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

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// #137 mechanism 2 — the sliding-normal absorbing wedge (2026-07-06).
///
/// <para>
/// Retail's in-transition <c>collision_info.sliding_normal</c> has exactly ONE
/// writer besides the per-frame seed: <c>CTransition::validate_transition</c>
/// (0x0050ac21-ac30, "if collision_normal_valid → set_sliding_normal"). The
/// BSP collision layer NEVER writes it — <c>BSPTREE::find_collisions</c>'
/// Contact branch dispatches full hits to <c>step_sphere_up</c> (foot,
/// 0x0053a719) / <c>BSPTREE::slide_sphere</c> (head, 0x0053a697), and
/// <c>CSphere::slide_sphere</c> (0x00537440) slides IN-FRAME via
/// <c>add_offset_to_check_pos</c> without touching sliding_normal
/// (grep-verified: zero sliding_normal references between 0x005155 and
/// 0x00841f in acclient_2013_pseudo_c.txt). ACE mirrors this: the only
/// SetSlidingNormal call sites are CollisionInfo.cs:58 (the setter) and
/// Transition.cs:1027 (validate). The body-side persistence
/// (<c>CPhysicsObj::SetPositionInternal</c> 0x005154c2, SLIDING_TS bit-4 sync
/// at 0x005154e1) runs only on transition SUCCESS.
/// </para>
///
/// <para>
/// acdream's BSPQuery Contact branch carried stub fallbacks
/// (SetCollisionNormal + SetSlidingNormal + return Slid) instead of the real
/// slide. The leaked sliding normal survived to the transition end, the
/// unconditional body writeback persisted it, and the next frame's seed
/// projected an exactly-anti-parallel push to zero — aborting at step 0
/// BEFORE any collision test could refresh the state. Live shape: the
/// Facility Hub corridor phantom (launch-175-verify2.log:42858 — one wall
/// hit at the 0x8A02016E→0x8A02017A seam, then endless ok=False hit=no
/// zero-advance resolves; strafe escapes).
/// </para>
/// </summary>
public class Issue137SlidingNormalLifecycleTests
{
    // =========================================================================
    // Site-level pins — BSPQuery.FindCollisions Contact branch must not write
    // the transition's sliding normal (retail: only validate_transition does).
    // =========================================================================

    /// <summary>
    /// Contact foot-sphere FULL HIT with the step-up recursion unavailable
    /// (engine=null / step-up already in progress) must dispatch the real
    /// sphere slide — never the SetSlidingNormal stub.
    ///
    /// <para>
    /// Retail: a blocked step-up funnels to <c>SPHEREPATH::step_up_slide</c> →
    /// <c>CSphere::slide_sphere</c> (ACE SpherePath.cs:316 → Sphere.cs:558) —
    /// in-frame slide, no sliding_normal write. Face-on into a vertical wall
    /// while grounded: the crease projection (cross(wallN, floorN)) has no
    /// component along the movement, the slide offset is degenerate
    /// (&lt; F_EPSILON), and slide_sphere returns COLLIDED_TS (0x00537735).
    /// </para>
    /// </summary>
    [Fact]
    public void ContactFootFullHit_StepUpUnavailable_RealSlide_NoSlidingNormalWrite()
    {
        var (root, resolved) = BSPStepUpFixtures.TallWall();

        // Grounded mover pushing face-on (+X) into the 5 m wall at x=0.5
        // (normal −X). Sphere center reach 0.35+0.2=0.55 penetrates the wall.
        var from = new Vector3(0.10f, 0f, BSPStepUpFixtures.SphereRadius);
        var to   = new Vector3(0.35f, 0f, BSPStepUpFixtures.SphereRadius);
        var t    = BSPStepUpFixtures.MakeGroundedTransition(from, to);

        var localSphere = new DatReaderWriter.Types.Sphere
        {
            Origin = to,
            Radius = BSPStepUpFixtures.SphereRadius,
        };

        var result = BSPQuery.FindCollisions(
            root, resolved, t, localSphere, null,
            from, Vector3.UnitZ, 1.0f);

        Assert.False(t.CollisionInfo.SlidingNormalValid,
            "find_collisions must not write collision_info.sliding_normal — " +
            "retail's only in-transition writer is validate_transition " +
            "(0x0050ac21). A sliding normal leaked here survives to the body " +
            "writeback and absorbs the next frame's forward offset (#137).");
        Assert.True(t.CollisionInfo.CollisionNormalValid,
            "The real slide records the collision normal (CSphere::slide_sphere " +
            "→ set_collision_normal).");
        Assert.Equal(TransitionState.Collided, result);
    }

