acdream/src/AcDream.Core/Physics/ShadowShapeBuilder.cs

using System;
using System.Collections.Generic;
using System.Numerics;
using AcDream.Core.World;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Enums;
using DatReaderWriter.Types;

namespace AcDream.Core.Physics;

/// <summary>
/// Pure-function builder that translates a <see cref="Setup"/> into a list of
/// <see cref="ShadowShape"/>s suitable for registration via
/// <see cref="ShadowObjectRegistry.RegisterMultiPart"/>.
///
/// <para>
/// This is a DISPATCH, not a union. In priority order: (3) when ANY Part's
/// effective GfxObj has a non-null PhysicsBSP, emit one BSP shape per such
/// Part — and nothing else; otherwise (1) every CylSphere → Cylinder shape;
/// otherwise (2) every Sphere → Sphere shape; otherwise nothing at all. Local
/// transforms come from PlacementFrames[Resting | Default | first available].
/// </para>
///
/// <para>
/// Retail anchor: <c>CPhysicsObj::FindObjCollisions</c> (0x0050f050)
/// dispatches EXCLUSIVELY on <c>HAS_PHYSICS_BSP_PS</c> (0x10000)
/// (<c>0x0050f165 test dword [esi+0xa8],0x10000</c> /
/// <c>0x0050f16f je 0x50f1a2</c>): it calls
/// <c>CPartArray::FindObjCollisions</c> (the per-part BSP walk) and returns
/// (<c>0x0050f19d jmp 0x50f2b0</c>, an UNCONDITIONAL jump past both primitive
/// branches — the CylSphere loop starts at 0x50f1a2 and the Sphere loop at
/// 0x50f21d), OR walks the Setup's CylSpheres and returns
/// (<c>0x0050f1d6 jae 0x50f317</c>), OR walks the Setup's Spheres, OR — with
/// none of the three — returns the seeded <c>OK_TS</c> without synthesizing
/// any shape (<c>0x0050f22f je 0x50f31b</c>). BSP wins.
/// <c>CPhysicsPart::find_obj_collisions</c> (0x0050d8d0) tests ONLY the
/// GfxObj physics BSP; CylSpheres and Spheres are <c>Setup</c>-level arrays
/// reached through <c>CPartArray::GetCylsphere</c> (0x00518090) and
/// <c>GetSphere</c> (0x00518070), so a part has no primitive of its own.
/// </para>
///
/// <para>
/// Cell membership dispatches on the SAME flag and in the same priority:
/// <c>CPhysicsObj::calc_cross_cells</c> (0x00515230) tests
/// <c>0x10000</c> at <c>0x00515285</c> and routes a BSP-bearing object to
/// <c>CPhysicsObj::find_bbox_cell_list</c> (0x00510fc0) at
/// <c>0x0051528f jne 0x515305</c>, never reaching its cylsphere
/// (<c>0x005152d1</c>) or sorting-sphere (<c>0x005152fb</c>) branches. That
/// is why the exclusivity is enforced HERE, at emission, rather than only at
/// the query-time guard <c>Transition.BspOnlyDispatch</c>: the shape list is
/// also the input to <c>ShadowObjectRegistry.BuildFloodSpheres</c>.
/// </para>
///
/// <para>
/// AP-152 (filed and retired 2026-08-06): these three steps used to be
/// emitted ADDITIVELY — 172 of 5,935 installed Setups carry both a primitive
/// and a physics-BSP part. The collision half of that divergence was already
/// inert, because <c>Transition.BspOnlyDispatch</c> skips both primitive
/// branches whenever the wire <c>PhysicsState</c> carries 0x10000 and ACE
/// derives that bit from the same DAT flag; the live half was CELL
/// MEMBERSHIP, which had no such guard. Gating here also removes acdream's
/// undeclared dependency on the server sending the bit: the gate is derived
