// src/AcDream.App/Rendering/TextureCache.cs
using AcDream.Core.Textures;
using AcDream.Core.World;
using AcDream.Content;
using DatReaderWriter;
using DatReaderWriter.DBObjs;
using Silk.NET.OpenGL;
using System.Linq;
using PixelFormatId = DatReaderWriter.Enums.PixelFormat;
using SurfaceType = DatReaderWriter.Enums.SurfaceType;

namespace AcDream.App.Rendering;

public sealed unsafe class TextureCache : Wb.IEntityTextureLifetime, IDisposable
{
    private readonly GL _gl;
    private readonly IDatReaderWriter _dats;
    // Handle and decoded dimensions are one atomic cache entry. Keeping them
    // in separate dictionaries allowed GetOrUpload(surfaceId) followed by the
    // sized overload to upload a second GL texture and orphan the first.
    private readonly Dictionary<uint, (uint Handle, int Width, int Height)>
        _surfacesById = new();
    private readonly Dictionary<(uint SurfaceId, uint OrigTextureId), (int Width, int Height)>
        _decodedDimensionsByTexture = new();
    private uint _magentaHandle;

    // Direct-RenderSurface caches for UI sprites: 0x06xxxxxx RenderSurface ids
    // decoded directly (Portal/HighRes → DecodeRenderSurface), bypassing the
    // Surface→SurfaceTexture chain that GetOrUpload uses for world materials.
    private readonly Dictionary<uint, uint> _handlesByRenderSurfaceId = new();
    private readonly Dictionary<uint, (int w, int h)> _rsSizeById = new();

    // Ad-hoc handles produced by the public UploadRgba8(byte[],int,int,bool) wrapper
    // (used by IconComposer for composited item icons). These are NOT stored in any
    // of the keyed caches above, so Dispose must sweep this list to avoid leaking
    // GL texture objects until process exit.
    private readonly List<uint> _adhocHandles = new();

    private readonly Wb.BindlessSupport? _bindless;
    private readonly CompositeTextureArrayCache? _compositeTextures;

    // Standalone Texture2DArray caches. Shared world surfaces use WB's atlas;
    // this base cache remains for consumers such as particle rendering.
    // Per-entity override composites are owner-scoped but share pooled array
    // storage. Retail CSurface ownership releases immediately while ImgTex
    // residency remains separately purgeable; CompositeTextureArrayCache
    // mirrors that split without one GL object per material composite.
    private readonly StandaloneBindlessTextureCache? _particleTextures;
    private readonly Dictionary<(uint surfaceId, uint origTexOverride), bool> _paletteIndexedByTexture = new();

    internal int OwnedBindlessTextureCount => _compositeTextures?.ActiveResourceCount ?? 0;
    internal int TextureOwnerCount => _compositeTextures?.OwnerCount ?? 0;
    internal int CachedCompositeTextureCount => _compositeTextures?.CachedEntryCount ?? 0;
    internal int CachedUnownedCompositeCount => _compositeTextures?.UnownedEntryCount ?? 0;
    internal long CachedUnownedCompositeBytes => _compositeTextures?.UnownedBytes ?? 0;
    internal int CompositeAtlasCount => _compositeTextures?.AtlasCount ?? 0;
    internal long CompositeAtlasBytes => _compositeTextures?.AllocatedBytes ?? 0;
    internal int CompositeFrameUploadCount => _compositeTextures?.FrameUploadCount ?? 0;
    internal long CompositeFrameUploadBytes => _compositeTextures?.FrameUploadBytes ?? 0;
    internal bool CanStartCompositeUpload => _compositeTextures?.CanStartUpload == true;
    internal int CachedParticleTextureCount => _particleTextures?.EntryCount ?? 0;
    internal int ActiveParticleTextureCount => _particleTextures?.ActiveResourceCount ?? 0;
    internal int ParticleTextureOwnerCount => _particleTextures?.OwnerCount ?? 0;
    internal int CachedUnownedParticleTextureCount => _particleTextures?.UnownedEntryCount ?? 0;
    internal long CachedUnownedParticleTextureBytes => _particleTextures?.UnownedBytes ?? 0;