    /// <summary>
    /// Contact HEAD-sphere FULL HIT must dispatch <c>BSPTREE::slide_sphere</c>
    /// (retail 0x0053a697; ACE BSPTree.cs:202 → 310-316: the real
    /// <c>Sphere.SlideSphere</c> on GlobalSphere[0]) — never the stub.
    /// The corridor phantom's portal-side polys span head height; this is the
    /// path that recorded the (−1,0,0) normal the wedge absorbed on.
    /// </summary>
    [Fact]
    public void ContactHeadFullHit_RealSlide_NoSlidingNormalWrite()
    {
        // Raised wall: z ∈ [0.6, 5] at x=0.5, normal −X. The foot sphere
        // (center z=0.2, r=0.2 → z-span [0, 0.4]) passes under it; the head
        // sphere (center z=0.8 → z-span [0.6, 1.0]) fully hits it.
        var resolved = new Dictionary<ushort, ResolvedPolygon>();

        var floorVerts = new[]
        {
            new Vector3(-2f, -1f, 0f), new Vector3(2f, -1f, 0f),
            new Vector3(2f,  1f, 0f), new Vector3(-2f, 1f, 0f),
        };
        resolved[1] = new ResolvedPolygon
        {
            Vertices  = floorVerts,
            Plane     = new Plane(Vector3.UnitZ, 0f),
            NumPoints = 4,
            SidesType = CullMode.None,
        };

        var wallNormal = new Vector3(-1f, 0f, 0f);
        var wallVerts = new[]
        {
            new Vector3(0.5f, -1f, 0.6f),
            new Vector3(0.5f, -1f, 5f),
            new Vector3(0.5f,  1f, 5f),
            new Vector3(0.5f,  1f, 0.6f),
        };
        resolved[2] = new ResolvedPolygon
        {
            Vertices  = wallVerts,
            Plane     = new Plane(wallNormal, 0.5f),   // n·p + d = 0 at x=0.5
            NumPoints = 4,
            SidesType = CullMode.None,
        };

        var leaf = new PhysicsBSPNode
        {
            Type           = BSPNodeType.Leaf,
            BoundingSphere = new DatReaderWriter.Types.Sphere { Origin = new Vector3(0f, 0f, 2.5f), Radius = 10f },
        };
        leaf.Polygons.Add(1);
        leaf.Polygons.Add(2);

        var from = new Vector3(0.10f, 0f, BSPStepUpFixtures.SphereRadius);
        var to   = new Vector3(0.35f, 0f, BSPStepUpFixtures.SphereRadius);
        var t    = BSPStepUpFixtures.MakeGroundedTransition(from, to);

        var footSphere = new DatReaderWriter.Types.Sphere
        {
            Origin = to,
            Radius = BSPStepUpFixtures.SphereRadius,
        };
        var headSphere = new DatReaderWriter.Types.Sphere
        {
            Origin = new Vector3(to.X, to.Y, 0.8f),
            Radius = BSPStepUpFixtures.SphereRadius,
        };

        var result = BSPQuery.FindCollisions(
            leaf, resolved, t, footSphere, headSphere,
            from, Vector3.UnitZ, 1.0f);

        Assert.False(t.CollisionInfo.SlidingNormalValid,
            "Head full hit must go through the real BSPTREE::slide_sphere — " +
            "no sliding_normal write at the BSP layer (retail 0x0053a697).");
        Assert.True(t.CollisionInfo.CollisionNormalValid);
        Assert.Equal(TransitionState.Collided, result);
    }

    // =========================================================================
    // Engine-level lifecycle pin — the retail persist/absorb/clear cycle at a
    // REAL wall. Guards the fix against regressing wall behavior, and
    // documents where retail CLEARS the body's sliding state (the successful
    // transition's writeback, when no step re-records a collision).
    // =========================================================================

    private const uint CellId = 0xA9B40157u;

    private static PhysicsEngine BuildWallEngine()
    {
        var (wallRoot, wallResolved) = BSPStepUpFixtures.TallWall();

        var cell = new CellPhysics
        {
            BSP                   = new PhysicsBSPTree { Root = wallRoot },
            WorldTransform        = Matrix4x4.Identity,
            InverseWorldTransform = Matrix4x4.Identity,
            Resolved              = wallResolved,
            CellBSP               = new CellBSPTree
            {
                Root = new CellBSPNode { Type = BSPNodeType.Leaf },
            },
        };

        var engine = new PhysicsEngine();
        engine.DataCache = new PhysicsDataCache();

