using System.Collections.ObjectModel;
using System.Diagnostics.CodeAnalysis;
using System.Numerics;
using AcDream.App.Rendering;
using AcDream.App.Rendering.Gpu;
using AcDream.App.Rendering.Gpu.Vk;
using AcDream.App.Rendering.Wb;
using AcDream.App.Rendering.Walk;
using AcDream.App.Tests.Rendering.Gpu;
using AcDream.Content;
using AcDream.Core.Meshing;
using DatReaderWriter;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Enums;
using DatReaderWriter.Lib.IO;
using Microsoft.Extensions.Logging.Abstractions;

namespace AcDream.App.Tests.Rendering.Walk;

/// <summary>
/// Campaign FW stage FW2: <see cref="WbDrawDispatcher.BuildOrderedMergeRuns"/>
/// (pure CPU merge-run legality) and, from Campaign FW stage FW3.4a,
/// <see cref="WbDrawDispatcher.PrepareOrderedStream"/> +
/// <see cref="WbDrawDispatcher.DrawOrderedRange"/> (the same legality proven
/// through actual recorded RHI calls against <see cref="RecordingGpuDevice"/>,
/// replacing the single <c>SubmitOrderedStream</c> call those two now split).
/// </summary>
public sealed class OrderPreservingSubmitterTests
{
    private static OrderedDrawCommand MakeCommand(
        int index,
        WalkDrawStage stage = WalkDrawStage.Terrain,
        TranslucencyKind translucency = TranslucencyKind.Opaque,
        CullMode cullMode = CullMode.CounterClockwise,
        uint detailCategory = 0) =>
        new(
            Key: new GroupKey(
                FirstIndex: (uint)index * 3,
                BaseVertex: index * 4,
                IndexCount: 3,
                TextureSlot: new GpuTextureSlot((uint)index),
                TextureLayer: 0,
                Translucency: translucency,
                FoliageFlags: 0,
                CullMode: cullMode),
            Transform: Matrix4x4.CreateTranslation(index, index * 2, index * 3),
            Stage: stage,
            CellId: 0x8C040100u + (uint)index,
            ClipSlot: 0,
            Lights: WbDrawDispatcher.InstanceLightSet.Disabled,
            IndoorFlag: 0,
            Alpha: 1f,
            SelectionLighting: Vector2.Zero,
            DetailCategory: detailCategory);

    private static OrderedDrawStream StreamOf(params OrderedDrawCommand[] commands)
    {
        var stream = new OrderedDrawStream();
        foreach (OrderedDrawCommand command in commands)
            stream.Append(command);
        return stream;
    }

    // ── Pure BuildOrderedMergeRuns — no GPU device ─────────────────────────

    [Fact]
    public void BuildOrderedMergeRuns_MergesThreeAdjacentSameStateCommandsIntoOneRun()
    {
        OrderedDrawStream stream = StreamOf(
            MakeCommand(0), MakeCommand(1), MakeCommand(2));

        List<WbDrawDispatcher.OrderedMergeRun> runs =
            WbDrawDispatcher.BuildOrderedMergeRuns(stream);

        WbDrawDispatcher.OrderedMergeRun run = Assert.Single(runs);
        Assert.Equal(0, run.FirstCommand);
        Assert.Equal(3, run.CommandCount);
    }

    [Fact]
    public void BuildOrderedMergeRuns_SplitsOnAPipelineBucketChange()
    {
        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, translucency: TranslucencyKind.Opaque),
            MakeCommand(1, translucency: TranslucencyKind.Opaque),
            MakeCommand(2, translucency: TranslucencyKind.AlphaBlend));

        List<WbDrawDispatcher.OrderedMergeRun> runs =
            WbDrawDispatcher.BuildOrderedMergeRuns(stream);

        Assert.Equal(
            [
                new WbDrawDispatcher.OrderedMergeRun(0, 2),
                new WbDrawDispatcher.OrderedMergeRun(2, 1),
            ],
            runs);
    }

    [Fact]
    public void BuildOrderedMergeRuns_SplitsOnACullModeChange()
    {
        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, cullMode: CullMode.None),
            MakeCommand(1, cullMode: CullMode.None),
            MakeCommand(2, cullMode: CullMode.Clockwise));

        List<WbDrawDispatcher.OrderedMergeRun> runs =
            WbDrawDispatcher.BuildOrderedMergeRuns(stream);

