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>
/// Campaign P Slice P3 item 4 (#165): diagnosis-only fixtures discriminating
/// the three candidate mechanisms the research doc
/// (<c>docs/research/2026-07-29-remote-and-world-specials-pseudocode.md</c>
/// §2.4) lists for "remote entities penetrate walls before stopping":
/// <list type="bullet">
///   <item>(a) the <c>InterpolationManager</c> unclamped stall-fail "tail
///     delta" snap (<c>node_fail_counter &gt; 3</c>) commits a position on
///     the far side of / inside a wall in one tick, and the SAME tick's
///     <c>ResolveWithTransition</c> sweep fails to catch the crossing for a
///     large single-tick delta;</item>
///   <item>(b) a one-frame skip of the sweep entirely
///     (<c>RuntimeRemotePhysicsUpdater.cs</c> gates the whole resolve on
///     <c>rm.CellId != 0 &amp;&amp; LandblockCount &gt; 0</c>) reachable on
///     some tick other than first-spawn;</item>
///   <item>(c) render/interpolation presentation lag on the App side —
///     out of Core/Runtime scope, not addressed here.</item>
/// </list>
///
/// <para>
/// No live client, no dat dependency — every fixture here is synthetic
/// geometry driven directly through <see cref="PhysicsEngine.ResolveWithTransition"/>,
/// matching the existing <see cref="SphereCollisionFamilyTests"/> /
/// <see cref="Issue182CrowdJumpTests"/> pattern.
/// </para>
/// </summary>
public class Issue165RemoteWallPenetrationDiagnosticTests
{
    private readonly ITestOutputHelper _out;
    public Issue165RemoteWallPenetrationDiagnosticTests(ITestOutputHelper output) => _out = output;

    private const uint TestLandblockId = 0xA9D60000u;
    private const uint TestCellId = TestLandblockId | 0x0001u;

    private const float SphereRadius = 0.48f;
    private const float SphereHeight = 1.835f;
    private const float StepUpHeight = 0.4f;
    private const float StepDownHeight = 0.4f;

    /// <summary>
    /// Candidate (a) discriminator: mirrors
    /// <see cref="SphereCollisionFamilyTests.GroundedSingleCreature_HeadOnPush_BlocksWithoutPenetration"/>
    /// (30 small 0.08 m steps reaching a creature sphere at Y=11.5, surface
    /// contact Y≈10.54) but replaces the 30-tick approach with ONE resolve
    /// call spanning the ENTIRE distance in a single tick — exactly what an
    /// <c>InterpolationManager</c> unclamped tail-delta snap (the full
    /// remaining distance to the queue's tail node, no speed cap) would hand
    /// <c>ResolveWithTransition</c> as its <c>targetPos</c> argument.
    /// </summary>
    [Fact]
    public void SingleLargeTickJumpThroughObstacle_IsStillBlockedAtSurface()
    {
        var engine = BuildEngine();
        RegisterCreatureSphere(engine, 0xC0F0u, 12f, 11.5f); // due north, same as the proven 30-tick test

        var body = MakeGroundedBody(new Vector3(12f, 10f, 0f));
        // ONE resolve call for the full 2.4 m the 30-tick test covers in
        // 0.08 m increments — simulating an unclamped stall-fail snap that
        // jumps the remote directly toward (and past) the target node in a
        // single tick, rather than a smoothly interpolated approach.
        Vector3 farTarget = new(12f, 12.4f, 0f);

        var result = engine.ResolveWithTransition(
            body.Position, farTarget, TestCellId,
            SphereRadius, SphereHeight, StepUpHeight, StepDownHeight,
            isOnGround: true, body: body,
            moverFlags: ObjectInfoState.EdgeSlide,
            movingEntityId: 0);

        _out.WriteLine(
            $"single-jump result pos=({result.Position.X:F3},{result.Position.Y:F3},{result.Position.Z:F3}) "
            + $"ok={result.Ok} collisionNormalValid={result.CollisionNormalValid}");

        // If the sweep correctly handles a large single-tick delta, the
        // result is IDENTICAL in kind to the proven 30-tick test: blocked at
        // the sphere surface (Y≈10.54), never past Y=11.02 (the near edge of
        // the creature sphere itself, combinedR=0.96 short of full
        // interpenetration) — NOT at or past the creature's own center
        // (Y=11.5), which would mean the sweep missed the crossing entirely.
        Assert.True(
            result.Position.Y < 10.7f,
            "A single large-tick jump through solid geometry must be blocked "
            + $"at the surface, matching the small-step case; got Y={result.Position.Y:F3}. "
            + "If this fails, candidate (a) (the sweep does not catch large "
            + "single-tick deltas) is CONFIRMED as a contributing #165 mechanism.");
    }

