using System.Numerics;
using AcDream.App.Physics;
using AcDream.Core.Net.Messages;
using AcDream.Core.Physics;
using AcDream.Core.Physics.Motion;
using AcDream.Core.World;
using AcDream.Runtime;
using AcDream.Runtime.Entities;
using AcDream.Runtime.Physics;

namespace AcDream.App.Tests.Physics;

/// <summary>
/// C4 route 4a: behavioural proof that the generic top-of-<c>OnPosition</c>
/// render-pose write no longer double-writes a remote whose accepted Position
/// classifies to
/// <see cref="RuntimeAuthoritativePositionDisposition.NoPositionOperation"/> or
/// <see cref="RuntimeAuthoritativePositionDisposition.Interpolate"/>, and
/// still writes it for every classification route 4a does not own.
///
/// <para>
/// These tests call the PRODUCTION decision-and-mutation entry point
/// (<see cref="LiveEntityNetworkUpdateController.TryApplyGenericRemoteRenderPose"/>)
/// against a real <see cref="WorldEntity"/> and real
/// <see cref="RuntimeAuthoritativePositionRouteClassifier"/> output. Nothing
/// is re-derived in the test body: revert the suppression inside that method
/// and the two suppression tests fail; widen it to <c>route is not null</c>
/// and four of the five legacy-write tests fail (the fifth,
/// <see cref="NoClassificationAtAll_StillTakesTheLegacyRenderPoseWrite"/>,
/// passes a null route and so survives that particular widening — it
/// discriminates the OTHER direction, an over-narrow guard). That is the gap
/// #292 recorded for route 2's source-text pin.
/// </para>
///
/// <para>
/// The suite also pins the ORDERING carve-out
/// (<see cref="LiveEntityNetworkUpdateController.ApplyRemoteContactRouting"/>):
/// an airborne body's contact packet classifies <c>Interpolate</c>, so
/// precedence — not classification — is the only thing keeping a landing
/// creature planting instead of gliding.
/// </para>
/// </summary>
public sealed class LiveEntityNetworkRemoteSteadyStateIntegrationTests
{
    private const uint OldCell = 0x01010001u;
    private const uint WireCell = 0x01010002u;
    private static readonly Vector3 OldPosition = new(5f, 5f, 5f);
    private static readonly Vector3 WirePosition = new(6f, 7f, 8f);

    [Fact]
    public void NoPositionOperation_LeavesTheRenderEntityPoseAndCellUntouched()
    {
        // Retail's airborne no-op (D1): MoveOrTeleport @0x00516330 returns 0
        // for arg4 == 0 and writes nothing. CommittedCellId is nonzero so the
        // cell-less SetPosition branch cannot be what is selected here.
        RuntimeAuthoritativePositionRoute route =
            Classify(hasContact: false, playerDistance: 1f);
        Assert.Equal(
            RuntimeAuthoritativePositionDisposition.NoPositionOperation,
            route.Disposition);

        AssertRenderPoseSuppressed(route);
    }

    [Fact]
    public void Interpolate_LeavesTheRenderEntityPoseAndCellUntouched()
    {
        // Retail's near InterpolateTo queue @0x005163AF. The resolved body,
        // not the raw wire packet, is the branch tail's only writer of the
        // render entity — writing the wire pose here first would be the
        // second writer route 2's original defect consisted of.
        RuntimeAuthoritativePositionRoute route =
            Classify(hasContact: true, playerDistance: 10f);
        Assert.Equal(
            RuntimeAuthoritativePositionDisposition.Interpolate,
            route.Disposition);

        AssertRenderPoseSuppressed(route);
    }

    [Fact]
    public void FarSetPositionSimple_StillTakesTheLegacyRenderPoseWrite()
    {
        RuntimeAuthoritativePositionRoute route =
            Classify(hasContact: true, playerDistance: 200f);
        Assert.Equal(
            RuntimeAuthoritativePositionDisposition.SetPositionSimple,
            route.Disposition);

        AssertRenderPoseWritten(route);
    }

    [Fact]
    public void CellLessRemote_StillTakesTheLegacyRenderPoseWrite()
    {
        RuntimeAuthoritativePositionRoute route = Classify(
            hasContact: false,
            playerDistance: 1f,
            committedCellId: 0u);
        Assert.Equal(
            RuntimeAuthoritativePositionDisposition.SetPosition,
            route.Disposition);

