using System;
using System.Collections.Generic;
using AcDream.Content;
using AcDream.Core.Meshing;
using AcDream.Core.Rendering;
using DatReaderWriter;
using DatReaderWriter.DBObjs;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Logging.Abstractions;
using Silk.NET.OpenGL;

namespace AcDream.App.Rendering.Wb;

/// <summary>
/// Single seam between acdream and WB's render pipeline. Owns the
/// <c>ObjectMeshManager</c> instance and exposes a stable acdream-shaped API
/// so the rest of the renderer doesn't need to know about WB's types directly.
///
/// <para>
/// As of Phase O-T7, all DAT I/O routes through the runtime-owned shared
/// <see cref="IDatReaderWriter"/> facade — the separate
/// <c>DefaultDatReaderWriter</c> file-handle set has been removed.
/// </para>
/// </summary>
public sealed class WbMeshAdapter : IDisposable, IWbMeshAdapter
{
    internal const int MaximumUploadsPerFrame = 8;
    internal const long MaximumUploadBytesPerFrame = 8L * 1024 * 1024;
    internal const long MaximumArrayAllocationBytesPerFrame = 8L * 1024 * 1024;
    internal const long MaximumMipmapBytesPerFrame = 8L * 1024 * 1024;
    internal const int MaximumNewArraysPerFrame = 1;
    internal const long MaximumBufferUploadBytesPerFrame = 8L * 1024 * 1024;
    // A GL buffer store is indivisible. The active vertex arena's explicit
    // supported ceiling is therefore the truthful one-allocation bound; only
    // its prefix copy is staged across frames.
    internal const long MaximumBufferAllocationBytesPerFrame =
        GlobalMeshBuffer.MaximumVertexBufferBytes;
    internal const long MaximumBufferCopyBytesPerFrame = 32L * 1024 * 1024;
    internal const int MaximumNewBuffersPerFrame = 1;
    internal const long MaximumSingleUploadBytes = 128L * 1024 * 1024;
    internal const long MaximumSingleArrayAllocationBytes = 128L * 1024 * 1024;
    internal const long MaximumSingleMipmapBytes = 128L * 1024 * 1024;
    internal const int MaximumSingleNewArrays = 16;
    internal const long MaximumSingleBufferUploadBytes = 32L * 1024 * 1024;
    internal const int MaximumReclaimedMeshesPerFrame = MaximumUploadsPerFrame;
    internal const long MaximumReclaimedMeshBytesPerFrame = 64L * 1024 * 1024;
    internal const int MaximumStaleDiscardsPerFrame = 64;
    private readonly OpenGLGraphicsDevice? _graphicsDevice;
    private readonly ObjectMeshManager? _meshManager;
    private readonly AcDream.App.Rendering.IGpuResourceRetirementQueue? _resourceRetirement;
    private readonly IDatReaderWriter? _dats;
    private readonly AcSurfaceMetadataTable _metadataTable = new();
    private readonly HashSet<ulong> _metadataPopulated = new();
    private readonly MeshUploadFrameBudget _uploadBudget = new(new MeshUploadBudgetLimits(
        MaximumUploadsPerFrame,
        MaximumUploadBytesPerFrame,
        MaximumArrayAllocationBytesPerFrame,
        MaximumMipmapBytesPerFrame,
        MaximumNewArraysPerFrame,
        MaximumBufferUploadBytesPerFrame,
        MaximumBufferAllocationBytesPerFrame,
        MaximumBufferCopyBytesPerFrame,
        MaximumNewBuffersPerFrame,
        MaximumSingleUploadBytes,
        MaximumSingleArrayAllocationBytes,
        MaximumSingleMipmapBytes,
        MaximumSingleNewArrays,
        MaximumSingleBufferUploadBytes));
    private readonly HashSet<TextureAtlasManager> _mipmapsBudgeted = new();