    /// <summary>
    /// Control for the test above: the SAME single large jump, but with NO
    /// obstacle registered — confirms the mover actually reaches the far
    /// target when nothing blocks it (proving the previous test's block is
    /// really the obstacle, not some unrelated large-distance resolve
    /// failure/clamp).
    /// </summary>
    [Fact]
    public void SingleLargeTickJumpWithNoObstacle_ReachesFarTarget()
    {
        var engine = BuildEngine();

        var body = MakeGroundedBody(new Vector3(12f, 10f, 0f));
        Vector3 farTarget = new(12f, 12.4f, 0f);

        var result = engine.ResolveWithTransition(
            body.Position, farTarget, TestCellId,
            SphereRadius, SphereHeight, StepUpHeight, StepDownHeight,
            isOnGround: true, body: body,
            moverFlags: ObjectInfoState.EdgeSlide,
            movingEntityId: 0);

        _out.WriteLine($"unobstructed pos=({result.Position.X:F3},{result.Position.Y:F3})");

        Assert.True(
            result.Position.Y > 12.2f,
            $"An unobstructed large single-tick jump must actually complete; got Y={result.Position.Y:F3}");
    }

    /// <summary>
    /// Candidate (a), sharper variant: the unclamped snap can also land the
    /// PRE-INTEGRATE start point already past/inside the obstacle in a
    /// pathological case (e.g. two consecutive stalled ticks). Confirms the
    /// sweep also rejects a targetPos that starts ALREADY behind the
    /// obstacle's near surface relative to the swept segment — i.e. even a
    /// start point inside the creature's overlap zone resolves to a valid,
    /// non-penetrating position rather than silently accepting the
    /// already-tunneled candidate.
    /// </summary>
    [Fact]
    public void SingleLargeTickJumpStartingInsideObstacleOverlap_DoesNotAcceptTunneledCandidate()
    {
        var engine = BuildEngine();
        RegisterCreatureSphere(engine, 0xC0F1u, 12f, 11.5f);

        // Start already 0.3 m PAST the surface contact point (Y=10.84,
        // inside the combined-radius overlap zone starting at Y≈10.54) —
        // simulating a start position an earlier unclamped snap already
        // over-shot into.
        var body = MakeGroundedBody(new Vector3(12f, 10.84f, 0f));
        Vector3 farTarget = new(12f, 13f, 0f);

        var result = engine.ResolveWithTransition(
            body.Position, farTarget, TestCellId,
            SphereRadius, SphereHeight, StepUpHeight, StepDownHeight,
            isOnGround: true, body: body,
            moverFlags: ObjectInfoState.EdgeSlide,
            movingEntityId: 0);

        _out.WriteLine(
            $"overlap-start result pos=({result.Position.X:F3},{result.Position.Y:F3}) "
            + $"input Y=10.84 (already inside the {0.48f + 0.48f:F2} m combined-radius overlap)");

        // Retail's own validate_transition restores curr_pos on a non-clean
        // step when starting deep inside overlapping spheres (per the
        // physics digest's #184 DO-NOT-RETRY note) — this is NOT a bug to
        // chase if the position stays pinned near the start rather than
        // sailing through to the far target.
        Assert.True(
            result.Position.Y < 11.4f,
            "A candidate that starts inside a solid obstacle's overlap zone must not "
            + $"sail through to the far target; got Y={result.Position.Y:F3}");
    }

    private static PhysicsEngine BuildEngine()
    {
        var 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;
    }

    private static void RegisterCreatureSphere(
        PhysicsEngine engine, uint entityId, float x, float y)
    {
        engine.ShadowObjects.Register(
            entityId, gfxObjId: 0u,
            new Vector3(x, y, SphereRadius), Quaternion.Identity, SphereRadius,
            worldOffsetX: 0f, worldOffsetY: 0f, landblockId: TestLandblockId,
            collisionType: ShadowCollisionType.Sphere,
            cylHeight: 0f, scale: 1f,
            state: 0u,
            flags: EntityCollisionFlags.IsCreature,
            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,
        };
    }
}