        AssertRenderPoseWritten(route);
    }

    [Fact]
    public void RejectedAuthority_StillTakesTheLegacyRenderPoseWrite()
    {
        RuntimeAuthoritativePositionRoute route = Classify(
            hasContact: true,
            playerDistance: 10f,
            disposition: PositionTimestampDisposition.Rejected);
        Assert.Equal(
            RuntimeAuthoritativePositionDisposition.RejectedAuthority,
            route.Disposition);

        AssertRenderPoseWritten(route);
    }

    [Fact]
    public void RejectedData_StillTakesTheLegacyRenderPoseWrite()
    {
        RuntimeAuthoritativePositionRoute route =
            Classify(hasContact: true, playerDistance: float.NaN);
        Assert.Equal(
            RuntimeAuthoritativePositionDisposition.RejectedData,
            route.Disposition);

        AssertRenderPoseWritten(route);
    }

    [Fact]
    public void NoClassificationAtAll_StillTakesTheLegacyRenderPoseWrite()
    {
        // The login window (no local-player controller yet) and a canonical
        // record that has not claimed a local id both produce a null route.
        // Its doc comment promises the legacy path runs unchanged — so the
        // write must still happen.
        AssertRenderPoseWritten(null);
    }

    // ── Ordering: the airborne snap outranks route 4a's near branch ─────────

    [Fact]
    public void AirborneBodyWithAContactPacket_SnapsInsteadOfEnqueuing()
    {
        // The NPC LANDING packet: the client still believes the body airborne
        // and ACE reports it in contact, close by. That classifies
        // Interpolate — and AP-87's conditions are all benign (0.5 m, sampled,
        // DR-ticked) — so route 4a's branch would ENQUEUE it. It must SNAP:
        // a drudge knocked off a ledge plants, it does not glide to the
        // ground over a packet interval.
        RuntimeAuthoritativePositionRoute route =
            Classify(hasContact: true, playerDistance: 10f);
        Assert.Equal(
            RuntimeAuthoritativePositionDisposition.Interpolate,
            route.Disposition);

        using var fixture = new RemotePlacementDriveFixture();
        (RuntimeEntityRecord record, RemoteMotion remote, _) =
            fixture.AddRemote(0x70005001u, new Vector3(12f, 14f, 7f));
        remote.Body.Position = new Vector3(10f, 10f, 5f);
        // AP-140 (retired 2026-08-04): free flight is retail's CONTACT_TS-clear
        // (`InterpolationManager::adjust_offset` gates on `transient_state & 1`
        // @0x00555D52), not the client `Airborne` walkability flag. Both are
        // stated so the test reads the same before and after that change.
        remote.Airborne = true;
        remote.Body.TransientState = TransientStateFlags.Active;
        var landing = new Vector3(10.5f, 10f, 5f); // 0.5 m — well within 4 m.

        LiveEntityNetworkUpdateController.RemoteContactRouting routing =
            LiveEntityNetworkUpdateController.ApplyRemoteContactRouting(
                fixture.Drive,
                record,
                remote,
                route,
                landing,
                Quaternion.Identity,
                willBeDrTicked: true);

        Assert.Equal(
            LiveEntityNetworkUpdateController.RemoteContactArm.AirborneSnap,
            routing.Arm);
        Assert.Equal(landing, remote.Body.Position);
    }

    [Fact]
    public void GroundedBodyWithANearContactPacket_TakesRoute4asInterpolateBranch()
    {
        // The same packet on a body the client already considers grounded is
        // route 4a's own branch: queued for the per-tick catch-up, body
        // untouched. This is what proves the airborne test above is a
        // PRECEDENCE carve-out and not a blanket disable of route 4a.
        using var fixture = new RemotePlacementDriveFixture();
        (RuntimeEntityRecord record, RemoteMotion remote, _) =
            fixture.AddRemote(0x70005002u, new Vector3(12f, 14f, 7f));
        remote.Body.Position = new Vector3(10f, 10f, 5f);
        remote.Airborne = false;
        var target = new Vector3(10.5f, 10f, 5f);

        LiveEntityNetworkUpdateController.RemoteContactRouting routing =
            LiveEntityNetworkUpdateController.ApplyRemoteContactRouting(
                fixture.Drive,
                record,
                remote,
                Classify(hasContact: true, playerDistance: 10f),
                target,
                Quaternion.Identity,
                willBeDrTicked: true);

        Assert.Equal(
            LiveEntityNetworkUpdateController.RemoteContactArm
                .SteadyStateInterpolate,
            routing.Arm);
        Assert.Equal(new Vector3(10f, 10f, 5f), remote.Body.Position);
    }

