using System;
using System.Numerics;
using AcDream.Core.Physics;
using Xunit;
using Xunit.Abstractions;
using Plane = System.Numerics.Plane;

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// Conformance tests for the retail <c>CSphere::intersects_sphere</c> collision
/// family port (2026-07-07) — dispatcher <c>0x00537A80</c> + <c>step_sphere_up</c>
/// <c>0x00537900</c> + <c>slide_sphere</c> <c>0x00537440</c> +
/// <c>land_on_sphere</c> <c>0x005379a0</c> + <c>collide_with_point</c>
/// <c>0x00537230</c> + <c>step_sphere_down</c> <c>0x00536d20</c>. Pseudocode:
/// docs/research/2026-07-07-csphere-collision-family-pseudocode.md.
///
/// <para>
/// The driving repro: the user's live report that a player packed inside a crowd
/// of monsters gets wedged and can't wiggle free, where retail leaves room to
/// shuffle out. Humanoid creatures/players collide as body <b>Spheres</b>
/// (Setup.Spheres → <see cref="ShadowShapeBuilder.FromSetup"/> emits
/// <see cref="ShadowCollisionType.Sphere"/>), so the crowd contact runs through
/// <c>Transition.SphereCollision</c>. Before this port that method was a
/// hand-rolled 3-D wall-slide with a forced fixed de-penetration (register
/// <b>TS-45</b>) — opposing radial pushes from neighbours cancelled and the
/// player wedged. The faithful family routes the slide through the shared crease
/// projection, restoring retail's tangential shuffle. Synthetic spheres only — no
/// dat dependency.
/// </para>
/// </summary>
public class SphereCollisionFamilyTests
{
    private readonly ITestOutputHelper _out;
    public SphereCollisionFamilyTests(ITestOutputHelper output) => _out = output;

    private const uint TestLandblockId = 0xA9B40000u;
    private const uint TestCellId = TestLandblockId | 0x0001u;   // landcell (0,0)

    private const float SphereRadius   = 0.48f;   // retail player capsule radius
    private const float SphereHeight   = 1.20f;
    private const float StepUpHeight   = 0.60f;
    private const float StepDownHeight = 0.04f;

    private const float CreatureRadius = 0.48f;   // a humanoid body sphere

    /// <summary>
    /// THE headline behavior: the crease slide lets a grounded player SHUFFLE
    /// AROUND a body-sphere creature that partly blocks the path, instead of
    /// sticking to it. The creature sits slightly EAST of the player's northward
    /// line; the player walks N, grazes the creature's south-west, and must slide
    /// along it (crease = collisionNormal × ground-up) and continue past.
    ///
    /// <para>
    /// This is the retail-faithful tangential slide the port restores. The
    /// pre-2026-07-07 hand-rolled SphereCollision force-pushed the contact
    /// RADIALLY to a fixed <c>combinedR + 1 cm</c> shell (shoving the player
    /// south-west, back along its approach) — TS-45. In a crowd those radial
    /// shoves from several neighbours fight each other and wedge the player; the
    /// tangential crease slide is what leaves "room to shuffle out". The player
    /// starts CLEAR (not penetrating) — a start deep inside overlapping spheres
    /// reverts in retail too (validate_transition restores curr_pos on a
    /// non-clean step, 0x0050aa70:272593), so that is not a valid repro.
    /// </para>
    /// </summary>
    [Fact]
    public void GroundedDiagonalApproach_SlidesPastOffsetCreature()
    {
        var engine = BuildEngine(out _);
        RegisterCreatureSphere(engine, 0xC0C0u, 10.35f, 12f);   // slightly EAST of the N path

        var body = MakeGroundedBody(new Vector3(10f, 10f, 0f));
        Vector3 pos = body.Position;
        uint cellId = TestCellId;
        bool grounded = true;
        var perTick = new Vector3(0f, 0.08f, 0f);   // push NORTH

        for (int tick = 0; tick < 60; tick++)
        {
            var result = engine.ResolveWithTransition(
                pos, pos + perTick, cellId,
                SphereRadius, SphereHeight, StepUpHeight, StepDownHeight,
                grounded, body: body,
                moverFlags:     ObjectInfoState.IsPlayer | ObjectInfoState.EdgeSlide,
                movingEntityId: 0);

            body.Position = result.Position;
            pos      = result.Position;
            cellId   = result.CellId;
            grounded = result.IsOnGround;
            _out.WriteLine($"tick {tick,2}: ({pos.X:F3},{pos.Y:F3})");
        }

        _out.WriteLine($"final pos=({pos.X:F3},{pos.Y:F3},{pos.Z:F3}) grounded={grounded}");

        // The creature centre is at Y=12. If the player slid around it, it ends
        // NORTH of the creature; if it stuck, it wedges near Y≈11 (surface at
        // Y = 12 − sqrt(0.96² − 0.35²) ≈ 11.11).
        Assert.True(pos.Y > 12.5f,
            $"Player must slide around the offset creature and continue north, not stick at " +
            $"its surface; got Y={pos.Y:F3}");
    }

