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

namespace AcDream.Runtime.Tests.Physics;

/// <summary>
/// C4 route 4a: focused tests for the Runtime-owned decision that replaces
/// the two independent per-kind (player-remote / NPC-remote) copies that
/// used to live in <c>LiveEntityNetworkUpdateController</c>. Each test below
/// was verified to actually discriminate its own fix by temporarily
/// reverting the corresponding condition in
/// <see cref="RuntimeRemoteSteadyStatePosition"/> and confirming the
/// matching test failed, then restoring it — see the route 4a implementation
/// report for the revert/restore log.
/// </summary>
public sealed class RuntimeRemoteSteadyStatePositionTests
{
    private const uint Cell = 0x0101FFFFu;

    /// <summary>A remote that has already received at least one server
    /// sample, so AP-87's <c>firstUp</c> hint is false and the other two
    /// conditions are the ones under test.</summary>
    private static RemoteMotion MakeSampledRemote(Vector3 bodyPosition)
    {
        var remote = new RemoteMotion();
        remote.Body.Position = bodyPosition;
        remote.Body.Orientation = Quaternion.Identity;
        remote.LastServerPosTime = 1_700_000_000d;
        return remote;
    }

    private static (RemoteMotion Remote, EntityPhysicsHost Host) MakeRemoteWithHost(
        Vector3 bodyPosition)
    {
        RemoteMotion remote = MakeSampledRemote(bodyPosition);
        EntityPhysicsHost host = new(
            id: 0x70000001u,
            getPosition: () => new Position(0x0001u, remote.Body.Position, remote.Body.Orientation),
            getVelocity: () => remote.Body.Velocity,
            getRadius: () => 0.48f,
            inContact: () => remote.Body.InContact,
            minterpMaxSpeed: () => null,
            curTime: () => 0d,
            physicsTimerTime: () => 0d,
            getObjectA: _ => null,
            handleUpdateTarget: _ => { },
            interruptCurrentMovement: () => { });
        remote.BindCanonicalRuntime(
            () => host,
            () => 0x0001u,
            _ => { });
        remote.MarkFullPhysicsHostBound();
        return (remote, host);
    }

    // ── AP-87 (register row, carried forward) ──────────────────────────────

    [Fact]
    public void ApplyInterpolate_BodyFarFromTarget_SnapsRatherThanEnqueues()
    {
        // AP-87's load-bearing condition: |Body.Position - worldPos| > 4 m.
        // An unplaced body (spawn-seed origin) must SNAP, never enqueue —
        // enqueuing here is exactly the #184 invisible-but-solid regression
        // this backstop exists to prevent.
        RemoteMotion remote = MakeSampledRemote(new Vector3(0f, 0f, 0f));
        var target = new Vector3(50f, 0f, 0f); // 50 m away — far beyond 4 m.

        RuntimeRemoteSteadyStatePosition.Action action =
            RuntimeRemoteSteadyStatePosition.ApplyInterpolate(
                remote,
                target,
                Quaternion.Identity,
                isMovingTo: false,
                willBeDrTicked: true);

        Assert.Equal(RuntimeRemoteSteadyStatePosition.Action.Snapped, action);
        Assert.Equal(target, remote.Body.Position);
    }

    [Fact]
    public void ApplyInterpolate_NotDrTicked_SnapsEvenWhenClose()
    {
        // AP-87's second condition: !willBeDrTicked. A body with no consumer
        // to walk the queue must snap even for a 1 m correction, or it never
        // reaches the target at all.
        RemoteMotion remote = MakeSampledRemote(new Vector3(10f, 10f, 5f));
        var target = new Vector3(10.5f, 10f, 5f); // 0.5 m — well within 4 m.

        RuntimeRemoteSteadyStatePosition.Action action =
            RuntimeRemoteSteadyStatePosition.ApplyInterpolate(
                remote,
                target,
                Quaternion.Identity,
                isMovingTo: false,
                willBeDrTicked: false);

        Assert.Equal(RuntimeRemoteSteadyStatePosition.Action.Snapped, action);
        Assert.Equal(target, remote.Body.Position);
    }

