using System.Buffers.Binary;
using System.Collections.Immutable;
using System.Net;
using System.Numerics;
using System.Reflection;
using AcDream.Core.Net;
using AcDream.Core.Net.Messages;
using AcDream.Core.Physics;
using AcDream.Headless.Configuration;
using AcDream.Headless.Credentials;
using AcDream.Headless.Diagnostics;
using AcDream.Headless.Hosting;
using AcDream.Headless.Platform;
using AcDream.Runtime;
using AcDream.Runtime.Entities;
using AcDream.Runtime.Gameplay;
using AcDream.Runtime.Physics;
using AcDream.Runtime.Session;
using AcDream.Runtime.World;

namespace AcDream.Headless.Tests;

public sealed class HeadlessSessionHostTests
{
    [Fact]
    public void SingleSessionStartsReconnectsAndConvergesWithoutPresentation()
    {
        var operations = new FixtureSessionOperations();
        using var diagnosticsOutput = new StringWriter();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(diagnosticsOutput),
            operations);

        RuntimeSessionStartResult first = host.Start();
        ulong firstGeneration = host.Runtime.Generation.Value;
        host.Tick(0.015d);
        RuntimeSessionStartResult second = host.Reconnect();

        Assert.Equal(RuntimeSessionStartStatus.Connected, first.Status);
        Assert.Equal(RuntimeSessionStartStatus.Connected, second.Status);
        Assert.Equal(0x50000002u, first.CharacterId);
        Assert.Equal("Headless", host.ActiveCharacterName);
        Assert.True(host.Runtime.Session.IsInWorld);
        Assert.True(host.Runtime.Generation.Value > firstGeneration);
        Assert.Equal(2, operations.CreatedSessionCount);
        Assert.Equal(1, operations.DisposedSessionCount);

        host.Dispose();

        Assert.Equal(2, operations.DisposedSessionCount);
        Assert.True(host.Runtime.CaptureOwnership().IsConverged);
        Assert.True(credential.IsDisposed);
        string diagnostics = diagnosticsOutput.ToString();
        Assert.Contains("\"state\":\"start-result\"", diagnostics);
        Assert.DoesNotContain("password", diagnostics);
        Assert.DoesNotContain("AcDream.App", diagnostics);
    }

    [Fact]
    public async Task ProcessHostRunsUntilCancellationAndReturnsStableExitCode()
    {
        var configuration = new HeadlessConfiguration
        {
            Version = 1,
            Sessions =
            [
                Descriptor(
                    HeadlessCredentialProviderKind.StandardInput,
                    "stdin-bot"),
            ],
        };
        HeadlessPathSet paths = HeadlessPathSet.Resolve(
            new HeadlessPathOverrides());
        using var diagnostics = new StringWriter();
        var operations = new FixtureSessionOperations();
        using var host = new HeadlessProcessHost(
            configuration,
            paths,
            new System.IO.StringReader(
                "process-password" + Environment.NewLine),
            diagnostics,
            operations);
        using var cancellation = new CancellationTokenSource();
        cancellation.Cancel();

        HeadlessExitCode result =
            await host.RunAsync(cancellation.Token);

        Assert.Equal(HeadlessExitCode.Success, result);
        Assert.True(host.Session.Runtime.Session.IsInWorld);
        Assert.DoesNotContain(
            "process-password",
            diagnostics.ToString());
    }

    [Fact]
    public async Task DirectCredentialsOverrideSingleConfiguredSession()
    {
        var configuration = new HeadlessConfiguration
        {
            Version = 1,
            Sessions = [Descriptor()],
        };
        HeadlessPathSet paths = HeadlessPathSet.Resolve(
            new HeadlessPathOverrides());
        using var diagnostics = new StringWriter();
        var operations = new FixtureSessionOperations();
        using var host = new HeadlessProcessHost(
            configuration,
            paths,
            TextReader.Null,
            diagnostics,
            operations,
            directCredentials: new HeadlessDirectCredentials(
                "direct-account",
                "direct-secret"));
        using var cancellation = new CancellationTokenSource();
        cancellation.Cancel();

        HeadlessExitCode result =
            await host.RunAsync(cancellation.Token);

        Assert.Equal(HeadlessExitCode.Success, result);
        Assert.Equal("direct-account", operations.LastUser);
        Assert.Equal("direct-secret", operations.LastPassword);
        Assert.DoesNotContain(
            "direct-secret",
            diagnostics.ToString());
    }

    [Fact]
    public void DirectFrameUsesSharedRetailOrderAndMovementCadence()
    {
        var operations = new FixtureSessionOperations();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        using var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(TextWriter.Null),
            operations);
        Assert.Equal(
            RuntimeSessionStartStatus.Connected,
            host.Start().Status);
        HydrateGroundedPlayer(host.Runtime);
        var sent = new List<(byte[] Body, double Time)>();
        var trace = new RuntimeTraceRecorder();
        using IDisposable subscription =
            host.Runtime.Subscribe(trace);
        operations.Sessions[^1].GameActionCapture =
            body => sent.Add((
                body,
                host.Runtime.Clock.SimulationTimeSeconds));