    /// <summary>
    /// True when this instance was created via <see cref="CreateUninitialized"/>;
    /// all public methods no-op when uninitialized.
    /// </summary>
    private readonly bool _isUninitialized;

    private bool _disposed;
    private AcDream.App.Rendering.OrderedResourceTeardown? _teardown;
    internal int LastUploadCount { get; private set; }
    internal long LastUploadBytes { get; private set; }
    internal int LastStaleDiscardCount { get; private set; }
    internal long LastArrayAllocationBytes { get; private set; }
    internal long LastPlannedMipmapBytes { get; private set; }
    internal int LastNewArrayCount { get; private set; }
    internal long LastBufferUploadBytes { get; private set; }
    internal long LastBufferAllocationBytes { get; private set; }
    internal long LastBufferCopyBytes { get; private set; }
    internal int LastNewBufferCount { get; private set; }
    internal int LastMipmapArrayCount { get; private set; }
    internal long LastMipmapBytes { get; private set; }
    internal int StagedUploadBacklog => _meshManager?.StagedMeshCount ?? 0;
    internal long StagedUploadBytes => _meshManager?.StagedMeshBytes ?? 0;
    internal bool StagingAtHighWater => _meshManager?.StagingAtHighWater ?? false;
    internal (int Count, long Bytes) CpuMeshCacheDiagnostics =>
        _meshManager?.CpuCacheDiagnostics ?? default;

    /// <summary>
    /// Constructs the full WB pipeline: OpenGLGraphicsDevice → shared bounded
    /// DAT facade → ObjectMeshManager.
    /// </summary>
    /// <param name="gl">Active Silk.NET GL context. Must be bound to the current
    /// thread (construction runs GL queries; call from OnLoad).</param>
    /// <param name="dats">acdream's shared runtime DAT facade, used to populate the surface
    /// metadata side-table via <c>GfxObjMesh.Build</c>. Shares file handles with
    /// the rest of the client; read-only access from the render thread.</param>
    /// <param name="logger">Logger for the adapter; ObjectMeshManager uses
    /// NullLogger internally.</param>
    public WbMeshAdapter(GL gl, IDatReaderWriter dats, ILogger<WbMeshAdapter> logger)
        : this(gl, dats, logger, AcDream.App.Rendering.ImmediateGpuResourceRetirementQueue.Instance)
    {
    }

    internal WbMeshAdapter(
        GL gl,
        IDatReaderWriter dats,
        ILogger<WbMeshAdapter> logger,
        AcDream.App.Rendering.IGpuResourceRetirementQueue resourceRetirement)
    {
        ArgumentNullException.ThrowIfNull(gl);
        ArgumentNullException.ThrowIfNull(dats);
        ArgumentNullException.ThrowIfNull(logger);

        _dats = dats;
        _resourceRetirement = resourceRetirement;
        _graphicsDevice = new OpenGLGraphicsDevice(
            gl,
            logger,
            new DebugRenderSettings(),
            resourceRetirement);
        _graphicsDevice.ParticleBatcher = new ParticleBatcher(_graphicsDevice);
        // ConsoleErrorLogger surfaces WB's silently-caught exceptions
        // (ObjectMeshManager.PrepareMeshData try/catch at line ~589).
        _meshManager = new ObjectMeshManager(
            _graphicsDevice,
            dats,
            new ConsoleErrorLogger<ObjectMeshManager>());
    }

    /// <summary>
    /// Minimal Console-backed logger that fires only on
    /// <see cref="LogLevel.Error"/> and above. Format:
    /// <code>[wb-error] &lt;message&gt;
    /// [wb-error]   &lt;ExceptionType&gt;: &lt;ExceptionMessage&gt;
    /// [wb-error]   at &lt;frame&gt; (up to 5 frames)</code>
    /// Used to surface WB's silently-caught exceptions in
    /// <c>ObjectMeshManager.PrepareMeshData</c>.
    /// </summary>
    private sealed class ConsoleErrorLogger<T> : ILogger<T>
    {
        public IDisposable BeginScope<TState>(TState state) where TState : notnull => NullScope.Instance;
        public bool IsEnabled(LogLevel logLevel) => logLevel >= LogLevel.Error;
        public void Log<TState>(
            LogLevel logLevel, EventId eventId, TState state, Exception? exception,
            Func<TState, Exception?, string> formatter)
        {
            if (!IsEnabled(logLevel)) return;
            var message = formatter(state, exception);
            Console.WriteLine($"[wb-error] {message}");
            if (exception is not null)
            {
                Console.WriteLine($"[wb-error]   {exception.GetType().Name}: {exception.Message}");
                var stack = (exception.StackTrace ?? "")
                    .Split(new[] { '\r', '\n' }, StringSplitOptions.RemoveEmptyEntries)
                    .Take(5);
                foreach (var s in stack) Console.WriteLine($"[wb-error]   {s.Trim()}");
            }
        }