    // ── AP-140 (retired 2026-08-04): the gate's predicate is CONTACT ────────

    /// <summary>
    /// The divergence AP-140 recorded, as behaviour. A remote in CONTACT with
    /// a NON-walkable face — sliding down a steep roof — is
    /// <c>Airborne == true</c> by the client flag's own definition
    /// (<c>!Body.OnWalkable</c>), and used to be hard-snapped at
    /// UpdatePosition cadence. Retail interpolates it:
    /// <c>InterpolationManager::adjust_offset</c> @0x00555D30 gates its entire
    /// body on <c>transient_state &amp; 1</c> @0x00555D52, and bit 0 is
    /// <c>CONTACT_TS</c> (acclient.h:3690), not <c>ON_WALKABLE_TS</c> (0x2).
    ///
    /// <para>
    /// This is the ONE state on which the two predicates disagree, so it is
    /// the only test that can discriminate the fix: point the gate back at
    /// <c>remote.Airborne</c> and this test alone fails, with
    /// <c>AirborneSnap</c> and a moved body.
    /// </para>
    /// </summary>
    [Fact]
    public void SteepContactBody_InterpolatesInsteadOfSnapping()
    {
        using var fixture = new RemotePlacementDriveFixture();
        (RuntimeEntityRecord record, RemoteMotion remote, _) =
            fixture.AddRemote(0x70005003u, new Vector3(12f, 14f, 7f));
        var before = new Vector3(10f, 10f, 5f);
        remote.Body.Position = before;
        // Contact with a face too steep to stand on: CONTACT set, ON_WALKABLE
        // clear — exactly what the sweep's SetPositionInternal commit derives
        // on a 52-degree roof since Bug B (204d0ae0) deleted the per-tick
        // walkability forge that used to make this state unreachable.
        remote.Body.TransientState =
            TransientStateFlags.Active | TransientStateFlags.Contact;
        Assert.True(remote.Body.InContact);
        Assert.False(remote.Body.OnWalkable);
        // The client flag agrees with its five writers, all `!Body.OnWalkable`.
        remote.Airborne = !remote.Body.OnWalkable;
        Assert.True(remote.Airborne);

        LiveEntityNetworkUpdateController.RemoteContactRouting routing =
            LiveEntityNetworkUpdateController.ApplyRemoteContactRouting(
                fixture.Drive,
                record,
                remote,
                Classify(hasContact: true, playerDistance: 10f),
                before + new Vector3(0.5f, 0f, 0f),
                Quaternion.Identity,
                willBeDrTicked: true);

        Assert.Equal(
            LiveEntityNetworkUpdateController.RemoteContactArm
                .SteadyStateInterpolate,
            routing.Arm);
        // The interpolate arm enqueues a waypoint and leaves the body to the
        // per-tick catch-up; the snap arm would have written it directly.
        Assert.Equal(before, remote.Body.Position);
    }

    /// <summary>
    /// The regression guard on the other side of the same gate: a genuinely
    /// free-flying remote — no contact with anything — must still take the
    /// hard snap. Retail's <c>adjust_offset</c> writes nothing at all with
    /// <c>CONTACT_TS</c> clear, so the queued waypoint cannot advance the
    /// body and the authoritative position is the only thing that can.
    /// Widen the gate to "always interpolate" and this test fails.
    /// </summary>
    [Fact]
    public void FreeFlightBodyWithNoContact_StillSnaps()
    {
        using var fixture = new RemotePlacementDriveFixture();
        (RuntimeEntityRecord record, RemoteMotion remote, _) =
            fixture.AddRemote(0x70005004u, new Vector3(12f, 14f, 7f));
        remote.Body.Position = new Vector3(10f, 10f, 5f);
        remote.Body.TransientState = TransientStateFlags.Active;
        Assert.False(remote.Body.InContact);
        remote.Airborne = !remote.Body.OnWalkable;
        var landing = new Vector3(10.5f, 10f, 5f);

        LiveEntityNetworkUpdateController.RemoteContactRouting routing =
            LiveEntityNetworkUpdateController.ApplyRemoteContactRouting(
                fixture.Drive,
                record,
                remote,
                Classify(hasContact: true, playerDistance: 10f),
                landing,
                Quaternion.Identity,
                willBeDrTicked: true);

        Assert.Equal(
            LiveEntityNetworkUpdateController.RemoteContactArm.AirborneSnap,
            routing.Arm);
        Assert.Equal(landing, remote.Body.Position);
    }