        Assert.Equal(
            [
                new WbDrawDispatcher.OrderedMergeRun(0, 2),
                new WbDrawDispatcher.OrderedMergeRun(2, 1),
            ],
            runs);
    }

    /// <summary>
    /// The load-bearing new assertion: two commands whose material state
    /// (bucket, cull mode, detail category) is IDENTICAL still split into two
    /// runs when their <see cref="WalkDrawStage"/> differs. Nothing about the
    /// deferred-alpha template this submitter borrows from ever had to
    /// consider stage — walk order introduces it.
    /// </summary>
    [Fact]
    public void BuildOrderedMergeRuns_SplitsOnAStageChangeEvenWithIdenticalMaterialState()
    {
        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, stage: WalkDrawStage.Terrain),
            MakeCommand(1, stage: WalkDrawStage.CellStatic));

        List<WbDrawDispatcher.OrderedMergeRun> runs =
            WbDrawDispatcher.BuildOrderedMergeRuns(stream);

        Assert.Equal(
            [
                new WbDrawDispatcher.OrderedMergeRun(0, 1),
                new WbDrawDispatcher.OrderedMergeRun(1, 1),
            ],
            runs);
    }

    [Fact]
    public void BuildOrderedMergeRuns_ADetailCategoryCommandIsAlwaysSolo()
    {
        OrderedDrawStream stream = StreamOf(
            MakeCommand(0),
            MakeCommand(1, detailCategory: 1),
            MakeCommand(2));

        List<WbDrawDispatcher.OrderedMergeRun> runs =
            WbDrawDispatcher.BuildOrderedMergeRuns(stream);

        Assert.Equal(
            [
                new WbDrawDispatcher.OrderedMergeRun(0, 1),
                new WbDrawDispatcher.OrderedMergeRun(1, 1),
                new WbDrawDispatcher.OrderedMergeRun(2, 1),
            ],
            runs);
    }

    [Fact]
    public void BuildOrderedMergeRuns_ThrowsNotSupportedForAPortalPunchCommand()
    {
        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, stage: WalkDrawStage.Terrain),
            MakeCommand(1, stage: WalkDrawStage.PortalPunch));

        Assert.Throws<NotSupportedException>(
            () => WbDrawDispatcher.BuildOrderedMergeRuns(stream));
    }

    [Fact]
    public void BuildOrderedMergeRuns_EveryCommandBelongsToExactlyOneRunInOrderWithNoGaps()
    {
        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, stage: WalkDrawStage.Terrain, translucency: TranslucencyKind.Opaque, cullMode: CullMode.None),
            MakeCommand(1, stage: WalkDrawStage.Terrain, translucency: TranslucencyKind.Opaque, cullMode: CullMode.None),
            MakeCommand(2, stage: WalkDrawStage.Terrain, translucency: TranslucencyKind.AlphaBlend, cullMode: CullMode.None),
            MakeCommand(3, stage: WalkDrawStage.Terrain, translucency: TranslucencyKind.AlphaBlend, cullMode: CullMode.Clockwise),
            MakeCommand(4, stage: WalkDrawStage.CellStatic, translucency: TranslucencyKind.AlphaBlend, cullMode: CullMode.Clockwise),
            MakeCommand(5, stage: WalkDrawStage.CellStatic, translucency: TranslucencyKind.AlphaBlend, cullMode: CullMode.Clockwise, detailCategory: 1),
            MakeCommand(6, stage: WalkDrawStage.CellStatic, translucency: TranslucencyKind.AlphaBlend, cullMode: CullMode.Clockwise));

        List<WbDrawDispatcher.OrderedMergeRun> runs =
            WbDrawDispatcher.BuildOrderedMergeRuns(stream);

        int coveredThrough = 0;
        int totalCommands = 0;
        foreach (WbDrawDispatcher.OrderedMergeRun run in runs)
        {
            Assert.Equal(coveredThrough, run.FirstCommand);
            Assert.True(run.CommandCount > 0);
            coveredThrough = run.FirstCommand + run.CommandCount;
            totalCommands += run.CommandCount;
        }
        Assert.Equal(stream.Count, coveredThrough);
        Assert.Equal(stream.Count, totalCommands);
    }