    // Phase N.6 slice 1 (2026-05-11): per-upload metadata for the
    // ACDREAM_DUMP_SURFACES=1 histogram dump path. Populated at upload
    // time so the dump method doesn't have to query GL state. Keyed by
    // GL texture name (same key used in cache value tuples). Format
    // label is "RGBA8_DECODED" for the post-decode upload (all uploads
    // currently land as RGBA8 regardless of source format).
    private readonly Dictionary<uint, (int Width, int Height, string Format)> _uploadMetadata = new();

    // Frame counter for the one-shot ACDREAM_DUMP_SURFACES=1 trigger.
    // Increments per Tick call; fires the dump once at frame index 600
    // and never again for the session. See spec §5.
    private int _dumpFrameCounter;
    private bool _surfaceHistogramAlreadyDumped;

    public TextureCache(GL gl, IDatReaderWriter dats, Wb.BindlessSupport? bindless = null)
        : this(gl, dats, bindless, ImmediateGpuResourceRetirementQueue.Instance)
    {
    }

    internal TextureCache(
        GL gl,
        IDatReaderWriter dats,
        Wb.BindlessSupport? bindless,
        IGpuResourceRetirementQueue retirementQueue)
    {
        _gl = gl;
        _dats = dats;
        _bindless = bindless;
        ArgumentNullException.ThrowIfNull(retirementQueue);
        if (bindless is not null)
        {
            _compositeTextures = new CompositeTextureArrayCache(gl, bindless, retirementQueue);
            _particleTextures = new StandaloneBindlessTextureCache(
                new ParticleTextureBackend(this),
                retirementQueue);
        }
    }

    /// <summary>
    /// Get or upload the GL texture handle for a Surface id. Returns a
    /// 1x1 magenta fallback if the Surface or its RenderSurface chain is
    /// missing or uses an unsupported format.
    /// </summary>
    public uint GetOrUpload(uint surfaceId)
        => GetOrUploadSurfaceCore(surfaceId, out _, out _);

    /// <summary>
    /// Like <see cref="GetOrUpload(uint)"/> but also returns the decoded
    /// pixel dimensions. UI 9-slice geometry needs the source size to
    /// compute slice UVs. Cached alongside the handle.
    /// </summary>
    public uint GetOrUpload(uint surfaceId, out int width, out int height)
        => GetOrUploadSurfaceCore(surfaceId, out width, out height);

    private uint GetOrUploadSurfaceCore(uint surfaceId, out int width, out int height)
    {
        if (_surfacesById.TryGetValue(surfaceId, out var existing))
        {
            width = existing.Width;
            height = existing.Height;
            return existing.Handle;
        }

        DecodedTexture decoded = DecodeFromDats(
            surfaceId,
            origTextureOverride: null,
            paletteOverride: null);
        if (System.Environment.GetEnvironmentVariable("ACDREAM_DUMP_SKY") == "1")
            DumpAlphaHistogram(surfaceId, decoded);
        uint h = UploadRgba8(decoded);
        _surfacesById.Add(surfaceId, (h, decoded.Width, decoded.Height));
        width = decoded.Width;
        height = decoded.Height;
        return h;
    }

    /// <summary>
    /// Upload a UI sprite by its RenderSurface DataId (0x06xxxxxx), decoded
    /// DIRECTLY (Portal/HighRes → DecodeRenderSurface) rather than through the
    /// Surface→SurfaceTexture chain that <see cref="GetOrUpload(uint)"/> uses
    /// for world-geometry materials. This is the correct path for retail UI
    /// chrome + font glyph sheets, which reference RenderSurface directly.
    /// Paletted (PFID_P8 / PFID_INDEX16) UI sprites — e.g. the selected-object
    /// health-bar track 0x0600193E — are decoded against the RenderSurface's own
    /// <c>DefaultPaletteId</c> (same starting palette <see cref="DecodeFromDats"/>
    /// uses); non-paletted formats have DefaultPaletteId==0 → palette null. Returns
    /// a 1x1 magenta handle on miss.
    /// </summary>
    public uint GetOrUploadRenderSurface(uint renderSurfaceId, out int width, out int height, bool nearest = false)
    {
        if (_handlesByRenderSurfaceId.TryGetValue(renderSurfaceId, out var existing)
            && _rsSizeById.TryGetValue(renderSurfaceId, out var sz))
        {
            width = sz.w; height = sz.h;
            return existing;
        }

