetX: OffX,
            worldOffsetY: OffY,
            action: PhysicsShadowCommitAction.Preserve,
            crossCellIds: ImmutableArray<uint>.Empty);

        Assert.Equal(new[] { CellA }, reg.GetOwnerCells(entityId));
        Assert.True(reg.TryGetRetailCellArray(entityId, out var after));
        Assert.Equal(new[] { CellA }, after);
    }

    // -------------------------------------------------------------------
    // ReplaceMultiPartPayload is retail's SetPart: it swaps which parts
    // occupy the CURRENT CELLARRAY without re-flooding.
    // -------------------------------------------------------------------

    [Fact]
    public void ReplaceMultiPartPayload_SwapsPartArrayWithoutReflooding()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x17u;
        IReadOnlyList<ShadowShape> initial = new[] { Cyl(0x7001u) };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, initial,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId, partArray: initial);
        Assert.True(reg.TryGetRetailCellArray(entityId, out var before));
        Assert.Equal(new[] { CellA }, before);
        Assert.Equal(RetailCellArrayRoute.Cylsphere, reg.GetRetailCellArrayRoute(entityId));

        IReadOnlyList<ShadowShape> replacement = new[] { Cyl(0x7002u), Cyl(0x7003u) };
        reg.ReplaceMultiPartPayload(entityId, Pos, Quaternion.Identity, replacement,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId, partArray: replacement);

        Assert.True(reg.TryGetRetailCellArray(entityId, out var after));
        // No reflood: the CELLARRAY is unchanged (still CellA only).
        Assert.Equal(before, after);
        // The route stays whatever the LAST recompute (at registration)
        // decided; ReplaceMultiPartPayload does not re-run the dispatch.
        Assert.Equal(RetailCellArrayRoute.Cylsphere, reg.GetRetailCellArrayRoute(entityId));

        var entries = reg.GetRetailPartEntriesInCell(CellA)
            .Where(e => e.EntityId == entityId)
            .OrderBy(e => e.PartIndex)
            .ToList();
        Assert.Equal(2, entries.Count);
        Assert.Equal(0x7002u, entries[0].GfxObjId);
        Assert.Equal(0x7003u, entries[1].GfxObjId);
        Assert.DoesNotContain(entries, e => e.GfxObjId == 0x7001u);
    }

    // -------------------------------------------------------------------
    // Campaign OVERHAUL S2 chunk 3: one flood per registration. Both
    // _entityToCells/_cells (collision) and the retail render product now
    // come from the SAME CELLARRAY when a caller supplies partArray — a
    // decorative non-BSP-colliding visual part widens COLLISION membership
    // too, not just the retail product. The BSP test still decides contact
    // at query time; only membership (which cells hold a row at all) widens.
    // -------------------------------------------------------------------

    [Fact]
    public void RegisterMultiPart_DecorativePartArrayEntry_WidensCollisionRowsToo()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x20u;
        const uint collidingGfxObj = 0xAAAA0001u;
        const uint decorativeGfxObj = 0xBBBB0001u;

        // The entity's actual COLLISION geometry is a single BSP part at the
        // entity's own origin (CellA only, on its own — AP-152's exclusive
        // collision dispatch).
        IReadOnlyList<ShadowShape> collisionShapes = new[] { Bsp(collidingGfxObj) };
        // Its WHOLE VISUAL part array (chunk 1b's partArray input) additionally
        // carries a decorative part 30 m away with no collision of its own.
        // ShadowShapeBuilder.FromStaticRenderParts/FromSetupRenderParts tag
        // EVERY visual part CollisionType.BSP as a pure geometry carrier
        // regardless of whether its GfxObj has a real physics BSP, so this
        // mirrors production exactly.
        IReadOnlyList<ShadowShape> partArray = new[]
        {
            Bsp(collidingGfxObj),
            Bsp(decorativeGfxObj, new Vector3(30f, 0f, 0f)),
        };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, collisionShapes,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            partArray: partArray);

        // Retail CELLARRAY reaches both cells — the decorative part's box
        // pulls in CellB even though it cannot collide.
        Assert.True(reg.TryGetRetailCellArray(entityId, out var retailCells));
        Assert.Equal(new[] { CellA, CellB }, retailCells);
        Assert.Equal(RetailCellArrayRoute.BoundingBox, reg.GetRetailCellArrayRoute(entityId));