    // ── PrepareOrderedStream + DrawOrderedRange — recorded RHI calls against
    // RecordingGpuDevice. Campaign FW3.4a replaced the single
    // SubmitOrderedStream call with this pair (prepare the whole stream once,
    // draw it via one or more ranges) — every test below that used to call
    // SubmitOrderedStream now calls Prepare once and Draw the WHOLE stream as
    // ONE range, which is exactly SubmitOrderedStream's old behavior; the
    // "several ranges" and "bind once" shapes get their own tests further
    // down since they have no FW2 analogue. ────────────────────────────────

    private static void PrepareAndDrawWhole(WbDrawDispatcher dispatcher, DrawScope draw, OrderedDrawStream stream)
    {
        dispatcher.PrepareOrderedStream(draw.Frame, stream, Matrix4x4.Identity);
        if (stream.Count > 0)
            dispatcher.DrawOrderedRange(draw.Pass, 0, stream.Count);
    }

    [Fact]
    public void PrepareThenDraw_AlternatingStateCommandsRecordOneDrawEachInOrder()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, translucency: TranslucencyKind.Opaque),
            MakeCommand(1, translucency: TranslucencyKind.AlphaBlend),
            MakeCommand(2, translucency: TranslucencyKind.Opaque),
            MakeCommand(3, translucency: TranslucencyKind.AlphaBlend));

        PrepareAndDrawWhole(fx.Dispatcher, draw, stream);

        List<(int Start, int Count)> ranges = DecodeDrawRanges(fx.Device);
        Assert.Equal([(0, 1), (1, 1), (2, 1), (3, 1)], ranges);
    }

    [Fact]
    public void PrepareThenDraw_MergesAdjacentSameStateCommandsIntoOneMultiDrawIndirect()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        OrderedDrawStream stream = StreamOf(
            MakeCommand(0), MakeCommand(1), MakeCommand(2));

        PrepareAndDrawWhole(fx.Dispatcher, draw, stream);

        List<(int Start, int Count)> ranges = DecodeDrawRanges(fx.Device);
        Assert.Equal([(0, 3)], ranges);
    }

    [Fact]
    public void PrepareThenDraw_CullModeChangeRecordsSeparateCullCallsAndSplitsTheDraw()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, cullMode: CullMode.None),
            MakeCommand(1, cullMode: CullMode.None),
            MakeCommand(2, cullMode: CullMode.Clockwise));

        PrepareAndDrawWhole(fx.Dispatcher, draw, stream);

        Assert.Equal([(0, 2), (2, 1)], DecodeDrawRanges(fx.Device));

        List<GpuCullMode> cullCalls =
            [.. fx.Device.Calls.OfType<GpuRecordedCullMode>().Select(c => c.CullMode)];
        // ApplyCullModeRhi: CullMode.None -> GpuCullMode.None, CullMode.Clockwise -> GpuCullMode.Front.
        Assert.Equal([GpuCullMode.None, GpuCullMode.Front], cullCalls);
    }

    [Fact]
    public void PrepareThenDraw_StageChangeSplitsTheDrawEvenWithIdenticalMaterialState()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, stage: WalkDrawStage.Terrain),
            MakeCommand(1, stage: WalkDrawStage.CellStatic));

        PrepareAndDrawWhole(fx.Dispatcher, draw, stream);

        Assert.Equal([(0, 1), (1, 1)], DecodeDrawRanges(fx.Device));
    }

    [Fact]
    public void PrepareThenDraw_ADetailCategoryCommandRecordsItsOwnSoloDraw()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        OrderedDrawStream stream = StreamOf(
            MakeCommand(0),
            MakeCommand(1, detailCategory: 1),
            MakeCommand(2));

        PrepareAndDrawWhole(fx.Dispatcher, draw, stream);

        Assert.Equal([(0, 1), (1, 1), (2, 1)], DecodeDrawRanges(fx.Device));
    }

    [Fact]
    public void PrepareThenDraw_OpaqueRunUsesRenderPassZeroAndAlphaBlendRunUsesRenderPassOne()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, translucency: TranslucencyKind.Opaque),
            MakeCommand(1, translucency: TranslucencyKind.AlphaBlend));

        PrepareAndDrawWhole(fx.Dispatcher, draw, stream);