        RuntimeCommandResult intent = host.Commands.Movement.SetIntent(
            host.Runtime.Generation,
            new MovementInput(Forward: true, Run: true));
        host.Tick(0.015d);

        Assert.True(intent.Accepted);
        Assert.Contains(
            trace.Entries,
            static entry =>
                entry.Kind == RuntimeTraceKind.Movement);
        Assert.Equal(
            [
                MoveToState.MoveToStateAction,
                AutonomousPosition.AutonomousPositionAction,
            ],
            sent.Select(static entry =>
                ActionOpcode(entry.Body)).ToArray());

        sent.Clear();
        for (int index = 0; index < 70; index++)
            host.Tick(0.015d);

        (byte[] Body, double Time)[] positions = sent
            .Where(static entry =>
                ActionOpcode(entry.Body)
                    == AutonomousPosition.AutonomousPositionAction)
            .ToArray();
        Assert.InRange(positions.Length, 1, 2);
        Assert.True(positions[^1].Time >= 1d);
        if (positions.Length == 2)
        {
            Assert.True(
                positions[1].Time - positions[0].Time >= 0.99d);
        }
        Assert.DoesNotContain(
            sent,
            entry => ActionOpcode(entry.Body)
                == MoveToState.MoveToStateAction);
    }

    [Fact]
    public void TeardownRetriesOnlyTheUnfinishedSuffix()
    {
        var operations = new FixtureSessionOperations();
        var writer = new FailOnceTextWriter();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(writer),
            operations);
        Assert.Equal(
            RuntimeSessionStartStatus.Connected,
            host.Start().Status);
        writer.FailNextWrite = true;

        Assert.Throws<IOException>(host.Dispose);
        Assert.Equal(1, operations.DisposedSessionCount);

        host.Dispose();

        Assert.Equal(1, operations.DisposedSessionCount);
        Assert.True(host.Runtime.CaptureOwnership().IsConverged);
    }

    [Fact]
    public void WorldProjectionHydratesCanonicalMovementAndTeleportState()
    {
        var operations = new FixtureSessionOperations();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        using var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(TextWriter.Null),
            operations);
        GameRuntime runtime = host.Runtime;
        const uint player = 0x50000002u;
        runtime.PlayerIdentity.ServerGuid = player;
        AddFlatLandblock(runtime.EntityObjects.Physics.Engine);
        RuntimeEntityRecord record = runtime.EntityObjects
            .RegisterEntity(Spawn(player))
            .Canonical!;
        Assert.True(runtime.EntityObjects.ApplyAcceptedSpawn(
            record,
            record.CreateIntegrationVersion,
            record.Snapshot,
            replaceGeneration: false));
        var collision = new FixtureCollisionNeighborhood();
        var projection = new HeadlessSessionWorldProjection(
            runtime,
            collision);

        projection.ProjectSpawn(record, isLocalPlayer: true);
        PlayerMovementController controller =
            Assert.IsType<PlayerMovementController>(
                runtime.MovementOwner.Controller);
        controller.SetPosition(
            new Vector3(48f, 49f, 50f),
            0xA9B40001u);
        projection.ProjectPosition(
            record,
            isLocalPlayer: true,
            PositionTimestampDisposition.Apply);

        Assert.Same(controller, runtime.MovementOwner.Controller);
        Assert.Equal(record.LocalEntityId, controller.LocalEntityId);
        Assert.Equal(new Vector3(48f, 49f, 50f), controller.Position);
        Assert.Equal(
            0xA9B40000u,
            controller.CellId & 0xFFFF0000u);
        Assert.True((controller.CellId & 0xFFFFu) < 0x0100u);
        projection.BeginTeleport();
        Assert.Equal(PlayerState.PortalSpace, controller.State);

        RuntimeDestinationReadiness readiness =
            projection.PrepareDestination(
                revealGeneration: 7,
                new RuntimeTeleportDestination(
                    player,
                    InstanceSequence: 1,
                    PositionSequence: 2,
                    TeleportSequence: 1,
                    ForcePositionSequence: 0,
                    new Position(
                        0xA9B40001u,
                        new Vector3(96f, 97f, 50f),
                        Quaternion.Identity)));

        Assert.True(readiness.IsCollisionReady);
        Assert.False(readiness.IsUnhydratable);
        Assert.Equal(PlayerState.InWorld, controller.State);
        Assert.Equal(3, collision.CenterCount);
        Assert.Equal(0xA9B40001u, collision.LastCell);
    }