/// from the parts, exactly as retail's <c>CPartArray::CacheHasPhysicsBSP</c>
/// (0x00518110) derives it.
/// </para>
/// </summary>
public static class ShadowShapeBuilder
{
    /// <summary>
    /// Build the shape list for a Setup.
    /// </summary>
    /// <param name="setup">The Setup to walk.</param>
    /// <param name="entScale">The entity's overall scale factor; multiplies
    /// every radius, height, and local offset.</param>
    /// <param name="hasPhysicsBsp">Predicate: does the GfxObj with this id
    /// have a physics BSP? Production derives it from the SAME resolver that
    /// supplies <paramref name="physicsBspBounds"/>
    /// (<c>id => _physicsBspBounds(id) is not null</c>, over
    /// <c>PhysicsDataCache.GetFlatGfxObj(id)?.PhysicsBsp</c>), so the dispatch
    /// gate and the emitted geometry cannot disagree.</param>
    /// <param name="partPoseOverride">#175: per-part pose override for the
    /// BSP part shapes — the entity's motion-table DEFAULT-STATE pose (the
    /// closed pose for doors). Retail collision tests each part's LIVE
    /// <c>CPhysicsPart</c> pose, which for an idle entity is the motion
    /// table's default state, NOT the Setup's placement frame — the two
    /// differ on e.g. the Facility Hub double door (Setup 0x02000C9D:
    /// placement poses the panels AJAR at yaw −150°/−30°, y −0.44 m; the
    /// closed pose is straight). Null / short lists fall back to the
    /// placement frame per part (entities with no motion table, and the
    /// CylSphere/Sphere shapes, are unaffected — retail poses those from
    /// the setup too).</param>
    /// <param name="effectivePartGfxObjIds">Current part identities after
    /// retail <c>AnimPartChanged</c> processing. Collision keeps each Setup
    /// index and pose, but reads PhysicsBSP from the installed replacement.
    /// Null or short lists fall back to the Setup identity.</param>
    /// <param name="physicsBspBounds">The part GfxObj's physics-BSP ROOT
    /// bounding sphere AND its authored vertex-array box — retail's
    /// <c>CGfxObj::physics_sphere</c> (<c>BSPTREE::GetSphere(physics_bsp)</c>
    /// @0x005397e0) and <c>CGfxObj::gfx_bound_box</c>
    /// (<c>CPhysicsPart::GetBoundingBox</c> @0x0050d600), as ONE
    /// <see cref="ShadowPartGeometry"/>. Supplies the emitted
    /// <see cref="ShadowShape.Radius"/>, <see cref="ShadowShape.BoundsCenter"/>
    /// and <see cref="ShadowShape.LocalBoundsMin"/>/<c>Max</c> from one call,
    /// so no part of the flood geometry can be carried while another is
    /// dropped (AP-156, then #334). Null (or a null result) falls back to the
    /// loose-but-safe 2 m placeholder at the part origin — a fixture-only
    /// configuration; production always supplies it
    /// (<c>LiveEntityCollisionBuilder</c>).</param>
    public static IReadOnlyList<ShadowShape> FromSetup(
        Setup setup,
        float entScale,
        Func<uint, bool> hasPhysicsBsp,
        IReadOnlyList<Frame>? partPoseOverride = null,
        IReadOnlyList<uint>? effectivePartGfxObjIds = null,
        Func<uint, ShadowPartGeometry?>? physicsBspBounds = null)
    {
        if (setup is null) throw new ArgumentNullException(nameof(setup));
        if (hasPhysicsBsp is null) throw new ArgumentNullException(nameof(hasPhysicsBsp));