        List<(GpuPushConstants Constants, int Start, int Count)> runs = DecodeRuns(fx.Device);
        Assert.Equal(2, runs.Count);
        Assert.Equal(0, runs[0].Constants.RenderPass);
        Assert.Equal(1, runs[1].Constants.RenderPass);
    }

    [Fact]
    public void PrepareOrderedStream_ThrowsNotSupportedForAPortalPunchCommandBeforeAnyDraw()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, stage: WalkDrawStage.PortalPunch));

        Assert.Throws<NotSupportedException>(
            () => fx.Dispatcher.PrepareOrderedStream(draw.Frame, stream, Matrix4x4.Identity));

        Assert.Empty(fx.Device.Calls.OfType<GpuRecordedMultiDrawIndirect>());
        Assert.Empty(fx.Device.Calls.OfType<GpuRecordedStorageBind>());
    }

    [Fact]
    public void PrepareOrderedStream_EmptyStreamRecordsNoDraws()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        fx.Dispatcher.PrepareOrderedStream(draw.Frame, new OrderedDrawStream(), Matrix4x4.Identity);

        Assert.Empty(fx.Device.Calls.OfType<GpuRecordedMultiDrawIndirect>());
    }

    // ── Campaign FW3.4a — the shapes with no FW2 analogue: drawing the SAME
    // prepared stream as several ranges, the bind-once optimization, the
    // fail-loud range check, and the assert-don't-slice straddle guard. ───

    /// <summary>
    /// The whole point of the split: drawing the SAME stream as TWO ranges
    /// (with the boundary between them supplied to Prepare, exactly as
    /// WalkFrameDriver.Replay supplies its recorded mark positions) produces
    /// the identical total recorded draw/cull/push-constant calls as drawing
    /// it as one range — the range split changes nothing about what reaches
    /// the GPU, only how many DrawOrderedRange calls got there.
    /// </summary>
    [Fact]
    public void DrawOrderedRange_AsTwoRangesAtASegmentBoundary_MatchesOneRangeOverTheWholeStream()
    {
        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, translucency: TranslucencyKind.Opaque),
            MakeCommand(1, translucency: TranslucencyKind.Opaque),
            MakeCommand(2, translucency: TranslucencyKind.Opaque),
            MakeCommand(3, translucency: TranslucencyKind.Opaque));

        using var wholeFx = new DispatcherFixture();
        using (DrawScope draw = wholeFx.BeginDraw())
        {
            wholeFx.Dispatcher.PrepareOrderedStream(draw.Frame, stream, Matrix4x4.Identity);
            wholeFx.Dispatcher.DrawOrderedRange(draw.Pass, 0, stream.Count);
        }
        List<(int Start, int Count)> wholeRanges = DecodeDrawRanges(wholeFx.Device);

        using var splitFx = new DispatcherFixture();
        using (DrawScope draw = splitFx.BeginDraw())
        {
            // Command 2 is a segment boundary (mirrors a mark WalkFrameDriver
            // would record there, e.g. a cell shell between two same-state
            // segments) — without it, all four commands would merge into ONE
            // run; the boundary forces two.
            splitFx.Dispatcher.PrepareOrderedStream(
                draw.Frame, stream, Matrix4x4.Identity, forcedBreaksAscending: [2]);
            splitFx.Dispatcher.DrawOrderedRange(draw.Pass, 0, 2);
            splitFx.Dispatcher.DrawOrderedRange(draw.Pass, 2, 2);
        }
        List<(int Start, int Count)> splitRanges = DecodeDrawRanges(splitFx.Device);

        // The split path draws two runs where the whole-range path drew one
        // (the forced boundary is the only difference) — but every command
        // reaches the GPU exactly once, in order, with identical coverage.
        Assert.Equal([(0, 4)], wholeRanges);
        Assert.Equal([(0, 2), (2, 2)], splitRanges);
    }