    [Fact]
    public void WorldProjectionIgnoresNormalEchoButBlipsForcePosition()
    {
        var operations = new FixtureSessionOperations();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        using var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(TextWriter.Null),
            operations);
        GameRuntime runtime = host.Runtime;
        const uint player = 0x50000003u;
        runtime.PlayerIdentity.ServerGuid = player;
        AddFlatLandblock(runtime.EntityObjects.Physics.Engine);
        RuntimeEntityRecord record = runtime.EntityObjects
            .RegisterEntity(Spawn(player))
            .Canonical!;
        Assert.True(runtime.EntityObjects.ApplyAcceptedSpawn(
            record,
            record.CreateIntegrationVersion,
            record.Snapshot,
            replaceGeneration: false));
        var collision = new FixtureCollisionNeighborhood();
        var projection = new HeadlessSessionWorldProjection(
            runtime,
            collision);
        projection.ProjectSpawn(record, isLocalPlayer: true);
        PlayerMovementController controller =
            Assert.IsType<PlayerMovementController>(
                runtime.MovementOwner.Controller);

        controller.SetPosition(
            new Vector3(48f, 49f, 50f),
            0xA9B40001u);
        projection.ProjectPosition(
            record,
            isLocalPlayer: true,
            PositionTimestampDisposition.Apply);

        Assert.Equal(new Vector3(48f, 49f, 50f), controller.Position);

        var force = new WorldSession.EntityPositionUpdate(
            player,
            record.Snapshot.Position!.Value with
            {
                PositionX = 72f,
                PositionY = 73f,
            },
            Velocity: null,
            PlacementId: null,
            IsGrounded: true,
            InstanceSequence: 1,
            PositionSequence: 2,
            TeleportSequence: 0,
            ForcePositionSequence: 1);
        Assert.True(runtime.EntityObjects.TryApplyPosition(
            force,
            isLocalPlayer: true,
            forcePositionRotation: Quaternion.Identity,
            currentLocalVelocity: controller.BodyVelocity,
            projectionRequiresTeleportHook: false,
            acknowledgeProjection: null,
            out PositionTimestampDisposition disposition,
            out _,
            out _));
        Assert.Equal(
            PositionTimestampDisposition.ForcePosition,
            disposition);
        projection.ProjectPosition(
            record,
            isLocalPlayer: true,
            disposition);

        Assert.Equal(new Vector3(72f, 73f, 50f), controller.Position);
        Assert.Equal(2, collision.CenterCount);
    }

    [Fact]
    public void PlacementReceiptValidationDoesNotRegainMovementOrPhysicsAuthority()
    {
        var operations = new FixtureSessionOperations();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        using var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(TextWriter.Null),
            operations);
        GameRuntime runtime = host.Runtime;
        const uint player = 0x50000004u;
        runtime.PlayerIdentity.ServerGuid = player;
        AddFlatLandblock(runtime.EntityObjects.Physics.Engine);
        RuntimeEntityRecord record = runtime.EntityObjects
            .RegisterEntity(Spawn(player))
            .Canonical!;
        Assert.True(runtime.EntityObjects.ApplyAcceptedSpawn(
            record,
            record.CreateIntegrationVersion,
            record.Snapshot,
            replaceGeneration: false));
        var directProjection = new HeadlessSessionWorldProjection(
            runtime,
            new FixtureCollisionNeighborhood());
        directProjection.ProjectSpawn(record, isLocalPlayer: true);
        PlayerMovementController controller = Assert.IsType<
            PlayerMovementController>(runtime.MovementOwner.Controller);
        Vector3 positionBefore = controller.Position;
        Quaternion orientationBefore = controller.BodyOrientation;
        RuntimePhysicsOwnershipSnapshot physicsBefore =
            runtime.EntityObjects.Physics.CaptureOwnership();
        RuntimePlacementProjectionSnapshot receipt = Placement(
            runtime,
            record,
            RuntimePlacementProjectionKind.Place,
            new Vector3(600f, 601f, 602f),
            Quaternion.CreateFromAxisAngle(Vector3.UnitY, 1.2f));

        var receiptSink = new HeadlessRuntimePlacementProjectionSink(runtime);
        Assert.True(receiptSink.TryApply(in receipt));

        Assert.Equal(positionBefore, controller.Position);
        Assert.Equal(orientationBefore, controller.BodyOrientation);
        Assert.Equal(
            physicsBefore,
            runtime.EntityObjects.Physics.CaptureOwnership());
    }