        DecodedTexture decoded;
        if (_dats.Portal.TryGet<RenderSurface>(renderSurfaceId, out var rs)
            || _dats.HighRes.TryGet<RenderSurface>(renderSurfaceId, out rs))
        {
            // Resolve the surface's own default palette so paletted UI sprites decode
            // correctly instead of the magenta fallback (the back-track 0x0600193E behind
            // the selected-object health bar is PFID_P8/INDEX16). Non-paletted formats
            // (DefaultPaletteId==0) keep the previous null-palette behaviour unchanged.
            Palette? palette = rs.DefaultPaletteId != 0
                ? _dats.Get<Palette>(rs.DefaultPaletteId)
                : null;
            decoded = SurfaceDecoder.DecodeRenderSurface(rs, palette);
        }
        else
        {
            decoded = DecodedTexture.Magenta;
        }

        uint h = UploadRgba8(decoded, nearest);
        _handlesByRenderSurfaceId[renderSurfaceId] = h;
        _rsSizeById[renderSurfaceId] = (decoded.Width, decoded.Height);
        width = decoded.Width; height = decoded.Height;
        return h;
    }

    /// <summary>
    /// Alpha-channel histogram for one decoded texture. Used to diagnose
    /// "why are clouds not transparent" — if cloud textures come out with
    /// alpha = 1.0 everywhere we know the decode path strips the alpha
    /// channel somewhere. Printed once per unique surfaceId under
    /// <c>ACDREAM_DUMP_SKY=1</c>. Adds ~2ms per texture upload, negligible.
    /// </summary>
    private static void DumpAlphaHistogram(uint surfaceId, DecodedTexture decoded)
    {
        if (decoded.Rgba8.Length == 0 || decoded.Width == 0 || decoded.Height == 0)
        {
            System.Console.WriteLine($"[tex-alpha] surf=0x{surfaceId:X8} empty");
            return;
        }
        int total = decoded.Rgba8.Length / 4;
        // Bucket alpha in 10 bins.
        var buckets = new int[10];
        int aMin = 255, aMax = 0;
        long aSum = 0;
        for (int i = 0; i < decoded.Rgba8.Length; i += 4)
        {
            int a = decoded.Rgba8[i + 3];
            if (a < aMin) aMin = a;
            if (a > aMax) aMax = a;
            aSum += a;
            int b = a * 10 / 256;
            if (b > 9) b = 9;
            buckets[b]++;
        }
        float aMean = aSum / (float)total / 255f;
        var pct = new string[10];
        for (int i = 0; i < 10; i++) pct[i] = $"{100.0 * buckets[i] / total:F0}%";
        System.Console.WriteLine(
            $"[tex-alpha] surf=0x{surfaceId:X8} {decoded.Width}x{decoded.Height} " +
            $"a_min={aMin / 255f:F3} a_max={aMax / 255f:F3} a_mean={aMean:F3} " +
            $"bins[0-9]={string.Join(",", pct)}");
    }

    /// <summary>
    /// Acquires the exact DAT-decoded one-layer texture array for a live
    /// particle emitter. Equivalent surfaces are shared; the cache ownership
    /// ends with <see cref="ReleaseParticleTextureOwner"/>.
    /// </summary>
    internal ulong AcquireParticleTexture(int emitterHandle, uint surfaceId)
    {
        ArgumentOutOfRangeException.ThrowIfNegativeOrZero(emitterHandle);
        ArgumentOutOfRangeException.ThrowIfZero(surfaceId);
        StandaloneBindlessTextureCache textures = EnsureParticleTexturesAvailable();
        uint ownerId = checked((uint)emitterHandle);
        if (textures.TryAcquire(
                ownerId,
                surfaceId,
                out StandaloneBindlessTextureResource? existing))
        {
            return existing.Handle;
        }