        // Chunk 3: the SAME array now drives collision. Retail == collision
        // by construction, not coincidence.
        Assert.Equal(retailCells, reg.GetOwnerCells(entityId));

        foreach (uint cellId in new[] { CellA, CellB })
        {
            var collisionRows = reg.GetObjectsInCell(cellId)
                .Where(e => e.EntityId == entityId)
                .ToList();
            Assert.Single(collisionRows);
            Assert.Equal(collidingGfxObj, collisionRows[0].GfxObjId);

            // The decorative part never appears as a COLLISION row (AP-152:
            // the collision dispatch stays BSP-exclusive over collisionShapes)
            // — only as a retail render part entry.
            Assert.DoesNotContain(collisionRows, e => e.GfxObjId == decorativeGfxObj);

            var partEntries = reg.GetRetailPartEntriesInCell(cellId)
                .Where(e => e.EntityId == entityId)
                .Select(e => e.GfxObjId)
                .ToList();
            Assert.Contains(collidingGfxObj, partEntries);
            Assert.Contains(decorativeGfxObj, partEntries);
        }
    }

    [Fact]
    public void RegisterMultiPart_WithoutDecorativeParts_RetailArrayStillEqualsCollisionCells()
    {
        // BSP-only shapes with partArray == shapes: retail array and
        // collision cells must agree exactly, whether or not a partArray is
        // supplied at all (item F: "registering with partArray and without
        // must produce identical _entityToCells for BSP-only shapes").
        var withPartArray = new ShadowObjectRegistry();
        var withoutPartArray = new ShadowObjectRegistry();
        const uint entityId = 0x21u;
        IReadOnlyList<ShadowShape> shapes = new[] { Bsp(0x0100_0055u, radius: 2f) };

        withPartArray.RegisterMultiPart(entityId, Pos, Quaternion.Identity, shapes,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            seedCellId: CellA, isStatic: true, partArray: shapes);
        withoutPartArray.RegisterMultiPart(entityId, Pos, Quaternion.Identity, shapes,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            seedCellId: CellA, isStatic: true);

        Assert.Equal(
            withoutPartArray.GetOwnerCells(entityId),
            withPartArray.GetOwnerCells(entityId));
        Assert.True(withPartArray.TryGetRetailCellArray(entityId, out var retailCells));
        Assert.Equal(withPartArray.GetOwnerCells(entityId), retailCells);
    }

    // -------------------------------------------------------------------
    // Campaign OVERHAUL S2 chunk 3 item B: the staged
    // TryPrepareSetPosition/TryApplySetPosition pipeline must carry the
    // retail render product exactly like the direct CommitSetPosition path
    // — the chunk-1 gap where InstallOwnerState never seeded the staging
    // registry's retail dictionaries, so its own internal Contract-A
    // recompute silently no-opped and the applied commit dropped the retail
    // product on the floor.
    // -------------------------------------------------------------------

    [Fact]
    public void StagedSetPosition_WithRetainedPartArray_MovesBothProductsTogether()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x30u;
        IReadOnlyList<ShadowShape> parts = new[] { Cyl(0x8001u) };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, parts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId, partArray: parts);
        Assert.True(reg.TryGetRetailCellArray(entityId, out var before));
        Assert.Equal(new[] { CellA }, before);
        Assert.Equal(new[] { CellA }, reg.GetOwnerCells(entityId));

        var moved = new Vector3(42f, 12f, 50f); // 30 m away in X -> CellB
        Assert.True(reg.TryPrepareSetPosition(
            entityId,
            moved,
            Quaternion.Identity,
            seedCellId: CellB,
            worldOffsetX: OffX,
            worldOffsetY: OffY,
            PhysicsShadowCommitAction.Replace,
            crossCellIds: [CellB],
            provenShapeless: false,
            suspendOwner: false,
            out var prepared));

        // Not yet applied — both products still describe the OLD position.
        Assert.Equal(new[] { CellA }, reg.GetOwnerCells(entityId));
        Assert.True(reg.TryGetRetailCellArray(entityId, out var stillBefore));
        Assert.Equal(new[] { CellA }, stillBefore);

        Assert.True(reg.TryApplySetPosition(prepared!, out var receipt));
        Assert.True(receipt.Mutated);