    [Fact]
    public void PlacementReceiptUsesExactIncarnationAndDiscardIsAckOnly()
    {
        var operations = new FixtureSessionOperations();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        using var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(TextWriter.Null),
            operations);
        GameRuntime runtime = host.Runtime;
        RuntimeEntityRecord record = runtime.EntityObjects
            .RegisterEntity(Spawn(0x50000005u))
            .Canonical!;
        Assert.True(runtime.EntityObjects.ApplyAcceptedSpawn(
            record,
            record.CreateIntegrationVersion,
            record.Snapshot,
            replaceGeneration: false));
        var projection = new HeadlessRuntimePlacementProjectionSink(runtime);
        RuntimePlacementProjectionSnapshot place = Placement(
            runtime,
            record,
            RuntimePlacementProjectionKind.Place,
            Vector3.One,
            Quaternion.Identity);
        RuntimePlacementProjectionSnapshot stale = place with
        {
            Token = place.Token with
            {
                Entity = place.Token.Entity with
                {
                    Incarnation = unchecked((ushort)(
                        place.Token.Entity.Incarnation + 1)),
                },
            },
        };
        RuntimePlacementProjectionSnapshot discard = stale with
        {
            Kind = RuntimePlacementProjectionKind.Discard,
            Token = stale.Token with
            {
                SessionLifetimeVersion = ulong.MaxValue,
            },
        };

        Assert.False(projection.TryApply(in stale));
        Assert.True(projection.TryApply(in discard));
    }

    [Fact]
    public void ExecutorCompletedReceiptIsAcknowledgeOnlyRegardlessOfRecordValidity()
    {
        // F1: mirrors PlacementReceiptUsesExactIncarnationAndDiscardIsAckOnly's
        // stale-token half - proves ExecutorCompleted is acknowledged
        // unconditionally (never gated by the record-lookup/portal-shape
        // checks Place/Withdraw depend on), so a genuinely stale/mismatched
        // token can never wedge the FIFO behind it.
        var operations = new FixtureSessionOperations();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        using var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(TextWriter.Null),
            operations);
        GameRuntime runtime = host.Runtime;
        RuntimeEntityRecord record = runtime.EntityObjects
            .RegisterEntity(Spawn(0x50000006u))
            .Canonical!;
        Assert.True(runtime.EntityObjects.ApplyAcceptedSpawn(
            record,
            record.CreateIntegrationVersion,
            record.Snapshot,
            replaceGeneration: false));
        var sink = new HeadlessRuntimePlacementProjectionSink(runtime);
        RuntimePlacementProjectionSnapshot completion = Placement(
            runtime,
            record,
            RuntimePlacementProjectionKind.ExecutorCompleted,
            Vector3.One,
            Quaternion.Identity);
        RuntimePlacementProjectionSnapshot stale = completion with
        {
            Token = completion.Token with
            {
                Entity = completion.Token.Entity with
                {
                    Incarnation = unchecked((ushort)(
                        completion.Token.Entity.Incarnation + 1)),
                },
                SessionLifetimeVersion = ulong.MaxValue,
            },
        };

        Assert.True(sink.TryApply(in completion));
        Assert.True(sink.TryApply(in stale));
    }

    [Fact]
    public void SessionEventRouteOwnsOneObserverAndUnsubscribesBeforeNetworkDetach()
    {
        var operations = new FixtureSessionOperations();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        using var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(TextWriter.Null),
            operations);
        GameRuntime runtime = host.Runtime;
        int subscriberCountDuringDetach = -1;
        var inner = new FixtureEventRoute(
            onDispose: () => subscriberCountDuringDetach =
                runtime.EntityObjects.Events.PlacementSubscriberCount);
        var placements = new HeadlessRuntimePlacementProjectionSink(runtime);
        var route = new HeadlessSessionEventRoute(
            inner,
            runtime,
            placements);

        Assert.Equal(
            0,
            runtime.EntityObjects.Events.PlacementSubscriberCount);
        route.Attach();
        route.Attach();
        Assert.Equal(
            1,
            runtime.EntityObjects.Events.PlacementSubscriberCount);
        Assert.Equal(1, inner.AttachCount);

        route.Dispose();
        route.Dispose();

        Assert.Equal(0, subscriberCountDuringDetach);
        Assert.Equal(
            0,
            runtime.EntityObjects.Events.PlacementSubscriberCount);
        Assert.Equal(1, inner.DisposeCount);
    }

    [Fact]
    public void ReplacementSessionEventRouteGetsOneFreshObserver()
    {
        var operations = new FixtureSessionOperations();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        using var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(TextWriter.Null),
            operations);
        GameRuntime runtime = host.Runtime;
        var placements = new HeadlessRuntimePlacementProjectionSink(runtime);

        var first = new HeadlessSessionEventRoute(
            new FixtureEventRoute(),
            runtime,
            placements);
        first.Attach();
        Assert.Equal(
            1,
            runtime.EntityObjects.Events.PlacementSubscriberCount);
        first.Dispose();
        Assert.Equal(
            0,
            runtime.EntityObjects.Events.PlacementSubscriberCount);

        var replacement = new HeadlessSessionEventRoute(
            new FixtureEventRoute(),
            runtime,
            placements);
        replacement.Attach();
        Assert.Equal(
            1,
            runtime.EntityObjects.Events.PlacementSubscriberCount);
        replacement.Dispose();
        Assert.Equal(
            0,
            runtime.EntityObjects.Events.PlacementSubscriberCount);
    }