        DecodedTexture decoded = DecodeFromDats(
            surfaceId,
            origTextureOverride: null,
            paletteOverride: null);
        uint name = UploadRgba8AsLayer1Array(decoded);
        ulong handle = 0;
        try
        {
            handle = _bindless!.GetResidentHandle(name);
            Wb.GLHelpers.ThrowOnResourceError(
                _gl,
                $"making particle surface 0x{surfaceId:X8} resident");
            var resource = new StandaloneBindlessTextureResource
            {
                SurfaceId = surfaceId,
                Name = name,
                Handle = handle,
                Bytes = checked((long)decoded.Width * decoded.Height * 4L),
            };
            textures.AddAndAcquire(ownerId, resource);
            return handle;
        }
        catch (Exception residencyFailure)
        {
            List<Exception>? cleanupFailures = null;
            void Attempt(Action cleanup)
            {
                try { cleanup(); }
                catch (Exception ex) { (cleanupFailures ??= []).Add(ex); }
            }

            bool residencyReleased = handle == 0;
            if (handle != 0)
            {
                Attempt(() =>
                {
                    _bindless!.MakeNonResident(handle);
                    Wb.GLHelpers.ThrowOnResourceError(
                        _gl,
                        "rolling back particle texture residency");
                    residencyReleased = true;
                });
            }
            if (residencyReleased)
                Attempt(() => DeleteUploadedTexture(name));
            if (cleanupFailures is not null)
            {
                cleanupFailures.Insert(0, residencyFailure);
                throw new AggregateException(
                    "Particle texture residency and rollback both failed.",
                    cleanupFailures);
            }
            throw;
        }
    }

    internal void ReleaseParticleTextureOwner(int emitterHandle)
    {
        if (emitterHandle <= 0 || _particleTextures is null)
            return;
        _particleTextures.ReleaseOwner(checked((uint)emitterHandle));
    }

    /// <summary>
    /// Owner-scoped bindless variant for a server-supplied original-texture
    /// replacement. Stores compatible composites in a pooled Texture2DArray
    /// and returns its resident handle plus the assigned layer. Equivalent
    /// composites are shared until their final live owner leaves. Throws if
    /// BindlessSupport wasn't provided.
    /// </summary>
    internal BindlessTextureLocation GetOrUploadWithOrigTextureOverrideBindless(
        uint ownerLocalId,
        uint surfaceId,
        uint overrideOrigTextureId)
    {
        CompositeTextureArrayCache composites = EnsureCompositeTexturesAvailable();
        var key = new CompositeTextureKey(
            CompositeTextureKind.OriginalTextureOverride,
            surfaceId,
            overrideOrigTextureId,
            Palette: default);
        if (composites.TryAcquire(ownerLocalId, key, out BindlessTextureLocation existing))
            return existing;
        if (!composites.CanStartUpload)
            return default;
        (int width, int height) = ResolveDecodedDimensions(surfaceId, overrideOrigTextureId);
        if (!composites.CanPrepareUpload(width, height))
            return default;

        DecodedTexture decoded = DecodeFromDats(
            surfaceId,
            origTextureOverride: overrideOrigTextureId,
            paletteOverride: null);
        return composites.TryAddAndAcquire(ownerLocalId, key, decoded, out BindlessTextureLocation added)
            ? added
            : default;
    }