    /// <summary>
    /// The unchanged third state: contact with WALKABLE ground. Both
    /// predicates agree here, and both before and after AP-140's fix the
    /// packet interpolates. Pinned so a future edit cannot "simplify" the
    /// gate into something that only satisfies the two tests above.
    /// </summary>
    [Fact]
    public void WalkableGroundedBody_IsUnchangedAndStillInterpolates()
    {
        using var fixture = new RemotePlacementDriveFixture();
        (RuntimeEntityRecord record, RemoteMotion remote, _) =
            fixture.AddRemote(0x70005005u, new Vector3(12f, 14f, 7f));
        var before = new Vector3(10f, 10f, 5f);
        remote.Body.Position = before;
        remote.Body.TransientState = TransientStateFlags.Active
            | TransientStateFlags.Contact
            | TransientStateFlags.OnWalkable;
        remote.Airborne = !remote.Body.OnWalkable;
        Assert.False(remote.Airborne);

        LiveEntityNetworkUpdateController.RemoteContactRouting routing =
            LiveEntityNetworkUpdateController.ApplyRemoteContactRouting(
                fixture.Drive,
                record,
                remote,
                Classify(hasContact: true, playerDistance: 10f),
                before + new Vector3(0.5f, 0f, 0f),
                Quaternion.Identity,
                willBeDrTicked: true);

        Assert.Equal(
            LiveEntityNetworkUpdateController.RemoteContactArm
                .SteadyStateInterpolate,
            routing.Arm);
        Assert.Equal(before, remote.Body.Position);
    }

    private static void AssertRenderPoseSuppressed(
        RuntimeAuthoritativePositionRoute? route)
    {
        WorldEntity entity = MakeEntity();
        var beforeRotation = entity.Rotation;

        bool written = LiveEntityNetworkUpdateController
            .TryApplyGenericRemoteRenderPose(
                entity,
                route,
                WirePosition,
                WireCell,
                Quaternion.CreateFromAxisAngle(Vector3.UnitZ, 1.1f));

        Assert.False(written);
        Assert.Equal(OldPosition, entity.Position);
        Assert.Equal(OldCell, entity.ParentCellId);
        Assert.Equal(beforeRotation, entity.Rotation);
    }

    private static void AssertRenderPoseWritten(
        RuntimeAuthoritativePositionRoute? route)
    {
        WorldEntity entity = MakeEntity();
        var wireRotation = Quaternion.CreateFromAxisAngle(Vector3.UnitZ, 1.1f);

        bool written = LiveEntityNetworkUpdateController
            .TryApplyGenericRemoteRenderPose(
                entity,
                route,
                WirePosition,
                WireCell,
                wireRotation);

        Assert.True(written);
        Assert.Equal(WirePosition, entity.Position);
        Assert.Equal(WireCell, entity.ParentCellId);
        Assert.Equal(wireRotation, entity.Rotation);
    }

    private static WorldEntity MakeEntity() => new()
    {
        Id = 1u,
        SourceGfxObjOrSetupId = 1u,
        Position = OldPosition,
        Rotation = Quaternion.Identity,
        MeshRefs = Array.Empty<MeshRef>(),
        ParentCellId = OldCell,
    };

    private const uint Cell = 0x0101FFFFu;

    private static RuntimeAuthoritativePositionRoute Classify(
        bool hasContact,
        float playerDistance,
        uint committedCellId = OldCell,
        PositionTimestampDisposition disposition =
            PositionTimestampDisposition.Apply) =>
        RuntimeAuthoritativePositionRouteClassifier.ClassifyAcceptedPosition(
            new RuntimeAcceptedPositionRouteRequest(
                new RuntimeAuthoritativePositionAuthority(
                    new RuntimeGenerationToken(7),
                    new RuntimeEntityKey(0x70000001u, 3),
                    PositionAuthorityVersion: 11UL,
                    AcceptedPositionSequence: 20,
                    PreviousTeleportSequence: 10,
                    AcceptedTeleportSequence: 10,
                    disposition),
                RuntimePositionEntityKind.Remote,
                RuntimeAcceptedPositionSource.PositionEvent,
                new CreateObject.ServerPosition(
                    Cell, 10f, 20f, 30f, 1f, 0f, 0f, 0f),
                PlacementFrame: 0u,
                PositionPackVelocity: Vector3.Zero,
                committedCellId,
                hasContact,
                playerDistance,
                UsePositionFromServer: false,
                HasAnimations: false,
                default));
}