        // Flat terrain strip so the outdoor fall-through has something to
        // sample if it ever fires (same shape as FindEnvCollisionsMultiCellTests).
        var heights = new byte[81];
        Array.Fill(heights, (byte)0);
        engine.AddLandblock(0xA9B4FFFFu, new TerrainSurface(heights, BuildHeightTable()),
            Array.Empty<CellSurface>(), Array.Empty<PortalPlane>(),
            worldOffsetX: 0f, worldOffsetY: 0f);

        engine.DataCache.RegisterCellStructForTest(CellId, cell);
        return engine;
    }

    private static float[] BuildHeightTable()
    {
        var ht = new float[256];
        for (int i = 0; i < 256; i++) ht[i] = i * 1.0f;
        return ht;
    }

    private static PhysicsBody GroundedBody()
    {
        var body = new PhysicsBody();
        body.ContactPlaneValid = true;
        body.ContactPlane      = new Plane(Vector3.UnitZ, 0f);
        body.TransientState   |= TransientStateFlags.Contact | TransientStateFlags.OnWalkable;
        return body;
    }

    private ResolveResult ResolveForward(PhysicsEngine engine, PhysicsBody body,
        Vector3 from, Vector3 to)
        => engine.ResolveWithTransition(
            currentPos:     from,
            targetPos:      to,
            cellId:         CellId,
            sphereRadius:   BSPStepUpFixtures.SphereRadius,
            sphereHeight:   0f,     // single sphere — keeps the scenario deterministic
            stepUpHeight:   0.04f,  // cannot scale the 5 m wall
            stepDownHeight: 0.04f,
            isOnGround:     true,
            body:           body);

    /// <summary>
    /// The full retail lifecycle at a real wall:
    /// (1) a blocked face-on push persists the validate-recorded sliding
    ///     normal via the SUCCESS writeback (SetPositionInternal bit-4 sync,
    ///     0x005154e1);
    /// (2) the next exactly-anti-parallel push is absorbed by the seed
    ///     (get_object_info 0x00511d44 → adjust_offset projects to zero →
    ///     find_transitional_position's step-0 small-offset abort) — the
    ///     retail cache semantics: "still pressed against this wall";
    /// (3) an oblique push escapes along the wall tangent, the step runs
    ///     without re-recording a collision, and the successful writeback
    ///     CLEARS the body's sliding state (sliding_normal_valid==0 → bit
    ///     4 cleared).
    /// </summary>
    [Fact]
    public void WallLifecycle_PersistOnBlock_AbsorbExactAntiParallel_ClearOnEscape()
    {
        var engine = BuildWallEngine();
        var body   = GroundedBody();

        // ── 1. Face-on +X into the wall at x=0.5 (normal −X) ─────────────
        var r1 = ResolveForward(engine, body,
            from: new Vector3(0.10f, 0f, 0f),
            to:   new Vector3(0.35f, 0f, 0f));

        Assert.True(body.TransientState.HasFlag(TransientStateFlags.Sliding),
            "A blocked push must persist the validate-recorded sliding normal " +
            "(retail SetPositionInternal 0x005154c2 on transition success).");
        Assert.True(body.SlidingNormal.X < -0.9f,
            $"Persisted normal should face the mover (−X); got {body.SlidingNormal}.");
        Assert.True(r1.Position.X + BSPStepUpFixtures.SphereRadius
                    <= 0.5f + PhysicsGlobals.EPSILON * 20f,
            $"The 5 m wall must block the sphere; reach={r1.Position.X + BSPStepUpFixtures.SphereRadius:F4}.");

        // ── 2. Exactly-anti-parallel push again: absorbed frame ──────────
        var r2 = ResolveForward(engine, body,
            from: r1.Position,
            to:   r1.Position + new Vector3(0.15f, 0f, 0f));

        Assert.False(r2.Ok,
            "The seeded sliding normal projects the exactly-anti-parallel " +
            "offset to zero → step-0 abort (retail find_transitional_position " +
            "0050bfb7/0050c0ef). Faithful absorbed frame at a REAL wall.");
        Assert.True(body.TransientState.HasFlag(TransientStateFlags.Sliding),
            "A failed transition leaves the body's sliding state untouched " +
            "(retail: SetPositionInternal never runs on failure).");

        // ── 3. Oblique push escapes and CLEARS the persisted state ───────
        var r3 = ResolveForward(engine, body,
            from: r2.Position,
            to:   r2.Position + new Vector3(0.10f, 0.15f, 0f));

        Assert.True(r3.Ok, "Oblique push must escape along the wall tangent.");
        Assert.True(r3.Position.Y > r2.Position.Y + 0.05f,
            $"Expected tangential advance along +Y; got Y={r3.Position.Y:F4} " +
            $"(from {r2.Position.Y:F4}).");
        Assert.False(body.TransientState.HasFlag(TransientStateFlags.Sliding),
            "A successful transition whose steps re-record no collision must " +
            "CLEAR the body's sliding state (retail SetPositionInternal " +
            "0x005154e1: bit 4 synced from the transition's final " +
            "sliding_normal_valid, which each step clears before its insert).");
        Assert.Equal(Vector3.Zero, body.SlidingNormal);
    }
}