        private sealed class NullScope : IDisposable
        {
            public static readonly NullScope Instance = new();
            public void Dispose() { }
        }
    }

    private WbMeshAdapter()
    {
        // Uninitialized constructor — only for tests / flag-off cases where
        // the caller wants a Dispose-safe no-op instance.
        _isUninitialized = true;
    }

    /// <summary>Test/init helper — produces a Dispose-safe instance with no
    /// underlying mesh manager. Public methods are all no-ops.</summary>
    public static WbMeshAdapter CreateUninitialized() => new();

    /// <summary>
    /// The surface metadata side-table populated on each first
    /// <see cref="IncrementRefCount"/>. Queried by the draw dispatcher
    /// to determine translucency, luminosity, and fog behavior per batch.
    /// </summary>
    public AcSurfaceMetadataTable MetadataTable => _metadataTable;

    /// <summary>
    /// Phase A8 (2026-05-28): exposes the underlying <see cref="ObjectMeshManager"/>
    /// so <c>EnvCellRenderer</c> can share the same global mesh buffer (VAO/VBO/IBO).
    /// Returns null when the adapter is uninitialized.
    /// </summary>
    public ObjectMeshManager? MeshManager => _meshManager;

    /// <summary>
    /// Returns the WB render data for <paramref name="id"/>, or null if not
    /// yet uploaded or if this adapter is uninitialized. Increments WB's
    /// internal usage counter — use <see cref="TryGetRenderData"/> for
    /// render-loop lookups that should not affect lifecycle.
    /// </summary>
    public ObjectRenderData? GetRenderData(ulong id)
    {
        if (_isUninitialized || _meshManager is null) return null;
        return _meshManager.GetRenderData(id);
    }

    /// <summary>
    /// Returns the WB render data for <paramref name="id"/> without
    /// modifying reference counts. Returns null if the mesh is not yet
    /// uploaded. Safe for render-loop lookups.
    /// </summary>
    public ObjectRenderData? TryGetRenderData(ulong id)
    {
        if (_isUninitialized || _meshManager is null) return null;
        return _meshManager.TryGetRenderData(id);
    }

    /// <inheritdoc/>
    public bool IsRenderDataReady(ulong id)
    {
        // An uninitialized adapter owns no render pipeline, so it must not
        // manufacture a readiness wait that can never complete. The modern
        // production path is always initialized at startup.
        return _isUninitialized || (_meshManager?.EnsureRenderDataReady(id) ?? false);
    }

    /// <inheritdoc/>
    public void IncrementRefCount(ulong id)
    {
        if (_isUninitialized || _meshManager is null) return;
        _meshManager.IncrementRefCount(id);

        bool metadataClaimed = false;
        try
        {
            metadataClaimed = _metadataPopulated.Add(id);
            if (metadataClaimed)
                PopulateMetadata(id);