    /// <summary>
    /// Owner-scoped bindless palette composite. Applies the palette override on
    /// top of the texture's default palette before decoding, stores compatible
    /// composites in a pooled Texture2DArray, and returns its resident handle
    /// plus the assigned layer. Structural identity is computed once per entity.
    /// Throws if BindlessSupport wasn't provided to the constructor.
    /// </summary>
    internal BindlessTextureLocation GetOrUploadWithPaletteOverrideBindless(
        uint ownerLocalId,
        uint surfaceId,
        uint? overrideOrigTextureId,
        PaletteOverride paletteOverride,
        PaletteCompositeIdentity paletteIdentity)
    {
        CompositeTextureArrayCache composites = EnsureCompositeTexturesAvailable();
        uint origTexKey = overrideOrigTextureId ?? 0;
        var key = new CompositeTextureKey(
            CompositeTextureKind.PaletteComposite,
            surfaceId,
            origTexKey,
            paletteIdentity);
        if (composites.TryAcquire(ownerLocalId, key, out BindlessTextureLocation existing))
            return existing;
        if (!composites.CanStartUpload)
            return default;
        (int width, int height) = ResolveDecodedDimensions(surfaceId, overrideOrigTextureId);
        if (!composites.CanPrepareUpload(width, height))
            return default;

        DecodedTexture decoded = DecodeFromDats(
            surfaceId,
            origTextureOverride: overrideOrigTextureId,
            paletteOverride: paletteOverride);
        return composites.TryAddAndAcquire(ownerLocalId, key, decoded, out BindlessTextureLocation added)
            ? added
            : default;
    }

    /// <summary>
    /// Retail applies a palette composite only to P8/INDEX16 image data.
    /// Cache the resolved source format so animated entities do not reopen the
    /// DAT chain every frame.
    /// </summary>
    internal bool IsPaletteIndexed(uint surfaceId, uint? overrideOrigTextureId)
    {
        uint origTexKey = overrideOrigTextureId ?? 0;
        var key = (surfaceId, origTexKey);
        if (_paletteIndexedByTexture.TryGetValue(key, out bool indexed))
            return indexed;

        Surface? surface = _dats.Get<Surface>(surfaceId);
        if (surface is null || surface.Type.HasFlag(SurfaceType.Base1Solid))
            return _paletteIndexedByTexture[key] = false;

        uint surfaceTextureId = overrideOrigTextureId ?? (uint)surface.OrigTextureId;
        SurfaceTexture? texture = _dats.Get<SurfaceTexture>(surfaceTextureId);
        if (texture is null || texture.Textures.Count == 0)
            return _paletteIndexedByTexture[key] = false;

        uint renderSurfaceId = (uint)texture.Textures[0];
        if (!_dats.Portal.TryGet<RenderSurface>(renderSurfaceId, out RenderSurface? renderSurface)
            && !_dats.HighRes.TryGet<RenderSurface>(renderSurfaceId, out renderSurface))
            return _paletteIndexedByTexture[key] = false;

        indexed = renderSurface.Format is PixelFormatId.PFID_P8 or PixelFormatId.PFID_INDEX16;
        _paletteIndexedByTexture[key] = indexed;
        return indexed;
    }

    private (int Width, int Height) ResolveDecodedDimensions(
        uint surfaceId,
        uint? overrideOrigTextureId)
    {
        var key = (surfaceId, overrideOrigTextureId ?? 0);
        if (_decodedDimensionsByTexture.TryGetValue(key, out var cached))
            return cached;

        Surface? surface = _dats.Get<Surface>(surfaceId);
        if (surface is null
            || surface.Type.HasFlag(SurfaceType.Base1Solid)
            || (uint)surface.OrigTextureId == 0)
            return _decodedDimensionsByTexture[key] = (1, 1);

        uint surfaceTextureId = overrideOrigTextureId ?? (uint)surface.OrigTextureId;
        SurfaceTexture? texture = _dats.Get<SurfaceTexture>(surfaceTextureId);
        if (texture is null || texture.Textures.Count == 0)
            return _decodedDimensionsByTexture[key] = (1, 1);

        uint renderSurfaceId = (uint)texture.Textures[0];
        if ((!_dats.Portal.TryGet<RenderSurface>(renderSurfaceId, out RenderSurface? renderSurface)
                && !_dats.HighRes.TryGet<RenderSurface>(renderSurfaceId, out renderSurface))
            || renderSurface.Width <= 0
            || renderSurface.Height <= 0
            || renderSurface.SourceData is null)
            return _decodedDimensionsByTexture[key] = (1, 1);

        return _decodedDimensionsByTexture[key] = (renderSurface.Width, renderSurface.Height);
    }