    /// <summary>
    /// A single body-sphere creature dead ahead: the player pushing straight into
    /// it must stop AT the surface (a head-on push has no crease tangent → the
    /// slide degenerates → Collided) and must NOT penetrate or pass through.
    /// Surface contact is at Y = 11.5 − (0.48+0.48) = 10.54.
    /// </summary>
    [Fact]
    public void GroundedSingleCreature_HeadOnPush_BlocksWithoutPenetration()
    {
        var engine = BuildEngine(out _);
        RegisterCreatureSphere(engine, 0xC0B0u, 12f, 11.5f);   // due north

        var body = MakeGroundedBody(new Vector3(12f, 10f, 0f));
        Vector3 pos = body.Position;
        uint cellId = TestCellId;
        bool grounded = true;
        var perTick = new Vector3(0f, 0.08f, 0f);   // straight in

        for (int tick = 0; tick < 30; tick++)
        {
            var result = engine.ResolveWithTransition(
                pos, pos + perTick, cellId,
                SphereRadius, SphereHeight, StepUpHeight, StepDownHeight,
                grounded, body: body,
                moverFlags:     ObjectInfoState.IsPlayer | ObjectInfoState.EdgeSlide,
                movingEntityId: 0);

            body.Position = result.Position;
            pos      = result.Position;
            cellId   = result.CellId;
            grounded = result.IsOnGround;
        }

        _out.WriteLine($"final pos=({pos.X:F3},{pos.Y:F3},{pos.Z:F3})");

        Assert.True(pos.Y < 10.7f,
            $"Player must be blocked at the sphere surface (Y≈10.54), not penetrate; got Y={pos.Y:F3}");
        Assert.True(pos.Y > 10.3f,
            $"Player must actually reach the creature (not stop early); got Y={pos.Y:F3}");
    }

    /// <summary>
    /// An ETHEREAL sphere (state 0x4, non-static) is fully passable — the branch-1
    /// early-OK consume plus the caller's Layer-2 override. Guards the door/ghost
    /// passability against the family rewrite.
    /// </summary>
    [Fact]
    public void GroundedEtherealSphere_IsFullyPassable()
    {
        var engine = BuildEngine(out _);
        RegisterCreatureSphere(engine, 0xC0E0u, 12f, 11.5f,
            state: 0x4u, isCreatureFlag: false);   // ETHEREAL_PS, non-static

        var body = MakeGroundedBody(new Vector3(12f, 10f, 0f));
        Vector3 pos = body.Position;
        uint cellId = TestCellId;
        bool grounded = true;
        var perTick = new Vector3(0f, 0.08f, 0f);

        for (int tick = 0; tick < 45; tick++)
        {
            var result = engine.ResolveWithTransition(
                pos, pos + perTick, cellId,
                SphereRadius, SphereHeight, StepUpHeight, StepDownHeight,
                grounded, body: body,
                moverFlags:     ObjectInfoState.IsPlayer | ObjectInfoState.EdgeSlide,
                movingEntityId: 0);

            body.Position = result.Position;
            pos      = result.Position;
            cellId   = result.CellId;
            grounded = result.IsOnGround;
        }

        _out.WriteLine($"final pos=({pos.X:F3},{pos.Y:F3},{pos.Z:F3})");

        Assert.True(pos.Y > 12.5f,
            $"Ethereal sphere must not block (walked from 10 past the axis); got Y={pos.Y:F3}");
    }

    // ───────────────────────────────────────────────────────────────
    // Harness (mirrors CylSphereFamilyTests)
    // ───────────────────────────────────────────────────────────────

    private static PhysicsEngine BuildEngine(out PhysicsDataCache cache)
    {
        cache = new PhysicsDataCache();
        var engine = new PhysicsEngine { DataCache = cache };

        var heights = new byte[81];
        var heightTable = new float[256];   // all zero → terrain Z = 0
        engine.AddLandblock(
            landblockId:  TestLandblockId,
            terrain:      new TerrainSurface(heights, heightTable),
            cells:        Array.Empty<CellSurface>(),
            portals:      Array.Empty<PortalPlane>(),
            worldOffsetX: 0f,
            worldOffsetY: 0f);

        return engine;
    }

    /// <summary>
    /// Register a humanoid body sphere at foot height (Z = SphereRadius) so the
    /// player's foot sphere overlaps it horizontally. Flagged as a creature by
    /// default (the crowd case), mimicking a live monster's body-sphere shadow.
    /// </summary>
    private static void RegisterCreatureSphere(PhysicsEngine engine, uint entityId,
        float x, float y, float radius = CreatureRadius, uint state = 0u,
        bool isCreatureFlag = true)
    {
        engine.ShadowObjects.Register(
            entityId, gfxObjId: 0u,
            new Vector3(x, y, SphereRadius), Quaternion.Identity, radius,
            worldOffsetX: 0f, worldOffsetY: 0f, landblockId: TestLandblockId,
            collisionType: ShadowCollisionType.Sphere,
            cylHeight: 0f, scale: 1f,
            state: state,
            flags: isCreatureFlag ? EntityCollisionFlags.IsCreature : EntityCollisionFlags.None,
            isStatic: false);
    }

    private static PhysicsBody MakeGroundedBody(Vector3 position)
    {
        var floorPlane = new Plane(Vector3.UnitZ, 0f);
        var floorVerts = new[]
        {
            new Vector3(-100f, -100f, 0f),
            new Vector3( 100f, -100f, 0f),
            new Vector3( 100f,  100f, 0f),
            new Vector3(-100f,  100f, 0f),
        };

        return new PhysicsBody
        {
            Position             = position,
            Orientation          = Quaternion.Identity,
            ContactPlaneValid    = true,
            ContactPlane         = floorPlane,
            ContactPlaneCellId   = TestCellId,
            WalkablePolygonValid = true,
            WalkablePlane        = floorPlane,
            WalkableVertices     = floorVerts,
            WalkableUp           = Vector3.UnitZ,
            TransientState       = TransientStateFlags.Contact | TransientStateFlags.OnWalkable,
        };
    }
}