        // WB's IncrementRefCount alone only bumps a usage counter; it does
        // NOT trigger mesh loading. We must explicitly call PrepareMeshDataAsync
        // so the background workers actually decode the GfxObj. The result
        // auto-enqueues into _stagedMeshData (ObjectMeshManager line 510),
        // which Tick() drains onto the GPU. Until that completes,
        // TryGetRenderData(id) returns null and the dispatcher silently
        // skips the entity — standard streaming flicker.
        //
        // #128 (2026-06-11): Prepare must RE-ARM whenever the id has no render
        // data — NOT only on the first-ever registration. The old
        // first-ever-only gate (`if (_metadataPopulated.Add(id))`) permanently
        // lost any id whose initial decode was cancelled before completing
        // (landblock unload → CancelStagedUploads during login/teleport
        // churn) or whose upload was later LRU-evicted: every subsequent
        // registration skipped Prepare, so the mesh stayed invisible for the
        // session with zero log output — the dispatcher's slow path just
        // counted meshMissing forever (issue #55's 1.45M/5s mountain was this
        // bug's heartbeat). User-visible: the AAB3 tower staircase rendering
        // partially or not at all depending on the session's landblock
        // load/unload interleaving (#119/#128 "broken stairs"). Safe to call
        // unconditionally when data is absent: PrepareMeshDataAsync early-outs
        // on existing render data, returns the in-flight task when already
        // pending, and dedups via _preparationTasks.
        //
        // isSetup: false — acdream's MeshRefs already carry expanded
        // per-part GfxObj ids (0x01XXXXXX). WB's Setup-expansion path is
        // unused.
            if (metadataClaimed || _meshManager.TryGetRenderData(id) is null)
                _meshManager.PrepareMeshDataAsync(id, isSetup: false);
        }
        catch (Exception acquireFailure)
        {
            if (metadataClaimed)
            {
                _metadataPopulated.Remove(id);
                _metadataTable.Remove(id);
            }

            // IncrementRefCount is a public ownership boundary. Metadata/DAT
            // preparation happens after ObjectMeshManager commits its count,
            // so compensate before reporting failure. ObjectMeshManager's
            // decrement has a strong exception guarantee; if compensation
            // itself fails, expose that the increment remains committed so a
            // higher-level transactional owner can retain its held marker.
            try
            {
                _meshManager.DecrementRefCount(id);
            }
            catch (Exception rollbackFailure)
            {
                throw new MeshReferenceMutationException(
                    $"Mesh 0x{id:X10} reference acquisition failed and its committed increment could not be rolled back.",
                    mutationCommitted: true,
                    new AggregateException(acquireFailure, rollbackFailure));
            }

            throw;
        }
    }

    /// <inheritdoc/>
    public void DecrementRefCount(ulong id)
    {
        if (_isUninitialized || _meshManager is null) return;
        _meshManager.DecrementRefCount(id);
    }

    /// <inheritdoc/>
    public void PinPreparedRenderData(ulong id)
    {
        if (_isUninitialized || _meshManager is null) return;
        // EnvCell geometry has its own schema-aware preparation request.
        // Only establish lifecycle ownership here; IncrementRefCount's normal
        // generic GfxObj preparation would decode the synthetic id incorrectly.
        _meshManager.IncrementRefCount(id);
    }

    /// <summary>
    /// #128 self-heal (2026-06-11): re-request a mesh load at the POINT OF
    /// USE. Registration-time re-arming was insufficient — a preparation
    /// cancelled by landblock churn AFTER the last registration event
    /// (running across blocks loads/unloads them repeatedly) left the mesh
    /// permanently unloadable with no later event to re-fire it. The draw
    /// dispatcher touches every missing-but-referenced mesh every frame (the
    /// meshMissing slow path) — that is the one place a retry can never be
    /// missed. Cheap and idempotent: PrepareMeshDataAsync early-outs on
    /// existing render data and returns the in-flight task when pending.
    /// Retail-equivalence: retail loads content synchronously — geometry is
    /// never permanently absent; this converges our async pipeline to the
    /// same guarantee.
    /// </summary>
    public void EnsureLoaded(ulong id)
    {
        if (_isUninitialized || _meshManager is null) return;
        _meshManager.PrepareMeshDataAsync(id, isSetup: false);
    }

    /// <summary>
    /// Per-frame drain of the WB pipeline's main-thread work queues. MUST be
    /// called once per frame from the render thread. Without this, the staged
    /// mesh data queue grows unbounded (memory leak) and queued GL actions
    /// never execute.
    ///
    /// <para>
    /// Order matters: <c>ProcessGLQueue</c> runs first to apply any pending GL
    /// state changes (e.g., texture uploads queued by background workers
    /// during mesh prep). Then we drain staged mesh data, calling
    /// <c>UploadMeshData</c> on each item to materialize the actual GL VAO /
    /// VBO / IBO resources. After Tick, <c>GetRenderData</c> for any id
    /// previously passed to <c>IncrementRefCount</c> may return non-null.
    /// </para>
    ///
    /// <para>
    /// No-op when the adapter is uninitialized (e.g., flag is off and the
    /// adapter was constructed via <c>CreateUninitialized</c>).
    /// </para>
    /// </summary>
    public void Tick()
    {
        if (_isUninitialized) return;
        if (_disposed) return;

