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

namespace AcDream.Core.Tests.Physics;

/// <summary>
/// #185 outdoor-stairs phantom (2026-07-08) — dat-free reproduction of the
/// house-on-stilts staircase jam. The stairs are a continuous, COPLANAR
/// 38.7° ramp built from stacked step-box objects (gfxObj 0x01000AC5); the
/// tread quads abut at 0.5 m seams that fall on object boundaries. Walking
/// up, at one seam the grounded forward move loses its contact plane and the
/// step-down recovery cannot reach the coplanar (at-level) continuation, so
/// <c>EdgeSlideAfterStepDownFailed</c> → <c>PrecipiceSlide</c> fabricates the
/// tread-edge normal <c>(0,±0.78,±0.62)</c>, which <c>SetSlidingNormal</c>
/// horizontalises to <c>(0,±1,0)</c> — absorbing the +Y up-stairs motion into
/// a pure sideways slide (the #137 / TS-4 family). A jump's +Z clears it.
///
/// <para>
/// Fixtures captured live this session: the player pins at world
/// <c>(131.71, 77.914, 61.485)</c> with <c>slidingNormal=(0,1,0)</c> and a
/// re-fabricated <c>collisionNormal=(0,0.78,0.62)</c>; the tread the player is
/// grounded on has world verts <c>(132.75,77.495,61.015)…</c>. The step-box
/// geometry is hydrated from the captured gfxobj dump
/// (<c>Fixtures/issue185/0x01000AC5.gfxobj.json</c>) so the test is
/// self-contained (no dat) and CI-runnable.
/// </para>
///
/// <para>
/// The step origins march +0.5 world-Y / +0.4 world-Z (matching every observed
/// <c>[resolve-bldg]</c> origin: 75.2/75.7/76.2/76.7/77.2). The player's tread
/// (k=4) is pinned to origin <c>(132.0, 77.245, 60.415)</c> by the captured
/// walkable verts. k=0..7 are registered to span the jam seam + the
/// continuation the player must climb onto.
/// </para>
/// </summary>
public class Issue185OutdoorStairsSeamReplayTests
{
    private readonly ITestOutputHelper _out;
    public Issue185OutdoorStairsSeamReplayTests(ITestOutputHelper output) => _out = output;

    private const uint StairCellId    = 0xF682002Cu;   // outdoor landcell (low16 = 0x2C < 0x100)
    private const uint StairLandblock = 0xF6820000u;
    private const uint StepGfxObjId   = 0x01000AC5u;
    private const int  StepCount      = 8;

    // A +90°-about-Z-rotated step-box maps its local tread normal
    // (-0.625,0,0.781) → world (0,-0.625,0.781) (the captured tread plane).
    private static readonly Quaternion StepRot =
        Quaternion.CreateFromAxisAngle(Vector3.UnitZ, MathF.PI / 2f);

    // k=4 tread lands at the captured walkable verts when the step origin is
    // (132.0, 77.245, 60.415); step k origin = this + k·(0, 0.5, 0.4), k−4 offset.
    private static readonly Vector3 Step0Origin = new(132.0f, 75.245f, 58.815f);

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

        // Hydrate the step-box collision geometry from the captured dump.
        var dumpPath = Path.Combine(SolutionRoot(), "tests", "AcDream.Core.Tests",
            "Fixtures", "issue185", "0x01000AC5.gfxobj.json");
        Assert.True(File.Exists(dumpPath), $"Missing fixture: {dumpPath}");
        var physics = GfxObjDumpSerializer.Hydrate(GfxObjDumpSerializer.Read(dumpPath));
        cache.RegisterGfxObjForTest(StepGfxObjId, physics);
        float bspR = physics.BoundingSphere?.Radius ?? 1.06f;

        // Stub landblock (terrain far below Z=61) so the outdoor context resolves
        // without the player's grounding ever seeing terrain — it stands on the treads.
        var heights     = new byte[81];
        var heightTable = new float[256];
        for (int i = 0; i < 256; i++) heightTable[i] = -1000f;
        engine.AddLandblock(
            landblockId:  StairLandblock,
            terrain:      new TerrainSurface(heights, heightTable),
            cells:        Array.Empty<CellSurface>(),
            portals:      Array.Empty<PortalPlane>(),
            worldOffsetX: 0f,
            worldOffsetY: 0f);