    /// <summary>
    /// Retail <c>CSurface::Destroy</c> (0x005361F0) releases its current
    /// <c>ImgTex</c>. Mirror that ownership boundary for per-entity composites.
    /// </summary>
    public void ReleaseOwner(uint localEntityId)
    {
        EnsureCompositeTexturesAvailable().ReleaseOwner(localEntityId);
    }

    private void EnsureBindlessAvailable()
    {
        if (_bindless is null)
            throw new InvalidOperationException(
                "TextureCache constructed without BindlessSupport — cannot generate bindless handles. " +
                "WbDrawDispatcher requires the bindless-aware ctor overload (pass non-null BindlessSupport).");
    }

    private CompositeTextureArrayCache EnsureCompositeTexturesAvailable()
    {
        EnsureBindlessAvailable();
        return _compositeTextures!;
    }

    private StandaloneBindlessTextureCache EnsureParticleTexturesAvailable()
    {
        EnsureBindlessAvailable();
        return _particleTextures!;
    }

    private sealed class ParticleTextureBackend(TextureCache owner)
        : IStandaloneBindlessTextureBackend
    {
        public void MakeNonResident(StandaloneBindlessTextureResource resource)
        {
            owner._bindless!.MakeNonResident(resource.Handle);
            Wb.GLHelpers.ThrowOnResourceError(
                owner._gl,
                $"releasing particle texture handle {resource.Handle}");
        }

        public void Delete(StandaloneBindlessTextureResource resource)
            => owner.DeleteUploadedTexture(resource.Name);
    }

    /// <summary>
    /// Advances bounded composite-cache maintenance once per render frame.
    /// Logical owner release is immediate; at most one over-budget layer and
    /// one empty backing array are physically retired in this call.
    /// </summary>
    public void TickCompositeTextureCache() => _compositeTextures?.Tick();

    /// <summary>
    /// Retires at most one over-budget standalone particle texture per render
    /// frame. Keeping this separate from owner release avoids portal-time GPU
    /// destruction bursts without changing live particle range or quality.
    /// </summary>
    public void TickParticleTextureCache() => _particleTextures?.Tick();

    public void BeginCompositeTextureFrame() => _compositeTextures?.BeginFrame();

    /// <summary>
    /// Cheap 64-bit hash over a palette override's identity so two
    /// entities with the same palette setup share a decode. Internal so
    /// the WB dispatcher can compute it once per entity.
    /// </summary>
    internal static ulong HashPaletteOverride(PaletteOverride p)
    {
        // Not cryptographic — just needs to distinguish override setups
        // for caching. Start with base palette id, fold in each entry.
        ulong h = 0xCBF29CE484222325UL;  // FNV-1a offset basis
        const ulong prime = 0x100000001B3UL;
        h = (h ^ p.BasePaletteId) * prime;
        foreach (var sp in p.SubPalettes)
        {
            h = (h ^ sp.SubPaletteId) * prime;
            h = (h ^ sp.Offset) * prime;
            h = (h ^ sp.Length) * prime;
        }
        return h;
    }

    internal static PaletteCompositeIdentity GetPaletteIdentity(PaletteOverride palette) =>
        new(palette, HashPaletteOverride(palette));