        var result = new List<ShadowShape>();

        // 0. Retail dispatch gate. CPhysicsObj::FindObjCollisions tests
        //    HAS_PHYSICS_BSP_PS FIRST (0x0050f165) and leaves the BSP branch
        //    through an unconditional jmp past both primitive loops
        //    (0x0050f19d); CPhysicsObj::calc_cross_cells tests the same flag
        //    at 0x00515285 and routes to find_bbox_cell_list. Retail derives
        //    the flag from the part array itself
        //    (CPartArray::CacheHasPhysicsBSP 0x00518110 ORs 0x10000 on the
        //    first part whose gfxobj->physics_bsp is non-null), so the gate
        //    below reads the SAME effective part identities step 3 reads —
        //    never setup.Parts directly. A gate keyed on a different identity
        //    could suppress the primitives while step 3 emitted nothing,
        //    silently deleting the entity's collision.
        bool anyPhysicsBspPart = false;
        for (int i = 0; i < setup.Parts.Count; i++)
        {
            if (hasPhysicsBsp(EffectivePartGfxObjId(setup, effectivePartGfxObjIds, i)))
            {
                anyPhysicsBspPart = true;
                break;
            }
        }

        // Steps 1 and 2 run ONLY for an object with no physics-BSP part.
        if (!anyPhysicsBspPart)
        {
            // 1. CylSpheres — each becomes a Cylinder shape.
            foreach (var cyl in setup.CylSpheres)
            {
                if (cyl.Radius <= 0f) continue;
                float baseHeight = cyl.Height > 0f ? cyl.Height : cyl.Radius * 4f;
                result.Add(ShadowShape.Cylinder(
                    gfxObjId:      0u,
                    localPosition: new Vector3(cyl.Origin.X, cyl.Origin.Y, cyl.Origin.Z) * entScale,
                    localRotation: Quaternion.Identity,
                    scale:         entScale,
                    radius:        cyl.Radius * entScale,
                    cylHeight:     baseHeight * entScale));
            }

            // 2. Spheres — only when no CylSpheres. Retail's CylSphere loop
            //    returns rather than falling into the Sphere loop
            //    (0x0050f1d6 jae 0x50f317). Each becomes a true Sphere (no
            //    height clamping): CSphere::intersects_sphere @ 0x00537A80
            //    uses 3-D distance for the overlap check, unlike CCylSphere
            //    which clips to [low_pt, high_pt].
            if (setup.CylSpheres.Count == 0)
            {
                foreach (var sph in setup.Spheres)
                {
                    if (sph.Radius <= 0f) continue;
                    result.Add(ShadowShape.Sphere(
                        gfxObjId:      0u,
                        localPosition: new Vector3(sph.Origin.X, sph.Origin.Y, sph.Origin.Z) * entScale,
                        localRotation: Quaternion.Identity,
                        scale:         entScale,
                        radius:        sph.Radius * entScale));
                }
            }
        }

        // 3. Parts — one BSP shape per part with a non-null PhysicsBSP.
        // Pose priority per part: partPoseOverride (the motion-table
        // default-state pose, #175) → placement frame → identity.
        AnimationFrame? placementFrame = ResolvePlacementFrame(setup);
        for (int i = 0; i < setup.Parts.Count; i++)
        {
            // Retail CPhysicsPart::SetPart installs AnimPartChanged's current
            // degrade array before CPartArray::FindObjCollisions reads it.
            // Keep the stable Setup part index/pose, but source collision
            // identity from that effective part when one was supplied.
            uint gfxId = EffectivePartGfxObjId(setup, effectivePartGfxObjIds, i);
            if (!hasPhysicsBsp(gfxId)) continue;

            Frame partFrame;
            if (partPoseOverride is not null && i < partPoseOverride.Count)
                partFrame = partPoseOverride[i];
            else if (placementFrame is not null && i < placementFrame.Frames.Count)
                partFrame = placementFrame.Frames[i];
            else
                partFrame = new Frame { Origin = Vector3.Zero, Orientation = Quaternion.Identity };