    /// <summary>
    /// The FW3.4a perf shape itself: the nine per-instance storage binds plus
    /// the warm-up pipeline bind happen on the FIRST DrawOrderedRange call in
    /// a frame only — a second call over the same prepared payload issues no
    /// further StorageBind calls, which is the whole reason this stage exists
    /// (the old SubmitOrderedStream rebound everything on every call).
    /// </summary>
    [Fact]
    public void DrawOrderedRange_EveryCallRebindsTheStorageSections()
    {
        // The corrected FW3.4a contract (the dense-Arwic device-lost fix):
        // between ordered ranges the walk's leaf draws and RetailAlphaQueue
        // flushes rebind the SAME set-0 slots to THEIR sections, so every
        // DrawOrderedRange call must re-bind its own — a latched skip draws
        // the next range against foreign buffers. Only the ring WRITES are
        // once-per-frame (PrepareOrderedStream); binds repeat per range,
        // exactly like DrawPreparedAlphaBatchRhi.
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        OrderedDrawStream stream = StreamOf(
            MakeCommand(0, stage: WalkDrawStage.Terrain),
            MakeCommand(1, stage: WalkDrawStage.CellStatic));

        fx.Dispatcher.PrepareOrderedStream(draw.Frame, stream, Matrix4x4.Identity);
        fx.Dispatcher.DrawOrderedRange(draw.Pass, 0, 1);
        int boundAfterFirst = fx.Device.Calls.OfType<GpuRecordedStorageBind>().Count();
        Assert.True(boundAfterFirst > 0);

        fx.Dispatcher.DrawOrderedRange(draw.Pass, 1, 1);
        int boundAfterSecond = fx.Device.Calls.OfType<GpuRecordedStorageBind>().Count();

        Assert.Equal(boundAfterFirst * 2, boundAfterSecond);
        // Both commands drew; the rebinds changed nothing about coverage.
        Assert.Equal([(0, 1), (1, 1)], DecodeDrawRanges(fx.Device));
    }

    /// <summary>
    /// Fail-loud range check (mirrors DrawPreparedAlphaBatchRhi's): a range
    /// outside what PrepareOrderedStream uploaded throws rather than drawing
    /// garbage or silently clamping — including a draw attempted before ANY
    /// Prepare call this frame.
    /// </summary>
    [Fact]
    public void DrawOrderedRange_RangeExceedingThePreparedPayload_Throws()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        OrderedDrawStream stream = StreamOf(MakeCommand(0));
        fx.Dispatcher.PrepareOrderedStream(draw.Frame, stream, Matrix4x4.Identity);

        Assert.Throws<ArgumentOutOfRangeException>(
            () => fx.Dispatcher.DrawOrderedRange(draw.Pass, 0, 2));
        Assert.Throws<ArgumentOutOfRangeException>(
            () => fx.Dispatcher.DrawOrderedRange(draw.Pass, 1, 1));
    }

    [Fact]
    public void DrawOrderedRange_BeforeAnyPrepareCallThisFrame_Throws()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        Assert.Throws<ArgumentOutOfRangeException>(
            () => fx.Dispatcher.DrawOrderedRange(draw.Pass, 0, 1));
    }

    /// <summary>
    /// The plan's "assert it" rule: a range that does not align with a merge
    /// run boundary throws rather than silently slicing the run — proven
    /// directly here (skipping the boundary a real WalkFrameDriver mark would
    /// supply) since production code always supplies the boundary and would
    /// never exercise this path.
    /// </summary>
    [Fact]
    public void DrawOrderedRange_RangeStraddlingAMergeRun_Throws()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        // All four commands share stage/bucket/cull — ONE merge run [0, 4) —
        // and no forced break is supplied, so a [0, 2) range straddles it.
        OrderedDrawStream stream = StreamOf(
            MakeCommand(0), MakeCommand(1), MakeCommand(2), MakeCommand(3));
        fx.Dispatcher.PrepareOrderedStream(draw.Frame, stream, Matrix4x4.Identity);

        Assert.Throws<InvalidOperationException>(
            () => fx.Dispatcher.DrawOrderedRange(draw.Pass, 0, 2));
    }

    /// <summary>
    /// Fail-loud invariant: whatever the state pattern, the recorded
    /// MultiDrawIndirect calls' DrawCounts always sum to the stream's Count —
    /// no command is ever silently skipped, and none is drawn twice.
    /// </summary>
    [Fact]
    public void PrepareThenDraw_TotalRecordedDrawCountAlwaysEqualsTheStreamCount()
    {
        using var fx = new DispatcherFixture();
        using DrawScope draw = fx.BeginDraw();

        var stream = new OrderedDrawStream();
        var stages = new[] { WalkDrawStage.Terrain, WalkDrawStage.CellStatic, WalkDrawStage.BuildingShell };
        var blends = new[]
        {
            TranslucencyKind.Opaque, TranslucencyKind.AlphaBlend,
            TranslucencyKind.Additive, TranslucencyKind.InvAlpha,
        };
        var culls = new[] { CullMode.None, CullMode.Clockwise, CullMode.CounterClockwise };
        const int commandCount = 11;
        for (int i = 0; i < commandCount; i++)
        {
            stream.Append(MakeCommand(
                i,
                stage: stages[i % stages.Length],
                translucency: blends[i % blends.Length],
                cullMode: culls[i % culls.Length],
                detailCategory: i == 5 ? 1u : 0u));
        }