    [Fact]
    public void SessionEventRouteRetryDoesNotRestorePlacementObserver()
    {
        var operations = new FixtureSessionOperations();
        using var credential = new HeadlessCredentialSecret(
            "fixture",
            "password");
        using var host = new HeadlessSessionHost(
            Descriptor(),
            credential,
            new HeadlessDiagnosticWriter(TextWriter.Null),
            operations);
        GameRuntime runtime = host.Runtime;
        var inner = new FixtureEventRoute
        {
            DisposeFailuresRemaining = 1,
        };
        var route = new HeadlessSessionEventRoute(
            inner,
            runtime,
            new HeadlessRuntimePlacementProjectionSink(runtime));
        route.Attach();

        Assert.Throws<IOException>(route.Dispose);
        Assert.Equal(
            0,
            runtime.EntityObjects.Events.PlacementSubscriberCount);
        Assert.Equal(1, inner.DisposeCount);

        route.Dispose();

        Assert.Equal(2, inner.DisposeCount);
        Assert.Equal(
            0,
            runtime.EntityObjects.Events.PlacementSubscriberCount);
    }

    [Fact]
    public void CollisionTransactionCancelsPostAdmissionFaultWithoutWithdrawingActiveWorld()
    {
        using var lifetime = new RuntimeEntityObjectLifetime();
        RuntimePhysicsState physics = lifetime.Physics;
        const uint landblockId = 0xA9B4FFFFu;
        CompleteCollisionGeneration(
            physics,
            landblockId,
            afterAdmission: null,
            (admission, prepared) =>
                physics.StageCollisionAssets(
                    admission,
                    prepared,
                    CollisionAssets(landblockId, 10f)));

        Assert.Throws<FixtureCollisionPublicationException>(() =>
            CompleteCollisionGeneration(
                physics,
                landblockId,
                _ => throw new FixtureCollisionPublicationException(),
                (_, _) => throw new InvalidOperationException(
                    "Staging must not run after the injected admission fault.")));

        Assert.Equal(10f, physics.Engine.SampleTerrainZ(1f, 1f));
        RuntimePhysicsOwnershipSnapshot ownership = physics.CaptureOwnership();
        Assert.Equal(1, ownership.LandblockCount);
        Assert.Equal(0, ownership.CollisionAdmissionCount);
    }

    [Fact]
    public void CollisionTransactionYieldsTheFirstNonterminalRuntimePoll()
    {
        using var lifetime = new RuntimeEntityObjectLifetime();
        RuntimePhysicsState physics = lifetime.Physics;
        const uint landblockId = 0xA9B4FFFFu;
        HeadlessCollisionGenerationTransaction transaction =
            HeadlessCollisionGenerationTransaction.Begin(
                physics,
                landblockId,
                afterAdmission: null,
                (admission, prepared) =>
                    physics.StageCollisionAssets(
                        admission,
                        prepared,
                        CollisionAssets(landblockId, 10f)));

        HeadlessCollisionGenerationAdvance advance;
        do
        {
            advance = transaction.Advance();
            Assert.True(advance.Progressed);
        }
        while (!advance.YieldToCaller);

        Assert.False(advance.Completed);
        Assert.False(advance.WaitingForProjectionAcknowledgement);
        Assert.False(transaction.CompletionCommitted);

        do
        {
            advance = transaction.Advance();
            Assert.True(advance.Progressed);
        }
        while (!advance.Completed && !advance.YieldToCaller);
        if (!advance.Completed)
            advance = transaction.Advance();

        Assert.True(advance.Completed);
        Assert.True(transaction.EngineMutationCommitted);
        Assert.True(transaction.CompletionCommitted);
        Assert.Equal(0, physics.CaptureOwnership().CollisionAdmissionCount);
    }

    [Fact]
    public void CollisionTransactionRetainsPostEngineCancellationUntilPlaceAck()
    {
        using var lifetime = new RuntimeEntityObjectLifetime();
        RuntimePhysicsState physics = lifetime.Physics;
        const uint landblockId = 0xA9B4FFFFu;
        CompleteCollisionGeneration(
            physics,
            landblockId,
            afterAdmission: null,
            (admission, prepared) =>
                physics.StageCollisionAssets(
                    admission,
                    prepared,
                    CollisionAssets(landblockId, 10f)));

        const uint guid = 0x70004201u;
        const uint cell = 0xA9B40001u;
        Vector3 position = new(10f, 10f, 0f);
        RuntimeEntityRecord record = lifetime.RegisterEntity(
            Spawn(guid)).Canonical!;
        lifetime.Entities.SetFinalPhysicsState(record, PhysicsStateFlags.Gravity);
        lifetime.Entities.SetFullCell(record, cell, landblockId);
        var body = new PhysicsBody
        {
            Position = position,
            Orientation = Quaternion.Identity,
            LastUpdateTime = 1d,
            State = PhysicsStateFlags.Gravity,
            TransientState = TransientStateFlags.Active,
        };
        body.SnapToCell(cell, position, position);
        lifetime.Entities.SetPhysicsBody(record, body);
        record.ObjectClock.Activate();
        physics.AcknowledgeSpatialProjection(record, spatial: true);
        RuntimePlacementProjectionToken seeded = SeedRuntimePlacement(
            physics,
            record,
            cell,
            position);
        Assert.True(physics.SetPosition.AcknowledgeProjection(seeded));