    [Fact]
    public void ApplyInterpolate_FirstUpBeforeAnyServerSample_Snaps()
    {
        // AP-87's third condition, carried forward from the NPC copy rather
        // than silently dropped: a remote that has never been stamped with a
        // server sample snaps even when both other conditions are benign.
        // Structurally unreachable for player remotes, whose caller stamps
        // LastServerPosTime before it routes — which is exactly why keeping
        // it costs the player arm nothing.
        var remote = new RemoteMotion();
        remote.Body.Position = new Vector3(10f, 10f, 5f);
        remote.Body.Orientation = Quaternion.Identity;
        Assert.Equal(0d, remote.LastServerPosTime);
        var target = new Vector3(10.5f, 10f, 5f);

        RuntimeRemoteSteadyStatePosition.Action action =
            RuntimeRemoteSteadyStatePosition.ApplyInterpolate(
                remote,
                target,
                Quaternion.Identity,
                isMovingTo: false,
                willBeDrTicked: true);

        Assert.Equal(RuntimeRemoteSteadyStatePosition.Action.Snapped, action);
        Assert.Equal(target, remote.Body.Position);
    }

    [Fact]
    public void ApplyInterpolate_NearAndDrTicked_EnqueuesWithoutTouchingBodyPosition()
    {
        // The ordinary retail near case: no AP-87 condition holds, so the
        // body is queued for the per-tick catch-up, not hard-snapped.
        RemoteMotion remote = MakeSampledRemote(new Vector3(10f, 10f, 5f));
        var target = new Vector3(10.5f, 10f, 5f);

        RuntimeRemoteSteadyStatePosition.Action action =
            RuntimeRemoteSteadyStatePosition.ApplyInterpolate(
                remote,
                target,
                Quaternion.Identity,
                isMovingTo: false,
                willBeDrTicked: true);

        Assert.Equal(RuntimeRemoteSteadyStatePosition.Action.Enqueued, action);
        // The body itself is not hard-moved by the enqueue path — the
        // per-tick InterpolationManager/adjust_offset chain walks it there.
        Assert.Equal(new Vector3(10f, 10f, 5f), remote.Body.Position);
    }

    /// <summary>
    /// TS-44 stays an NPC-only CALLER gate: the seam itself is the
    /// kind-agnostic retail decision, so a sticky-armed host does NOT change
    /// what it does. Folding the sticky check in here would have silently
    /// extended TS-44 to player remotes, which have never had one.
    /// </summary>
    [Fact]
    public void ApplyInterpolate_IsIndifferentToTheStickyLease()
    {
        (RemoteMotion remote, EntityPhysicsHost host) = MakeRemoteWithHost(
            new Vector3(0f, 0f, 0f));
        host.PositionManager.StickTo(objectId: 0x70000002u, radius: 1f, height: 1f);
        Assert.NotEqual(0u, host.PositionManager.GetStickyObjectId());

        RuntimeRemoteSteadyStatePosition.Action action =
            RuntimeRemoteSteadyStatePosition.ApplyInterpolate(
                remote,
                new Vector3(50f, 0f, 0f),
                Quaternion.Identity,
                isMovingTo: false,
                willBeDrTicked: true);

        Assert.Equal(RuntimeRemoteSteadyStatePosition.Action.Snapped, action);
    }

    // ── Per-entity currency ─────────────────────────────────────────────────
    // Contract item 4: N remotes, no shared pending slot — unlike route 2's
    // single-slot RuntimeAcceptedPositionDriveController, this decision
    // carries no state of its own between calls. Two remotes classified in
    // the same tick must not observe or mutate each other.

    [Fact]
    public void TwoRemotesInTheSameTick_ApplyIndependentlyWithNoCrossContamination()
    {
        RemoteMotion farRemote = MakeSampledRemote(new Vector3(0f, 0f, 0f)); // will snap.
        RemoteMotion nearRemote = MakeSampledRemote(new Vector3(10f, 10f, 5f)); // will enqueue.