        PrepareAndDrawWhole(fx.Dispatcher, draw, stream);

        List<(int Start, int Count)> ranges = DecodeDrawRanges(fx.Device);
        int sum = ranges.Sum(r => r.Count);
        Assert.Equal(commandCount, sum);

        int coveredThrough = 0;
        foreach ((int start, int count) in ranges)
        {
            Assert.Equal(coveredThrough, start);
            coveredThrough += count;
        }
        Assert.Equal(commandCount, coveredThrough);
    }

    // ── Decode helpers ──────────────────────────────────────────────────────

    private static List<(int Start, int Count)> DecodeDrawRanges(RecordingGpuDevice device) =>
        [.. DecodeRuns(device).Select(r => (r.Start, r.Count))];

    private static List<(GpuPushConstants Constants, int Start, int Count)> DecodeRuns(
        RecordingGpuDevice device)
    {
        GpuPushConstants? lastConstants = null;
        uint? commandBase = null;
        var result = new List<(GpuPushConstants, int, int)>();
        foreach (var call in device.Calls)
        {
            if (call is GpuRecordedPushConstants pc)
            {
                lastConstants = pc.Constants;
            }
            else if (call is GpuRecordedMultiDrawIndirect mdi)
            {
                Assert.Equal((uint)WbDrawDispatcher.DrawCommandStride, mdi.StrideBytes);
                commandBase ??= mdi.OffsetBytes;
                int start = (int)((mdi.OffsetBytes - commandBase.Value) / mdi.StrideBytes);
                Assert.NotNull(lastConstants);
                result.Add((lastConstants!.Value, start, (int)mdi.DrawCount));
            }
        }
        return result;
    }

    // ── Fixture: a real WbDrawDispatcher against RecordingGpuDevice ─────────

    private readonly struct DrawScope : IDisposable
    {
        private readonly IDisposable _publication;
        private readonly IGpuPassEncoder _pass;

        public DrawScope(IGpuFrame frame, IGpuPassEncoder pass, IDisposable publication)
        {
            Frame = frame;
            _pass = pass;
            _publication = publication;
        }

        public IGpuFrame Frame { get; }

        public IGpuPassEncoder Pass => _pass;

        public void Dispose()
        {
            _publication.Dispose();
            _pass.Dispose();
        }
    }

    private sealed class DispatcherFixture : IDisposable
    {
        private readonly WbMeshAdapter _meshAdapter;
        private readonly TextureCache _textures;

        public DispatcherFixture()
        {
            Device = new RecordingGpuDevice();
            FrameLifetime = new GpuDeviceFrameLifetime(Device);
            Scope = new VulkanWorldPassScope(sampleCount: 1);
            _textures = new TextureCache(Device, new NoopDatReaderWriter());
            _meshAdapter = new WbMeshAdapter(
                Device,
                new NoopDatReaderWriter(),
                new NullPreparedAssetSource(),
                NullLogger<WbMeshAdapter>.Instance,
                Device.Retirement);
            var entitySpawnAdapter = new EntitySpawnAdapter(
                _textures,
                _ => throw new NotSupportedException(
                    "Not exercised by SubmitOrderedStream tests."));