        HeadlessCollisionGenerationTransaction transaction =
            HeadlessCollisionGenerationTransaction.Begin(
                physics,
                landblockId,
                afterAdmission: null,
                (admission, prepared) =>
                    physics.StageCollisionAssets(
                        admission,
                        prepared,
                        CollisionAssets(landblockId, 20f)));
        HeadlessCollisionGenerationAdvance advance;
        do
        {
            advance = transaction.Advance();
        }
        while (!advance.WaitingForProjectionAcknowledgement);
        Assert.False(transaction.EngineMutationCommitted);
        Assert.True(physics.SetPosition.TryPeekProjection(
            out RuntimePlacementProjectionSnapshot withdrawal));
        Assert.True(physics.SetPosition.AcknowledgeProjection(withdrawal.Token));

        do
        {
            advance = transaction.Advance();
        }
        while (!advance.WaitingForProjectionAcknowledgement);
        Assert.True(transaction.EngineMutationCommitted);
        Assert.True(physics.SetPosition.TryPeekProjection(
            out RuntimePlacementProjectionSnapshot placement));

        Assert.False(transaction.TryCancel());
        Assert.True(physics.SetPosition.AcknowledgeProjection(placement.Token));
        Assert.True(transaction.TryCancel());
        RuntimePhysicsOwnershipSnapshot ownership = physics.CaptureOwnership();
        Assert.Equal(0, ownership.CollisionPrefixMutationCount);
        Assert.Equal(0, ownership.CollisionAdmissionCount);
    }

    [Fact]
    public void CollisionTransactionCancelsStagingFaultWithoutWithdrawingActiveWorld()
    {
        using var lifetime = new RuntimeEntityObjectLifetime();
        RuntimePhysicsState physics = lifetime.Physics;
        const uint landblockId = 0xA9B4FFFFu;
        CompleteCollisionGeneration(
            physics,
            landblockId,
            afterAdmission: null,
            (admission, prepared) =>
                physics.StageCollisionAssets(
                    admission,
                    prepared,
                    CollisionAssets(landblockId, 10f)));

        Assert.Throws<FixtureCollisionPublicationException>(() =>
            CompleteCollisionGeneration(
                physics,
                landblockId,
                afterAdmission: null,
                (admission, prepared) =>
                {
                    physics.StageCollisionAssets(
                        admission,
                        prepared,
                        CollisionAssets(landblockId, 25f));
                    throw new FixtureCollisionPublicationException();
                }));

        Assert.Equal(10f, physics.Engine.SampleTerrainZ(1f, 1f));
        RuntimePhysicsOwnershipSnapshot ownership = physics.CaptureOwnership();
        Assert.Equal(1, ownership.LandblockCount);
        Assert.Equal(0, ownership.CollisionAdmissionCount);
    }

    private static HeadlessSessionDescriptor Descriptor(
        HeadlessCredentialProviderKind provider =
            HeadlessCredentialProviderKind.Environment,
        string credentialReference = "BOT_PASSWORD") => new()
    {
        Id = "bot",
        Endpoint = new HeadlessEndpointDescriptor
        {
            Host = "127.0.0.1",
            Port = 9000,
        },
        Account = "account",
        Character = new HeadlessCharacterSelector
        {
            Name = "headless",
        },
        Policy = new HeadlessBotPolicyDescriptor
        {
            Id = "idle",
        },
        Credential = new HeadlessCredentialReference
        {
            Provider = provider,
            Reference = credentialReference,
        },
    };

    private static void HydrateGroundedPlayer(GameRuntime runtime)
    {
        const uint player = 0x50000002u;
        PhysicsEngine engine = runtime.EntityObjects.Physics.Engine;
        AddFlatLandblock(engine);