        ObjectMeshManager meshManager = _meshManager!;
        _graphicsDevice!.ProcessGLQueue();
        // #125: drain staged uploads; a FAILED upload (UploadMeshData returned
        // null from its catch) is re-staged for a LATER frame, not dropped. The
        // re-stages are collected and re-enqueued AFTER the loop — re-enqueuing
        // inside the while would let a deterministic failure spin the queue in a
        // single frame. UploadOrRequeue bounds the retries (MaxUploadRetries) so
        // a genuine defect surfaces loudly instead of the old silent sticky drop.
        List<MeshUploadQueueItem>? requeue = null;
        _uploadBudget.Reset();
        _mipmapsBudgeted.Clear();
        int staleDiscardCount = 0;
        bool arenaBackpressured = false;
        GlobalMeshBuffer? globalBuffer = meshManager.GlobalBuffer;

        // A backing-store migration is real GL work, not a cost estimate. One
        // bounded copy chunk runs per frame while the old VAO remains active.
        // Uploads stay queued until the atomic final swap has completed.
        if (globalBuffer?.IsMigrationInProgress == true)
        {
            GlobalMeshMaintenanceStep maintenance =
                globalBuffer.AdvanceMigration(MaximumBufferCopyBytesPerFrame);
            _uploadBudget.RecordBufferMaintenance(
                maintenance.AllocationBytes,
                maintenance.CopyBytes,
                maintenance.NewBufferCount);
            arenaBackpressured = !maintenance.Completed;
        }

        while (globalBuffer?.IsMigrationInProgress != true
            && _uploadBudget.BufferCopyBytes == 0
            && _uploadBudget.ObjectCount < MaximumUploadsPerFrame)
        {
            staleDiscardCount += meshManager.DiscardUnownedStagedPrefix(
                MaximumStaleDiscardsPerFrame - staleDiscardCount);
            if (staleDiscardCount >= MaximumStaleDiscardsPerFrame)
                break;
            if (!meshManager.TryPeekStagedMeshData(out MeshUploadQueueItem next))
                break;

            GlobalMeshCapacityResult capacity;
            GlobalMeshMaintenanceStep maintenance;
            try
            {
                capacity = meshManager.EnsureGlobalBufferCapacity(next, out maintenance);
            }
            catch (NotSupportedException error)
            {
                RejectUnsupportedHead(meshManager, next, error);
                throw;
            }
            if (capacity == GlobalMeshCapacityResult.MigrationStarted)
            {
                _uploadBudget.RecordBufferMaintenance(
                    maintenance.AllocationBytes,
                    maintenance.CopyBytes,
                    maintenance.NewBufferCount);
                arenaBackpressured = true;
                break;
            }
            if (capacity == GlobalMeshCapacityResult.MigrationInProgress)
            {
                arenaBackpressured = true;
                break;
            }
            if (capacity == GlobalMeshCapacityResult.NeedsReclamation)
            {
                // Do not evict another batch while the frame-fence queue is
                // already returning ranges or retiring an old backing store.
                // Waiting for real allocator state prevents three frames of
                // duplicate eviction before the first release becomes reusable.
                if (globalBuffer?.HasPendingReclamation != true)
                {
                    var reclaimed = meshManager.ReclaimUnusedResources(
                        MaximumReclaimedMeshesPerFrame,
                        MaximumReclaimedMeshBytesPerFrame,
                        forceArenaReclamation: true);
                    if (reclaimed.Count == 0)
                    {
                        throw new NotSupportedException(
                            $"The live global-mesh working set cannot fit the supported "
                            + $"{GlobalMeshBuffer.MaximumVertexBufferBytes + GlobalMeshBuffer.MaximumIndexBufferBytes:N0}-byte arena "
                            + $"(blocked staging generation {next.Generation}, object 0x{next.Data.ObjectId:X10}).");
                    }
                }
                arenaBackpressured = true;
                break;
            }