            Dispatcher = new WbDrawDispatcher(
                Device,
                FrameLifetime,
                Scope,
                _textures,
                _meshAdapter,
                entitySpawnAdapter,
                new EntityClassificationCache(),
                new AcDream.Core.Rendering.TranslucencyFadeManager());
        }

        public RecordingGpuDevice Device { get; }

        public GpuDeviceFrameLifetime FrameLifetime { get; }

        public VulkanWorldPassScope Scope { get; }

        public WbDrawDispatcher Dispatcher { get; }

        /// <summary>Opens a frame and a backbuffer pass, publishes it on
        /// <see cref="Scope"/>, then clears the recorded calls so a test only
        /// sees what its own <c>SubmitOrderedStream</c> call produced.</summary>
        public DrawScope BeginDraw()
        {
            FrameLifetime.BeginFrame();
            IGpuFrame frame = FrameLifetime.CurrentFrame!;
            IGpuPassEncoder pass = frame.BeginPass(
                GpuPassDescription.BackbufferClear(
                    "fw2-ordered-stream-test", Vector4.Zero, sampleCount: 1));
            IDisposable publication = Scope.Publish(pass);
            Device.Clear();
            return new DrawScope(frame, pass, publication);
        }

        public void Dispose()
        {
            Dispatcher.Dispose();
            _meshAdapter.Dispose();
            _textures.Dispose();
            Device.Dispose();
        }
    }

    private sealed class NullPreparedAssetSource : IPreparedAssetSource
    {
        public PreparedAssetSourceStats Stats => default;

        public CacheStats DecodedTextureCacheStats => default;

        public PreparedAssetPresence Probe(
            AcDream.Content.Pak.PakAssetType type,
            uint sourceFileId) =>
            PreparedAssetPresence.Missing;

        public PreparedAssetReadResult Read(
            in PreparedAssetRequest request,
            CancellationToken cancellationToken = default) =>
            PreparedAssetReadResult.Missing;

        public void Dispose()
        {
        }
    }

    private sealed class NoopDatReaderWriter : IDatReaderWriter
    {
        private readonly StubDatabase _portal = new();
        private readonly StubDatabase _highRes = new();
        private readonly StubDatabase _language = new();
        private readonly StubDatabase _cell = new();

        public string SourceDirectory => string.Empty;

        public IDatDatabase Portal => _portal;

        public IDatDatabase Cell => _cell;

        public ReadOnlyDictionary<uint, IDatDatabase> CellRegions { get; } =
            new(new Dictionary<uint, IDatDatabase>());

        public IDatDatabase HighRes => _highRes;

        public IDatDatabase Language => _language;

        public IDatDatabase Local => _language;

        public ReadOnlyDictionary<uint, uint> RegionFileMap { get; } =
            new(new Dictionary<uint, uint>());

        public int PortalIteration => 0;

        public int CellIteration => 0;

        public int HighResIteration => 0;

        public int LanguageIteration => 0;

        public bool TryGetFileBytes(
            uint regionId,
            uint fileId,
            ref byte[] bytes,
            out int bytesRead)
        {
            bytesRead = 0;
            return false;
        }

        public IEnumerable<uint> GetAllIdsOfType<T>() where T : IDBObj =>
            Array.Empty<uint>();

        public IEnumerable<IDatReaderWriter.IdResolution> ResolveId(uint id) =>
            Array.Empty<IDatReaderWriter.IdResolution>();

        public bool TrySave<T>(T obj, int iteration = 0) where T : IDBObj =>
            throw new NotSupportedException();

        public bool TrySave<T>(
            uint regionId,
            T obj,
            int iteration = 0) where T : IDBObj =>
            throw new NotSupportedException();

        [return: MaybeNull]
        public T Get<T>(uint fileId) where T : IDBObj => default;

        public bool TryGet<T>(
            uint fileId,
            [MaybeNullWhen(false)] out T value) where T : IDBObj
        {
            value = default;
            return false;
        }

        public void Dispose()
        {
        }

        private sealed class StubDatabase : IDatDatabase
        {
            public DatDatabase Db => throw new NotSupportedException();

            public int Iteration => 0;

            public IEnumerable<uint> GetAllIdsOfType<T>() where T : IDBObj =>
                Array.Empty<uint>();

            public bool TryGet<T>(
                uint fileId,
                [MaybeNullWhen(false)] out T value) where T : IDBObj
            {
                value = default;
                return false;
            }

            public bool TryGetFileBytes(
                uint fileId,
                [MaybeNullWhen(false)] out byte[] value)
            {
                value = null;
                return false;
            }

            public bool TryGetFileBytes(
                uint fileId,
                ref byte[] bytes,
                out int bytesRead)
            {
                bytesRead = 0;
                return false;
            }

            public bool TrySave<T>(T obj, int iteration = 0) where T : IDBObj =>
                throw new NotSupportedException();

            public void Dispose()
            {
            }
        }
    }
}