    /// <summary>
    /// Phase N.6 slice 1: one-shot surface-format histogram dump for the
    /// atlas-opportunity audit. Activated by ACDREAM_DUMP_SURFACES=1; fires
    /// once after BOTH gates pass:
    /// 1. <c>_dumpFrameCounter &gt;= 600</c> — at least 600 OnRender ticks
    ///    have elapsed (catches the "we're already past startup boilerplate"
    ///    bound; ~10s at 60fps, ~3s at 200fps).
    /// 2. <c>_uploadMetadata.Count &gt;= 100</c> — the cache contains at
    ///    least 100 uploaded textures, indicating streaming has actually
    ///    pulled in world content (not just sky/UI/font). The original
    ///    frame-only gate fired during the login/handshake phase where
    ///    OnRender ticks at GUI rates but no world has streamed in.
    /// Output goes to %LOCALAPPDATA%\acdream\n6-surfaces.txt. Zero cost
    /// when off. See spec §5 in
    /// docs/superpowers/specs/2026-05-11-phase-n6-slice1-design.md.
    /// </summary>
    public void TickSurfaceHistogramDumpIfEnabled()
    {
        if (_surfaceHistogramAlreadyDumped) return;
        if (!string.Equals(System.Environment.GetEnvironmentVariable("ACDREAM_DUMP_SURFACES"), "1", StringComparison.Ordinal)) return;
        _dumpFrameCounter++;
        if (_dumpFrameCounter < 600) return;
        if (_uploadMetadata.Count < 100) return;

        DumpSurfaceHistogram();
        _surfaceHistogramAlreadyDumped = true;
    }

    private void DumpSurfaceHistogram()
    {
        try
        {
            DumpSurfaceHistogramCore();
        }
        catch (Exception ex)
        {
            // Diagnostic-only path. If the dump file can't be written
            // (disk full, permission denied, antivirus lock, path too
            // long) we must NOT crash OnRender — that would invalidate
            // the very measurement pass this diagnostic is meant to
            // support. Log to stderr and let the caller mark the dump
            // as "already done" so it doesn't retry every frame.
            Console.Error.WriteLine($"[N6-DUMP] Failed to write surface histogram: {ex.Message}");
        }
    }

    private void DumpSurfaceHistogramCore()
    {
        var localAppData = System.Environment.GetFolderPath(System.Environment.SpecialFolder.LocalApplicationData);
        var outDir = System.IO.Path.Combine(localAppData, "acdream");
        System.IO.Directory.CreateDirectory(outDir);
        var outPath = System.IO.Path.Combine(outDir, "n6-surfaces.txt");

        var sb = new System.Text.StringBuilder();
        sb.AppendLine($"# acdream surface-format histogram — generated {DateTime.UtcNow:yyyy-MM-ddTHH:mm:ssZ}");
        sb.AppendLine("# Per-entry: surfaceId(hex), width, height, format, byteCount");
        sb.AppendLine();

        // Walk every cached entry across the 6 caches, dedupe by GL name.
        var seen = new HashSet<uint>();
        long totalBytes = 0;
        var bucketsByDim = new Dictionary<(int W, int H), int>();
        var bucketsByFormat = new Dictionary<string, int>();
        var bucketsByTriple = new Dictionary<(int W, int H, string F), int>();

        void Emit(uint surfaceId, uint name)
        {
            if (!seen.Add(name)) return;
            if (!_uploadMetadata.TryGetValue(name, out var meta)) return;
            int bytes = meta.Width * meta.Height * 4;
            totalBytes += bytes;
            sb.AppendLine($"0x{surfaceId:X8}, {meta.Width}, {meta.Height}, {meta.Format}, {bytes}");

            var dimKey = (meta.Width, meta.Height);
            bucketsByDim[dimKey] = bucketsByDim.GetValueOrDefault(dimKey) + 1;
            bucketsByFormat[meta.Format] = bucketsByFormat.GetValueOrDefault(meta.Format) + 1;
            var tripleKey = (meta.Width, meta.Height, meta.Format);
            bucketsByTriple[tripleKey] = bucketsByTriple.GetValueOrDefault(tripleKey) + 1;
        }