            MeshUploadCost cost;
            try
            {
                cost = meshManager.PlanUploadCost(
                    next.Data,
                    _mipmapsBudgeted,
                    next.Generation);
                if (!_uploadBudget.TryAdmit(cost))
                    break;
            }
            catch (NotSupportedException error)
            {
                RejectUnsupportedHead(meshManager, next, error);
                throw;
            }

            if (!meshManager.TryDequeueStagedMeshData(out MeshUploadQueueItem meshData))
                break;
            if (meshData.Generation != next.Generation)
                throw new InvalidOperationException("The staged mesh FIFO head changed during render-thread admission.");
            if (meshManager.UploadOrRequeue(meshData))
                (requeue ??= new()).Add(meshData);
            meshManager.AddDirtyAtlasesTo(_mipmapsBudgeted);
        }
        if (requeue is not null)
            foreach (var m in requeue)
                meshManager.RequeueStagedMeshData(m);
        meshManager.SetArenaBackpressure(arenaBackpressured);

        bool texProbe = AcDream.Core.Rendering.RenderingDiagnostics.ProbeTexFlushEnabled;
        var pendingBefore = texProbe
            ? meshManager.GetPendingTextureUpdateStats()
            : default;

        // #105 root cause (2026-06-10): TextureAtlasManager.AddTexture only STAGES
        // immutable decoded payloads in ManagedGLTextureArray._pendingUpdates — the
        // actual TexSubImage3D copies + mipmap regeneration happen in
        // ProcessDirtyUpdates, which WB drives ONCE PER FRAME from its render loop
        // (WB GameScene.cs:975 `_meshManager?.GenerateMipmaps()`, just before the
        // opaque pass). That call site lived in the GameScene file the N.4/O-T4
        // extraction replaced with GameWindow, so the driver was silently dropped:
        // staged updates never reached TexSubImage3D, leaving undefined
        // TexStorage3D content behind valid resident bindless handles — the
        // intermittent white indoor walls (#105). Pre-fix evidence: 126 updates
        // stuck across 34/34 arrays at standstill (texflush-prefix.log). Tick()
        // runs before all draw passes (GameWindow OnRender), so this is the exact
        // WB-equivalent position.
        (LastMipmapArrayCount, LastMipmapBytes) = meshManager.GenerateMipmaps();
        if (globalBuffer?.HasPendingReclamation != true)
        {
            meshManager.ReclaimUnusedResources(
                MaximumReclaimedMeshesPerFrame,
                MaximumReclaimedMeshBytesPerFrame);
        }
        meshManager.EvictOneEmptyAtlas();

        // Arena maintenance is capacity-driven and uses genuinely idle upload
        // frames. It never competes with destination materialization, and the
        // GlobalMeshBuffer policy retains enough hysteresis that portal-route
        // revisits do not alternate shrink/grow every frame.
        if (_uploadBudget.ObjectCount == 0
            && LastMipmapArrayCount == 0
            && meshManager.StagedMeshCount == 0
            && globalBuffer?.IsMigrationInProgress == false
            && globalBuffer.TryTrimUnusedTail(out GlobalMeshMaintenanceStep trim))
        {
            _uploadBudget.RecordBufferMaintenance(
                trim.AllocationBytes,
                trim.CopyBytes,
                trim.NewBufferCount);
            meshManager.SetArenaBackpressure(true);
        }

        LastUploadCount = _uploadBudget.ObjectCount;
        LastUploadBytes = _uploadBudget.SourceBytes;
        LastStaleDiscardCount = staleDiscardCount;
        LastArrayAllocationBytes = _uploadBudget.ArrayAllocationBytes;
        LastPlannedMipmapBytes = _uploadBudget.MipmapBytes;
        LastNewArrayCount = _uploadBudget.NewArrayCount;
        LastBufferUploadBytes = _uploadBudget.BufferUploadBytes;
        LastBufferAllocationBytes = _uploadBudget.BufferAllocationBytes;
        LastBufferCopyBytes = _uploadBudget.BufferCopyBytes;
        LastNewBufferCount = _uploadBudget.NewBufferCount;

        if (texProbe)
            EmitTexFlushProbe(pendingBefore);
    }

    private static void RejectUnsupportedHead(
        ObjectMeshManager meshManager,
        MeshUploadQueueItem expected,
        NotSupportedException error)
    {
        if (!meshManager.TryDequeueStagedMeshData(out MeshUploadQueueItem rejected)
            || rejected.Generation != expected.Generation)
        {
            throw new InvalidOperationException(
                "The staged mesh FIFO head changed while rejecting an unsupported generation.",
                error);
        }
        meshManager.RejectUnsupportedStagedUpload(rejected, error);
    }