        RuntimeRemoteSteadyStatePosition.Action farAction =
            RuntimeRemoteSteadyStatePosition.ApplyInterpolate(
                farRemote,
                new Vector3(50f, 0f, 0f),
                Quaternion.Identity,
                isMovingTo: false,
                willBeDrTicked: true);
        RuntimeRemoteSteadyStatePosition.Action nearAction =
            RuntimeRemoteSteadyStatePosition.ApplyInterpolate(
                nearRemote,
                new Vector3(10.5f, 10f, 5f),
                Quaternion.Identity,
                isMovingTo: false,
                willBeDrTicked: true);

        Assert.Equal(RuntimeRemoteSteadyStatePosition.Action.Snapped, farAction);
        Assert.Equal(RuntimeRemoteSteadyStatePosition.Action.Enqueued, nearAction);
        Assert.Equal(new Vector3(50f, 0f, 0f), farRemote.Body.Position);
        // nearRemote's body is untouched by farRemote's snap — no shared state.
        Assert.Equal(new Vector3(10f, 10f, 5f), nearRemote.Body.Position);
    }

    // ── Ownership: exactly two dispositions, everything else falls through ──

    [Fact]
    public void OwnsSteadyState_IsTrueForExactlyTheTwoNoPlacementDispositions()
    {
        Assert.True(RuntimeRemoteSteadyStatePosition.OwnsSteadyState(
            Classify(hasContact: false, playerDistance: 1f)));
        Assert.True(RuntimeRemoteSteadyStatePosition.OwnsSteadyState(
            Classify(hasContact: true, playerDistance: 10f)));
    }

    [Theory]
    // Far (>=96 m) — SetPositionSimple, route 4b.
    [InlineData(true, 200f, Cell, 10, 10, PositionTimestampDisposition.Apply)]
    // Cell-less canonical body — SetPosition, route 4b.
    [InlineData(true, 10f, 0u, 10, 10, PositionTimestampDisposition.Apply)]
    // Fresh TELEPORT_TS — SetPosition, route 4b.
    [InlineData(true, 10f, Cell, 10, 11, PositionTimestampDisposition.Apply)]
    // Rejected admission — RejectedAuthority.
    [InlineData(true, 10f, Cell, 10, 10, PositionTimestampDisposition.Rejected)]
    // Nonfinite derived distance — RejectedData.
    [InlineData(true, float.NaN, Cell, 10, 10, PositionTimestampDisposition.Apply)]
    public void OwnsSteadyState_IsFalseForEveryOtherClassification(
        bool hasContact,
        float playerDistance,
        uint committedCellId,
        ushort previousTeleport,
        ushort acceptedTeleport,
        PositionTimestampDisposition disposition)
    {
        RuntimeAuthoritativePositionRoute route = Classify(
            hasContact,
            playerDistance,
            committedCellId,
            previousTeleport,
            acceptedTeleport,
            disposition);

        Assert.NotEqual(
            RuntimeAuthoritativePositionDisposition.Interpolate,
            route.Disposition);
        Assert.NotEqual(
            RuntimeAuthoritativePositionDisposition.NoPositionOperation,
            route.Disposition);
        Assert.False(RuntimeRemoteSteadyStatePosition.OwnsSteadyState(route));
    }

    [Fact]
    public void OwnsSteadyState_IsFalseWhenNothingWasClassified()
    {
        // A null route is "route 4a has no opinion" — the legacy path runs
        // completely unchanged, exactly as its doc comment claims.
        Assert.False(RuntimeRemoteSteadyStatePosition.OwnsSteadyState(null));
        Assert.False(RuntimeRemoteSteadyStatePosition.IsAirborneNoOperation(null));
        Assert.False(RuntimeRemoteSteadyStatePosition.IsNearInterpolate(null));
    }

    // ── D2: ConstrainTo timing/anchor ───────────────────────────────────────

    [Fact]
    public void ArmConstraintAfterOperation_AnchorsToTheHostsCurrentLivePosition()
    {
        (RemoteMotion remote, EntityPhysicsHost host) = MakeRemoteWithHost(
            new Vector3(1f, 2f, 3f));

        // Simulate the operation having already moved the body (a Snapped
        // outcome) BEFORE ConstrainTo arms — D2 requires the anchor to read
        // the POST-move position, never the pre-move one.
        remote.Body.Position = new Vector3(9f, 9f, 9f);

        RuntimeRemoteSteadyStatePosition.ArmConstraintAfterOperation(host);

        ConstraintManager? constraint = host.PositionManager.Constraint;
        Assert.NotNull(constraint);
        Assert.True(constraint!.IsConstrained);
        Assert.Equal(new Vector3(9f, 9f, 9f), constraint.ConstraintPos.Frame.Origin);
        // Anchored to itself at arm time -> zero initial offset, matching
        // retail's per-packet re-anchor.
        Assert.Equal(0f, constraint.ConstraintPosOffset, 3);
    }