        Assert.Equal(new[] { CellB }, reg.GetOwnerCells(entityId));
        Assert.True(reg.TryGetRetailCellArray(entityId, out var after));
        Assert.Equal(new[] { CellB }, after);
        Assert.Equal(RetailCellArrayRoute.Cylsphere, reg.GetRetailCellArrayRoute(entityId));

        var partEntries = reg.GetRetailPartEntriesInCell(CellB)
            .Where(e => e.EntityId == entityId).ToList();
        Assert.Single(partEntries);
        Assert.Equal(0x8001u, partEntries[0].GfxObjId);
        Assert.DoesNotContain(
            reg.GetRetailPartEntriesInCell(CellA), e => e.EntityId == entityId);

        var collisionRows = reg.GetObjectsInCell(CellB)
            .Where(e => e.EntityId == entityId).ToList();
        Assert.Single(collisionRows);
        Assert.Equal(0x8001u, collisionRows[0].GfxObjId);
        Assert.DoesNotContain(
            reg.GetObjectsInCell(CellA), e => e.EntityId == entityId);
    }

    [Fact]
    public void StagedSetPosition_KeepWhenEmpty_PreservesBothProductsTogether()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x31u;
        IReadOnlyList<ShadowShape> parts = new[] { Cyl(0x8101u) };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, parts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId, partArray: parts);
        Assert.True(reg.TryGetRetailCellArray(entityId, out var before));
        Assert.Equal(new[] { CellA }, before);
        Assert.Equal(new[] { CellA }, reg.GetOwnerCells(entityId));

        // seedCellId: 0 with the Recalculate action resolves NO seed at all
        // (landblockId derives from seedCellId, so it is also 0 —
        // DeriveOutdoorSeed's own guard) — retail keeps the previous
        // shadows (SetPositionInternal num_cells gate, pc:283540). The
        // staged pipeline must honor this for BOTH products, not just
        // collision.
        Assert.True(reg.TryPrepareSetPosition(
            entityId,
            new Vector3(999f, 999f, 50f),
            Quaternion.Identity,
            seedCellId: 0u,
            worldOffsetX: OffX,
            worldOffsetY: OffY,
            PhysicsShadowCommitAction.Recalculate,
            crossCellIds: ImmutableArray<uint>.Empty,
            provenShapeless: false,
            suspendOwner: false,
            out var prepared));
        Assert.True(reg.TryApplySetPosition(prepared!, out _));

        Assert.Equal(new[] { CellA }, reg.GetOwnerCells(entityId));
        Assert.True(reg.TryGetRetailCellArray(entityId, out var after));
        Assert.Equal(new[] { CellA }, after);
        Assert.Equal(RetailCellArrayRoute.Cylsphere, reg.GetRetailCellArrayRoute(entityId));

        var partEntries = reg.GetRetailPartEntriesInCell(CellA)
            .Where(e => e.EntityId == entityId).ToList();
        Assert.Single(partEntries);
        Assert.Equal(0x8101u, partEntries[0].GfxObjId);
    }

    // -------------------------------------------------------------------
    // Campaign OVERHAUL S2 chunk 4: AttachChild/DetachChild — retail's
    // add_shadows_to_cells child-inheritance recursion (Contract B). An
    // attached projection (equipped weapon/shield/ammunition) owns no
    // independent collision shapes; it inherits the root's CELLARRAY and
    // gets PART ENTRIES only, never a collision row.
    // -------------------------------------------------------------------

    private static IReadOnlyList<ShadowShape> ChildParts(params uint[] gfxObjIds)
    {
        var shapes = new ShadowShape[gfxObjIds.Length];
        for (int i = 0; i < gfxObjIds.Length; i++)
            shapes[i] = Bsp(gfxObjIds[i]);
        return shapes;
    }

    [Fact]
    public void AttachChild_GivesChildTheRootsArrayAndEntries()
    {
        var reg = new ShadowObjectRegistry();
        const uint rootId = 0x40u;
        const uint childId = 0x41u;
        IReadOnlyList<ShadowShape> rootParts = new[] { Cyl(0x9001u) };

        reg.RegisterMultiPart(rootId, Pos, Quaternion.Identity, rootParts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            partArray: rootParts);
        Assert.True(reg.TryGetRetailCellArray(rootId, out var rootCells));
        Assert.Equal(new[] { CellA }, rootCells);