        RuntimeEntityRecord record = runtime.EntityObjects
            .RegisterEntity(Spawn(player))
            .Canonical!;
        Assert.True(runtime.EntityObjects.ApplyAcceptedSpawn(
            record,
            record.CreateIntegrationVersion,
            record.Snapshot,
            replaceGeneration: false));
        var controller = new PlayerMovementController(engine);
        controller.SetPosition(
            new Vector3(96f, 97f, 50f),
            0xA9B40001u,
            new Vector3(96f, 97f, 50f));
        runtime.MovementOwner.Controller = controller;
    }

    private static void CompleteCollisionGeneration(
        RuntimePhysicsState physics,
        uint landblockId,
        Action<RuntimeCollisionAdmission>? afterAdmission,
        Action<RuntimeCollisionAdmission,
            PreparedLandblockCollisionGeneration> stage)
    {
        HeadlessCollisionGenerationTransaction transaction =
            HeadlessCollisionGenerationTransaction.Begin(
                physics,
                landblockId,
                afterAdmission,
                stage);
        while (true)
        {
            HeadlessCollisionGenerationAdvance advance = transaction.Advance();
            if (advance.Completed)
                return;
            Assert.True(advance.Progressed);
            Assert.False(advance.WaitingForProjectionAcknowledgement);
        }
    }

    private static RuntimePlacementProjectionToken SeedRuntimePlacement(
        RuntimePhysicsState physics,
        RuntimeEntityRecord record,
        uint cell,
        Vector3 position)
    {
        Type coreMarker = typeof(PhysicsEngine);
        Type requestType = coreMarker.Assembly.GetType(
            "AcDream.Core.Physics.PhysicsSetPositionRequest",
            throwOnError: true)!;
        Type flagsType = coreMarker.Assembly.GetType(
            "AcDream.Core.Physics.PhysicsSetPositionFlags",
            throwOnError: true)!;
        Type placementClassType = coreMarker.Assembly.GetType(
            "AcDream.Core.Physics.PhysicsPlacementClass",
            throwOnError: true)!;
        object request = Activator.CreateInstance(
            requestType,
            BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic,
            binder: null,
            args:
            [
                position,
                Quaternion.Identity,
                cell,
                position,
                ImmutableArray<FlatCollisionSphere>.Empty,
                1f,
                0.4f,
                0.4f,
                PhysicsStateFlags.None,
                ObjectInfoState.None,
                0u,
                Enum.ToObject(placementClassType, 0),
                Enum.ToObject(flagsType, 0x011u),
                Vector3.Zero,
                0f,
                0f,
                0u,
                cell,
            ],
            culture: null)!;
        Type runtimeMarker = typeof(RuntimePhysicsState);
        Type commandType = runtimeMarker.Assembly.GetType(
            "AcDream.Runtime.Physics.RuntimeSetPositionCommand",
            throwOnError: true)!;
        Type kindType = runtimeMarker.Assembly.GetType(
            "AcDream.Runtime.Physics.RuntimeSetPositionOperationKind",
            throwOnError: true)!;
        object command = Activator.CreateInstance(
            commandType,
            BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic,
            binder: null,
            args:
            [
                request,
                Enum.ToObject(kindType, 2),
                10d,
                0UL,
                0f,
                0f,
                default(RuntimePortalPlacementAuthority),
            ],
            culture: null)!;
        MethodInfo apply = physics.SetPosition.GetType().GetMethod(
            "Apply",
            BindingFlags.Instance | BindingFlags.NonPublic)
            ?? throw new MissingMethodException("Runtime SetPosition.Apply");
        object outcome = apply.Invoke(
            physics.SetPosition,
            [record, record.PositionAuthorityVersion, command])!;
        return (RuntimePlacementProjectionToken)(outcome.GetType().GetProperty(
            "Projection",
            BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic)
            ?.GetValue(outcome)
            ?? throw new MissingMemberException("Runtime placement projection"));
    }

    private static RuntimeLandblockCollisionAssets CollisionAssets(
        uint landblockId,
        float terrainHeight)
    {
        var heights = new byte[81];
        var table = new float[256];
        table[0] = terrainHeight;
        return new RuntimeLandblockCollisionAssets(
            landblockId,
            new TerrainSurface(heights, table),
            Array.Empty<CellSurface>(),
            Array.Empty<PortalPlane>(),
            0f,
            0f,
            0u);
    }

    private sealed class FixtureCollisionPublicationException : Exception;

    private static void AddFlatLandblock(PhysicsEngine engine)
    {
        var heights = new byte[81];
        Array.Fill(heights, (byte)50);
        var heightTable = new float[256];
        for (int index = 0; index < heightTable.Length; index++)
            heightTable[index] = index;
        engine.AddLandblock(
            0xA9B4FFFFu,
            new TerrainSurface(heights, heightTable),
            [],
            [],
            worldOffsetX: 0f,
            worldOffsetY: 0f);
    }