            // The part's physics-BSP root bounding sphere — retail's
            // CGfxObj::physics_sphere, assigned BSPTREE::GetSphere(physics_bsp)
            // @0x005397e0. RADIUS AND CENTER TOGETHER: retail's per-part
            // cross-cell walk (CEnvCell::find_transit_cells @0x0052cae0,
            // reached from find_bbox_cell_list @0x00510fc0 through
            // CPartArray::calc_cross_cells_static @0x00518160) transforms the
            // sphere's CENTER through the part's own Position
            // (0x0052cb4c add eax,0x30 → Position::localtolocal) BEFORE it
            // reads the radius at 0x0052cb65 fadd [esi+0xc]. The center is not
            // the part origin: 376 of the 973 installed physics-BSP parts sit
            // further from it than half their own radius. A single resolver
            // supplies both so one cannot be taken without the other.
            // Absent bounds keep the loose-but-safe 2 m placeholder, centred
            // on the part origin because nothing better is known.
            // ShadowShape.Bsp scales radius, centre and box together.
            //
            // #334: the SAME resolver also supplies the authored vertex-array
            // box. Retail's outdoor cell membership
            // (CLandCell::add_all_outside_cells @0x00533360, reached from
            // find_bbox_cell_list @0x00510fc0) divides that box — never the
            // sphere — by square_length to build its cell rectangle, so a
            // resolver that answered only the sphere would leave that walk
            // with nothing to walk.
            ShadowPartGeometry geometry =
                physicsBspBounds?.Invoke(gfxId)
                ?? ShadowPartGeometry.Create(
                    new FlatCollisionSphere(Vector3.Zero, 2f),
                    null);

            result.Add(ShadowShape.Bsp(
                gfxObjId:      gfxId,
                localPosition: new Vector3(partFrame.Origin.X, partFrame.Origin.Y, partFrame.Origin.Z) * entScale,
                localRotation: partFrame.Orientation,
                scale:         entScale,
                localGeometry: geometry));
        }

        return result;
    }

    /// <summary>
    /// #185: build BSP shapes for a landblock-baked multi-part entity (buildings,
    /// stair runs, fences, rock clusters) from its per-part <see cref="MeshRef"/>s,
    /// for registration via <see cref="ShadowObjectRegistry.RegisterMultiPart"/>
    /// under the entity's SINGLE unique id.
    ///
    /// <para>
    /// Replaces the former per-part <c>Register(entity.Id * 256u + partIndex)</c>
    /// (GameWindow.cs) whose <c>* 256u</c> OVERFLOWED uint32 for class-prefixed
    /// landblock ids (<c>0x40</c>/<c>0x80</c>/<c>0xC0</c>…): the overflow dropped
    /// the prefix byte, so different-class entities sharing the low 24 bits
    /// collided on one shadow part-id and <c>Register</c>'s deregister-then-insert
    /// silently overwrote one entity's collision geometry — the #185 "invisible
    /// wall half-way up the stairs" (rendered steps with no collision).
    /// </para>
    ///
    /// <para>
    /// Retail anchor: a multi-part object is one <c>CPhysicsObj</c> + <c>CPartArray</c>;
    /// <c>CPhysicsObj::add_shadows_to_cells</c> (0x00514ae0) → <c>CPartArray::AddPartsShadow</c>
    /// walks the part array under the single object — no synthetic per-part id.
    /// </para>
    ///
    /// <para>
    /// Each part's local transform comes from its <see cref="MeshRef.PartTransform"/>
    /// (root-relative), decomposed to LocalPosition/LocalRotation/Scale;
    /// <c>RegisterMultiPart</c> reconstructs the world placement identically
    /// (<c>entityWorldPos + rotate(LocalPosition, entityWorldRot)</c>). Building
    /// shells are excluded — they collide via the per-LandCell building channel
    /// (<c>CSortCell::find_collisions</c>), not as shadow objects.
    /// </para>
    /// </summary>
    /// <param name="meshRefs">The entity's per-part mesh references.</param>
    /// <param name="isBuildingShell">True for <c>LandBlockInfo.Buildings[]</c> shells.</param>
    /// <param name="getGfxObj">Resolves a GfxObj id to its cached physics (BSP +
    /// bounding sphere). Production: <c>id => cache.GetGfxObj(id)</c>.</param>
    public static List<ShadowShape> FromLandblockBspParts(
        IReadOnlyList<MeshRef> meshRefs,
        bool isBuildingShell,
        Func<uint, GfxObjPhysics?> getGfxObj)
    {
        if (getGfxObj is null) throw new ArgumentNullException(nameof(getGfxObj));