        IReadOnlyList<ShadowShape> childParts = ChildParts(0xC001u, 0xC002u);
        Assert.True(reg.AttachChild(childId, rootId, childParts));

        Assert.True(reg.TryGetRetailCellArray(childId, out var childCells));
        Assert.Equal(rootCells, childCells);

        var entries = reg.GetRetailPartEntriesInCell(CellA)
            .Where(e => e.EntityId == childId)
            .OrderBy(e => e.PartIndex)
            .ToList();
        Assert.Equal(2, entries.Count);
        Assert.Equal(0xC001u, entries[0].GfxObjId);
        Assert.Equal(0xC002u, entries[1].GfxObjId);

        // Never a collision row — acdream's attached projections own none.
        Assert.Empty(reg.GetOwnerCells(childId));
        Assert.DoesNotContain(
            reg.GetObjectsInCell(CellA),
            e => e.EntityId == childId);
    }

    [Fact]
    public void AttachChild_RootMove_RepublishesTheChild()
    {
        var reg = new ShadowObjectRegistry();
        const uint rootId = 0x42u;
        const uint childId = 0x43u;
        IReadOnlyList<ShadowShape> rootParts = new[] { Cyl(0x9101u) };

        reg.RegisterMultiPart(rootId, Pos, Quaternion.Identity, rootParts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            isStatic: false, partArray: rootParts);
        Assert.True(reg.AttachChild(childId, rootId, ChildParts(0xC101u)));
        Assert.True(reg.TryGetRetailCellArray(childId, out var before));
        Assert.Equal(new[] { CellA }, before);

        var moved = new Vector3(42f, 12f, 50f); // -> CellB
        reg.CommitSetPosition(
            rootId,
            moved,
            Quaternion.Identity,
            seedCellId: CellB,
            worldOffsetX: OffX,
            worldOffsetY: OffY,
            action: PhysicsShadowCommitAction.Replace,
            crossCellIds: [CellB]);

        Assert.True(reg.TryGetRetailCellArray(rootId, out var rootAfter));
        Assert.Equal(new[] { CellB }, rootAfter);
        Assert.True(reg.TryGetRetailCellArray(childId, out var childAfter));
        Assert.Equal(rootAfter, childAfter);

        Assert.DoesNotContain(
            reg.GetRetailPartEntriesInCell(CellA),
            e => e.EntityId == childId);
        var movedEntries = reg.GetRetailPartEntriesInCell(CellB)
            .Where(e => e.EntityId == childId).ToList();
        Assert.Single(movedEntries);
        Assert.Equal(0xC101u, movedEntries[0].GfxObjId);
    }

    [Fact]
    public void DetachChild_ClearsTheChildsProducts()
    {
        var reg = new ShadowObjectRegistry();
        const uint rootId = 0x44u;
        const uint childId = 0x45u;
        IReadOnlyList<ShadowShape> rootParts = new[] { Cyl(0x9201u) };

        reg.RegisterMultiPart(rootId, Pos, Quaternion.Identity, rootParts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            partArray: rootParts);
        Assert.True(reg.AttachChild(childId, rootId, ChildParts(0xC201u)));
        Assert.True(reg.TryGetRetailCellArray(childId, out _));

        Assert.True(reg.DetachChild(childId));

        Assert.False(reg.TryGetRetailCellArray(childId, out var afterCells));
        Assert.Empty(afterCells);
        Assert.DoesNotContain(
            reg.GetRetailPartEntriesInCell(CellA),
            e => e.EntityId == childId);
        // The root itself is untouched.
        Assert.True(reg.TryGetRetailCellArray(rootId, out var rootCells));
        Assert.Equal(new[] { CellA }, rootCells);

        // A second detach is a no-op, not an error.
        Assert.False(reg.DetachChild(childId));
    }

    [Fact]
    public void Deregister_RootCascadesDetachOfAttachedChildren()
    {
        var reg = new ShadowObjectRegistry();
        const uint rootId = 0x46u;
        const uint childId = 0x47u;
        IReadOnlyList<ShadowShape> rootParts = new[] { Cyl(0x9301u) };

        reg.RegisterMultiPart(rootId, Pos, Quaternion.Identity, rootParts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            partArray: rootParts);
        Assert.True(reg.AttachChild(childId, rootId, ChildParts(0xC301u)));

        reg.Deregister(rootId);