        for (int k = 0; k < StepCount; k++)
        {
            var origin = Step0Origin + new Vector3(0f, 0.5f * k, 0.4f * k);
            engine.ShadowObjects.Register(
                entityId:      0xF6820100u + (uint)k,
                gfxObjId:      StepGfxObjId,
                worldPos:      origin,
                rotation:      StepRot,
                radius:        bspR,
                worldOffsetX:  0f,
                worldOffsetY:  0f,
                landblockId:   StairLandblock,
                collisionType: ShadowCollisionType.BSP,
                scale:         1.0f,
                seedCellId:    StairCellId);
        }

        return engine;
    }

    private static PhysicsBody GroundedOnTread()
    {
        var tread = new Plane(new Vector3(0f, -0.62469506f, 0.78086877f), 0.765995f);
        return new PhysicsBody
        {
            Position             = new Vector3(131.72375f, 77.49132f, 61.146755f),
            Orientation          = Quaternion.Identity,
            ContactPlaneValid    = true,
            ContactPlane         = tread,
            ContactPlaneCellId   = StairCellId,
            WalkablePolygonValid = true,
            WalkablePlane        = tread,
            WalkableUp           = Vector3.UnitZ,
            WalkableVertices     = new[]
            {
                new Vector3(132.75f, 77.495f, 61.015f),
                new Vector3(131.25f, 77.495f, 61.015f),
                new Vector3(131.25f, 76.995f, 60.615f),
                new Vector3(132.75f, 76.995f, 60.615f),
            },
            TransientState       = TransientStateFlags.Contact | TransientStateFlags.OnWalkable,
        };
    }

    /// <summary>
    /// Drive a held-forward run up the ramp (flat +Y target each tick, physics
    /// climbs Z via contact projection — as the movement controller sends it).
    /// The player must climb PAST the tread seam (Y &gt; 78.1); pre-fix it pins
    /// at ~77.9 and persists a horizontal sliding normal = the wedge.
    /// </summary>
    [Fact]
    public void OutdoorStairs_ForwardRun_ClimbsPastSeam_NoWedge()
    {
        var engine = BuildStairEngine();
        var body   = GroundedOnTread();

        var pos  = body.Position;
        uint cell = StairCellId;
        ResolveResult r = default;

        for (int i = 0; i < 12; i++)
        {
            var target = new Vector3(pos.X, pos.Y + 0.2f, pos.Z);   // flat +Y; physics climbs
            r = engine.ResolveWithTransition(
                currentPos:     pos,
                targetPos:      target,
                cellId:         cell,
                sphereRadius:   0.48f,
                sphereHeight:   1.835f,
                stepUpHeight:   0.6f,
                stepDownHeight: 1.5f,
                isOnGround:     true,
                body:           body,
                moverFlags:     ObjectInfoState.IsPlayer | ObjectInfoState.EdgeSlide,
                movingEntityId: 0x01000000u);

            _out.WriteLine(
                $"f{i}: out=({r.Position.X:F3},{r.Position.Y:F3},{r.Position.Z:F3}) cell=0x{r.CellId:X8} " +
                $"cnV={r.CollisionNormalValid} cn=({r.CollisionNormal.X:F2},{r.CollisionNormal.Y:F2},{r.CollisionNormal.Z:F2}) " +
                $"sliding={body.TransientState.HasFlag(TransientStateFlags.Sliding)} " +
                $"sN=({body.SlidingNormal.X:F2},{body.SlidingNormal.Y:F2},{body.SlidingNormal.Z:F2})");

            pos  = r.Position;
            cell = r.CellId;
            body.Position = pos;
        }

        Assert.True(pos.Y > 78.10f,
            $"Player must climb past the tread seam (reached Y={pos.Y:F3}); pinned at ~77.9 = the " +
            $"#185 fabricated-precipice wedge (PrecipiceSlide horizontal sliding normal absorbs +Y).");
        Assert.False(body.TransientState.HasFlag(TransientStateFlags.Sliding),
            "A continuous walkable ramp seam must not persist a horizontal sliding normal (#137 family).");
    }

    private static string SolutionRoot()
    {
        var dir = AppContext.BaseDirectory;
        while (!string.IsNullOrEmpty(dir))
        {
            if (File.Exists(Path.Combine(dir, "AcDream.slnx")))
                return dir;
            dir = Path.GetDirectoryName(dir);
        }
        throw new InvalidOperationException(
            "Could not locate AcDream.slnx from " + AppContext.BaseDirectory);
    }
}