        var shapes = new List<ShadowShape>();
        // Building shells collide via the building channel (retail), not shadow objects.
        if (isBuildingShell || meshRefs is null) return shapes;

        foreach (var meshRef in meshRefs)
        {
            var phys = getGfxObj(meshRef.GfxObjId);
            if (phys is null) continue;
            FlatPhysicsBsp? flat = phys.FlatPhysicsBsp;
            bool hasFlat = flat is { RootIndex: >= 0 };
            if (!hasFlat && phys.BSP?.Root is null)
                continue; // graph-only fixture seam until I6 referee removal

            // PartTransform is root-relative; decompose to local pos/rot/scale.
            if (!Matrix4x4.Decompose(meshRef.PartTransform,
                    out var pScale, out var pRot, out var pPos))
            {
                pScale = Vector3.One;
                pRot = Quaternion.Identity;
                pPos = new Vector3(meshRef.PartTransform.M41,
                                   meshRef.PartTransform.M42,
                                   meshRef.PartTransform.M43);
            }

            float partScale = pScale.X > 0f ? pScale.X : 1f;   // AC objects are uniformly scaled
            // Root bounding sphere, CENTER AND RADIUS TOGETHER — see
            // ShadowShape.BoundsCenter. Retail's per-part cross-cell walk
            // (CEnvCell::find_transit_cells @0x0052cae0) transforms
            // CGfxObj::physics_sphere's center through the part's Position
            // before using its radius; a landblock-baked part array is the
            // same CPartArray walk (CPartArray::calc_cross_cells_static
            // @0x00518160), so dropping the center here mis-places the flood
            // exactly as it did for live Setups.
            FlatCollisionSphere localBounds =
                hasFlat
                    ? flat!.Nodes[flat.RootIndex].BoundingSphere
                    : new FlatCollisionSphere(
                        phys.BoundingSphere?.Origin ?? Vector3.Zero,
                        phys.BoundingSphere?.Radius ?? 1f);

            // #334: the same cached record carries the authored vertex-array
            // box (CGfxObj::gfx_bound_box), which retail's outdoor extent walk
            // — CLandCell::add_all_outside_cells @0x00533360 — divides by
            // square_length. Landblock-baked part arrays are exactly the
            // population whose extent exceeds one 24 m land cell, so the
            // sphere alone cannot describe their membership.
            ShadowPartGeometry geometry =
                ShadowPartGeometry.Create(localBounds, phys.VisualBounds);

            shapes.Add(ShadowShape.Bsp(
                gfxObjId:      meshRef.GfxObjId,
                localPosition: pPos,
                localRotation: pRot,
                scale:         partScale,
                localGeometry: geometry));
        }

        return shapes;
    }

    /// <summary>
    /// The collision identity of part <paramref name="index"/>: the installed
    /// <c>AnimPartChanged</c> replacement when one was supplied, else the
    /// Setup's own part. Shared by the step-0 dispatch gate and the step-3
    /// emission so the two can never read different identities.
    /// </summary>
    private static uint EffectivePartGfxObjId(
        Setup setup,
        IReadOnlyList<uint>? effectivePartGfxObjIds,
        int index)
        => effectivePartGfxObjIds is not null && index < effectivePartGfxObjIds.Count
            ? effectivePartGfxObjIds[index]
            : (uint)setup.Parts[index];

    /// <summary>Resolve the placement frame in priority Resting → Default →
    /// first available. Mirrors <c>SetupMesh.Flatten</c>'s convention.</summary>
    private static AnimationFrame? ResolvePlacementFrame(Setup setup)
    {
        if (setup.PlacementFrames.TryGetValue(Placement.Resting, out var resting)) return resting;
        if (setup.PlacementFrames.TryGetValue(Placement.Default, out var def))     return def;
        foreach (var kvp in setup.PlacementFrames) return kvp.Value;
        return null;
    }
}