    [Fact]
    public void TryArmConstraintAfterOperation_ArmsForTheNearInterpolateBranch()
    {
        (RemoteMotion remote, EntityPhysicsHost host) = MakeRemoteWithHost(
            new Vector3(1f, 2f, 3f));

        Assert.True(RuntimeRemoteSteadyStatePosition.TryArmConstraintAfterOperation(
            Classify(hasContact: true, playerDistance: 10f),
            remote));
        Assert.True(host.PositionManager.Constraint?.IsConstrained);
    }

    [Fact]
    public void TryArmConstraintAfterOperation_SkipsTheAirborneNoOperation()
    {
        // MoveOrTeleport returns 0 for arg4 == 0, so HandleReceivedPosition's
        // `if (MoveOrTeleport(...) != 0)` never reaches ConstrainTo.
        (RemoteMotion remote, EntityPhysicsHost host) = MakeRemoteWithHost(
            new Vector3(1f, 2f, 3f));

        Assert.False(RuntimeRemoteSteadyStatePosition.TryArmConstraintAfterOperation(
            Classify(hasContact: false, playerDistance: 10f),
            remote));
        Assert.Null(host.PositionManager.Constraint);
    }

    /// <summary>
    /// C4 route 4b-2: the far branch moved onto the post-operation arm with
    /// route 4a's two. Retail's `MoveOrTeleport` returns 1 @0x005163E8 there,
    /// so `HandleReceivedPosition`'s single `ConstrainTo` @0x00454272 runs —
    /// and the App's legacy PRE-operation call site now reads the same
    /// predicate and skips it, so it is armed exactly once.
    /// </summary>
    [Fact]
    public void TryArmConstraintAfterOperation_ArmsForTheFarSnapBranch()
    {
        (RemoteMotion remote, EntityPhysicsHost host) = MakeRemoteWithHost(
            new Vector3(1f, 2f, 3f));

        RuntimeAuthoritativePositionRoute far =
            Classify(hasContact: true, playerDistance: 200f);
        Assert.Equal(
            RuntimeAuthoritativePositionDisposition.SetPositionSimple,
            far.Disposition);

        Assert.True(RuntimeRemoteSteadyStatePosition.TryArmConstraintAfterOperation(
            far,
            remote));
        Assert.True(host.PositionManager.Constraint?.IsConstrained);
    }

    [Fact]
    public void TryArmConstraintAfterOperation_SkipsClassificationsNoArmOwns()
    {
        // The cell-less half, the two rejections, and "no classification at
        // all" still arm their leash through the untouched legacy
        // PRE-operation call site, not through here. Arming here too would
        // double-arm them.
        (RemoteMotion remote, EntityPhysicsHost host) = MakeRemoteWithHost(
            new Vector3(1f, 2f, 3f));

        Assert.False(RuntimeRemoteSteadyStatePosition.TryArmConstraintAfterOperation(
            Classify(hasContact: true, playerDistance: 10f, committedCellId: 0u),
            remote));
        Assert.False(RuntimeRemoteSteadyStatePosition.TryArmConstraintAfterOperation(
            Classify(
                hasContact: true,
                playerDistance: 10f,
                disposition: PositionTimestampDisposition.Rejected),
            remote));
        Assert.False(RuntimeRemoteSteadyStatePosition.TryArmConstraintAfterOperation(
            Classify(hasContact: true, playerDistance: float.NaN),
            remote));
        Assert.False(RuntimeRemoteSteadyStatePosition.TryArmConstraintAfterOperation(
            null,
            remote));
        Assert.Null(host.PositionManager.Constraint);
    }

    private static RuntimeAuthoritativePositionRoute Classify(
        bool hasContact,
        float playerDistance,
        uint committedCellId = Cell,
        ushort previousTeleport = 10,
        ushort acceptedTeleport = 10,
        PositionTimestampDisposition disposition =
            PositionTimestampDisposition.Apply) =>
        RuntimeAuthoritativePositionRouteClassifier.ClassifyAcceptedPosition(
            new RuntimeAcceptedPositionRouteRequest(
                new RuntimeAuthoritativePositionAuthority(
                    new RuntimeGenerationToken(7),
                    new RuntimeEntityKey(0x70000001u, 3),
                    PositionAuthorityVersion: 11UL,
                    AcceptedPositionSequence: 20,
                    previousTeleport,
                    acceptedTeleport,
                    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));
}