    // #105 apparatus state — see RenderingDiagnostics.ProbeTexFlushEnabled.
    private int _lastTexFlushBefore = -1;
    private int _texFlushHeartbeat;

    /// <summary>
    /// #105 apparatus: one <c>[tex-flush]</c> line on change of the staged-texture
    /// pending picture (plus a ~10 s heartbeat while anything is stuck). A healthy
    /// frame ends with <c>after=0</c>; <c>before==after&gt;0</c> persisting at
    /// standstill is the white-walls mechanism live (staged uploads never applied).
    /// </summary>
    private void EmitTexFlushProbe((int PendingUpdates, int ArraysWithPending, int TotalArrays) before)
    {
        var after = _meshManager!.GetPendingTextureUpdateStats();
        bool changed = before.PendingUpdates != _lastTexFlushBefore;
        bool flushed = after.PendingUpdates != before.PendingUpdates;
        bool heartbeat = after.PendingUpdates > 0 && ++_texFlushHeartbeat >= 600;
        if (!changed && !flushed && !heartbeat) return;

        _texFlushHeartbeat = 0;
        _lastTexFlushBefore = before.PendingUpdates;
        Console.WriteLine(
            $"[tex-flush] before={before.PendingUpdates} after={after.PendingUpdates}" +
            $" arrays={after.ArraysWithPending}/{after.TotalArrays}" +
            $" (arraysBefore={before.ArraysWithPending})");
    }

    private void PopulateMetadata(ulong id)
    {
        if (_dats is null) return;
        if (!_dats.Portal.TryGet<GfxObj>((uint)id, out var gfxObj)) return;

        var subMeshes = GfxObjMesh.Build(gfxObj, _dats);
        for (int i = 0; i < subMeshes.Count; i++)
        {
            var sm = subMeshes[i];
            _metadataTable.Add(id, i, new AcSurfaceMetadata(
                sm.Translucency, sm.Luminosity, sm.Diffuse,
                sm.SurfOpacity, sm.NeedsUvRepeat, sm.DisableFog));
        }
    }

    /// <inheritdoc/>
    public void Dispose()
    {
        if (_disposed)
            return;

        // These are dependency edges, not merely a best-effort cleanup list.
        // In particular, the sampler objects owned by the device must remain
        // alive until every resident texture-array handle has been retired.
        _teardown ??= new AcDream.App.Rendering.OrderedResourceTeardown(
            () =>
            {
                // The current global arena is still directly owned by the mesh
                // manager. Fence every submitted draw before manager teardown
                // can delete that arena's VAO/VBO/IBO.
                if (_resourceRetirement is AcDream.App.Rendering.GpuFrameFlightController frameFlights)
                    frameFlights.WaitForSubmittedWork();
            },
            () => _meshManager?.Dispose(),
            () => DrainGraphicsQueue("publishing mesh resource retirements"),
            () =>
            {
                if (_resourceRetirement is AcDream.App.Rendering.GpuFrameFlightController frameFlights)
                    frameFlights.WaitForSubmittedWork();
            },
            () => DrainGraphicsQueue("releasing retired mesh resources"),
            () => _graphicsDevice?.Dispose(),
            () => DrainGraphicsQueue("deleting mesh graphics-device resources"));

        _teardown.Advance();
        _disposed = _teardown.IsComplete;
    }

    private void DrainGraphicsQueue(string operation)
    {
        if (_graphicsDevice is null)
            return;

        _graphicsDevice.ProcessGLQueue();
        if (_graphicsDevice.HasPendingGLWork)
        {
            throw new InvalidOperationException(
                $"OpenGL work remains pending after {operation}; retry adapter disposal to continue the exact stage.");
        }
    }
}