        Assert.False(reg.TryGetRetailCellArray(rootId, out _));
        Assert.False(reg.TryGetRetailCellArray(childId, out var childCells));
        Assert.Empty(childCells);
        Assert.DoesNotContain(
            reg.GetRetailPartEntriesInCell(CellA),
            e => e.EntityId == childId);
    }

    [Fact]
    public void AttachChild_NestedChildOfAChild_ResolvesToTheRoot()
    {
        var reg = new ShadowObjectRegistry();
        const uint rootId = 0x48u;
        const uint directChildId = 0x49u;
        const uint grandchildId = 0x4Au;
        IReadOnlyList<ShadowShape> rootParts = new[] { Cyl(0x9401u) };

        reg.RegisterMultiPart(rootId, Pos, Quaternion.Identity, rootParts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            partArray: rootParts);
        Assert.True(reg.AttachChild(directChildId, rootId, ChildParts(0xC401u)));
        // Attach the grandchild to the DIRECT CHILD, not the root — nested
        // attachment must still resolve to the ultimate root's array.
        Assert.True(reg.AttachChild(grandchildId, directChildId, ChildParts(0xC402u)));

        Assert.True(reg.TryGetRetailCellArray(rootId, out var rootCells));
        Assert.True(reg.TryGetRetailCellArray(grandchildId, out var grandchildCells));
        Assert.Equal(rootCells, grandchildCells);

        var entries = reg.GetRetailPartEntriesInCell(CellA)
            .Where(e => e.EntityId == grandchildId).ToList();
        Assert.Single(entries);
        Assert.Equal(0xC402u, entries[0].GfxObjId);

        // Moving the root republishes BOTH the direct child and the
        // grandchild, in child-list order.
        var moved = new Vector3(42f, 12f, 50f);
        reg.CommitSetPosition(
            rootId, moved, Quaternion.Identity, seedCellId: CellB,
            worldOffsetX: OffX, worldOffsetY: OffY,
            action: PhysicsShadowCommitAction.Replace, crossCellIds: [CellB]);

        Assert.True(reg.TryGetRetailCellArray(grandchildId, out var grandchildAfter));
        Assert.Equal(new[] { CellB }, grandchildAfter);

        // Detaching the direct child cascades to the grandchild too.
        Assert.True(reg.DetachChild(directChildId));
        Assert.False(reg.TryGetRetailCellArray(grandchildId, out _));
    }

    [Fact]
    public void AttachChild_SelfAttachRejected()
    {
        var reg = new ShadowObjectRegistry();
        const uint entityId = 0x4Bu;
        IReadOnlyList<ShadowShape> rootParts = new[] { Cyl(0x9501u) };

        reg.RegisterMultiPart(entityId, Pos, Quaternion.Identity, rootParts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            partArray: rootParts);

        Assert.False(reg.AttachChild(entityId, entityId, ChildParts(0xC501u)));
    }

    [Fact]
    public void AttachChild_CycleRejected_RootUnaffected()
    {
        var reg = new ShadowObjectRegistry();
        const uint rootId = 0x4Cu;
        const uint childId = 0x4Du;
        IReadOnlyList<ShadowShape> rootParts = new[] { Cyl(0x9601u) };

        reg.RegisterMultiPart(rootId, Pos, Quaternion.Identity, rootParts,
            state: 0u, flags: EntityCollisionFlags.None, OffX, OffY, LbId,
            partArray: rootParts);
        Assert.True(reg.AttachChild(childId, rootId, ChildParts(0xC601u)));
        Assert.True(reg.TryGetRetailCellArray(rootId, out var rootCellsBefore));

        // Attaching the root TO its own child would form a cycle.
        Assert.False(reg.AttachChild(rootId, childId, ChildParts(0xC602u)));

        Assert.True(reg.TryGetRetailCellArray(rootId, out var rootCellsAfter));
        Assert.Equal(rootCellsBefore, rootCellsAfter);
        Assert.Equal(new[] { CellA }, reg.GetOwnerCells(rootId));
        // The child's own attachment is unaffected by the rejected call.
        Assert.True(reg.TryGetRetailCellArray(childId, out var childCells));
        Assert.Equal(rootCellsAfter, childCells);
    }
}