    private static WorldSession.EntitySpawn Spawn(uint guid)
    {
        var position = new CreateObject.ServerPosition(
            0xA9B40001u,
            96f,
            97f,
            50f,
            1f,
            0f,
            0f,
            0f);
        var timestamps = new PhysicsTimestamps(
            Position: 1,
            Movement: 1,
            State: 1,
            Vector: 1,
            Teleport: 0,
            ServerControlledMove: 1,
            ForcePosition: 0,
            ObjDesc: 1,
            Instance: 1);
        var physics = new PhysicsSpawnData(
            RawState: (uint)PhysicsStateFlags.ReportCollisions,
            Position: position,
            Movement: null,
            AnimationFrame: null,
            SetupTableId: 0x02000001u,
            MotionTableId: null,
            SoundTableId: null,
            PhysicsScriptTableId: null,
            Parent: null,
            Children: null,
            Scale: null,
            Friction: null,
            Elasticity: null,
            Translucency: null,
            Velocity: null,
            Acceleration: null,
            AngularVelocity: null,
            DefaultScriptType: null,
            DefaultScriptIntensity: null,
            Timestamps: timestamps);
        return new WorldSession.EntitySpawn(
            guid,
            position,
            0x02000001u,
            [],
            [],
            [],
            null,
            null,
            "Headless",
            null,
            null,
            null,
            PhysicsState: physics.RawState,
            InstanceSequence: 1,
            MovementSequence: 1,
            ServerControlSequence: 1,
            PositionSequence: 1,
            Physics: physics);
    }

    private static RuntimePlacementProjectionSnapshot Placement(
        GameRuntime runtime,
        RuntimeEntityRecord record,
        RuntimePlacementProjectionKind kind,
        Vector3 position,
        Quaternion orientation)
    {
        RuntimeEntityKey key = Assert.IsType<RuntimeEntityKey>(record.Key);
        var token = new RuntimePlacementProjectionToken(
            Sequence: 1,
            Revision: 1,
            Entity: key,
            PositionAuthorityVersion: record.PositionAuthorityVersion,
            SpatialAuthorityVersion: record.SpatialAuthorityVersion,
            PlacementCommitVersion: record.PlacementCommitVersion,
            SessionLifetimeVersion:
                runtime.EntityObjects.Entities.SessionLifetimeVersion,
            ExactCellId: record.FullCellId,
            CollisionGeneration: 1,
            Portal: default);
        return new RuntimePlacementProjectionSnapshot(
            token,
            kind,
            position,
            orientation,
            CellLocalPosition: position,
            InContact: false,
            OnWalkable: false);
    }

    private static uint ActionOpcode(byte[] body) =>
        BinaryPrimitives.ReadUInt32LittleEndian(
            body.AsSpan(8, sizeof(uint)));

    private sealed class FixtureSessionOperations : ILiveSessionOperations
    {
        public List<WorldSession> Sessions { get; } = [];
        public int CreatedSessionCount { get; private set; }
        public int DisposedSessionCount { get; private set; }
        public string? LastUser { get; private set; }
        public string? LastPassword { get; private set; }

        public IPEndPoint ResolveEndpoint(string host, int port) =>
            new(IPAddress.Loopback, port);

        public WorldSession CreateSession(IPEndPoint endpoint)
        {
            CreatedSessionCount++;
            var session = new WorldSession(endpoint);
            Sessions.Add(session);
            return session;
        }

        public void Connect(
            WorldSession session,
            string user,
            string password)
        {
            LastUser = user;
            LastPassword = password;
        }

        public CharacterList.Parsed GetCharacters(
            WorldSession session) =>
            new(
                0u,
                [
                    new CharacterList.Character(
                        0x50000001u,
                        "Other",
                        0u),
                    new CharacterList.Character(
                        0x50000002u,
                        "Headless",
                        0u),
                ],
                [],
                11,
                "account",
                true,
                true);

        public void EnterWorld(
            WorldSession session,
            int activeCharacterIndex)
        {
        }

        public void Tick(WorldSession session)
        {
        }

        public void DisposeSession(WorldSession session)
        {
            DisposedSessionCount++;
            session.Dispose();
        }
    }

    private sealed class FailOnceTextWriter : StringWriter
    {
        public bool FailNextWrite { get; set; }

        public override void WriteLine(string? value)
        {
            if (FailNextWrite)
            {
                FailNextWrite = false;
                throw new IOException("fixture write failure");
            }
            base.WriteLine(value);
        }
    }

    private sealed class FixtureCollisionNeighborhood
        : IHeadlessCollisionNeighborhood
    {
        public int CenterCount { get; private set; }
        public uint LastCell { get; private set; }

        public void CenterOn(uint fullCellId)
        {
            CenterCount++;
            LastCell = fullCellId;
        }

        public bool IsReady(uint fullCellId) =>
            fullCellId == LastCell;
    }

    private sealed class FixtureEventRoute(
        Action? onDispose = null) : ILiveSessionEventRouting
    {
        public int AttachCount { get; private set; }
        public int DisposeCount { get; private set; }
        public int DisposeFailuresRemaining { get; set; }

        public void Attach() => AttachCount++;

        public void Dispose()
        {
            DisposeCount++;
            onDispose?.Invoke();
            if (DisposeFailuresRemaining > 0)
            {
                DisposeFailuresRemaining--;
                throw new IOException("fixture route detach failure");
            }
        }
    }

}