        foreach (var kv in _surfacesById)               Emit(kv.Key, kv.Value.Handle);
        _particleTextures?.VisitEntries(resource => Emit(resource.SurfaceId, resource.Name));
        _compositeTextures?.VisitEntries((surfaceId, width, height) =>
        {
            int bytes = checked(width * height * 4);
            totalBytes += bytes;
            sb.AppendLine($"0x{surfaceId:X8}, {width}, {height}, RGBA8_COMPOSITE_LAYER, {bytes}");
            bucketsByDim[(width, height)] = bucketsByDim.GetValueOrDefault((width, height)) + 1;
            bucketsByFormat["RGBA8_COMPOSITE_LAYER"] =
                bucketsByFormat.GetValueOrDefault("RGBA8_COMPOSITE_LAYER") + 1;
            bucketsByTriple[(width, height, "RGBA8_COMPOSITE_LAYER")] =
                bucketsByTriple.GetValueOrDefault((width, height, "RGBA8_COMPOSITE_LAYER")) + 1;
        });

        sb.AppendLine();
        sb.AppendLine("# Rollups");
        sb.AppendLine($"# Total unique GL textures: {seen.Count}");
        sb.AppendLine($"# Total bytes (sum of W*H*4): {totalBytes}");

        sb.AppendLine("# Top 10 (W,H) dimension buckets:");
        foreach (var kv in bucketsByDim.OrderByDescending(kv => kv.Value).Take(10))
            sb.AppendLine($"#   {kv.Key.W}x{kv.Key.H}: {kv.Value}");

        sb.AppendLine("# Format buckets:");
        foreach (var kv in bucketsByFormat.OrderByDescending(kv => kv.Value))
            sb.AppendLine($"#   {kv.Key}: {kv.Value}");

        sb.AppendLine("# Top 10 (W,H,format) triples — atlas-opportunity input:");
        foreach (var kv in bucketsByTriple.OrderByDescending(kv => kv.Value).Take(10))
            sb.AppendLine($"#   {kv.Key.W}x{kv.Key.H} {kv.Key.F}: {kv.Value}");

        System.IO.File.WriteAllText(outPath, sb.ToString());
        Console.WriteLine($"[N6-DUMP] Surface histogram written to {outPath} ({seen.Count} textures, {totalBytes} bytes)");
    }

    private DecodedTexture DecodeFromDats(uint surfaceId, uint? origTextureOverride, PaletteOverride? paletteOverride)
    {
        var surface = _dats.Get<Surface>(surfaceId);
        if (surface is null)
        {
            // TEMP diagnostic (dat-race investigation 2026-06-09, strip with fix)
            Console.WriteLine($"[tex-miss] Surface 0x{surfaceId:X8} -> magenta (thread={System.Environment.CurrentManagedThreadId})");
            return DecodedTexture.Magenta;
        }

        // Base1Solid surfaces (and any with OrigTextureId==0) carry a ColorValue
        // instead of a texture chain. Overrides are irrelevant here — there's
        // no texture chain to swap — so the override is ignored for solid-color
        // surfaces. Translucency is honored so Base1Solid|Translucent surfaces
        // with Translucency=1.0 become alpha=0, which the mesh shader's discard
        // cutout makes invisible.
        if (surface.Type.HasFlag(SurfaceType.Base1Solid) || (uint)surface.OrigTextureId == 0)
            return SurfaceDecoder.DecodeSolidColor(surface.ColorValue, surface.Translucency);

        // Use the override SurfaceTexture id when present, otherwise the
        // Surface's native OrigTextureId.
        uint surfaceTextureId = origTextureOverride ?? (uint)surface.OrigTextureId;
        var surfaceTexture = _dats.Get<SurfaceTexture>(surfaceTextureId);
        if (surfaceTexture is null || surfaceTexture.Textures.Count == 0)
        {
            // TEMP diagnostic (dat-race investigation 2026-06-09, strip with fix)
            Console.WriteLine($"[tex-miss] SurfaceTexture 0x{surfaceTextureId:X8} (surface 0x{surfaceId:X8}) -> magenta (thread={System.Environment.CurrentManagedThreadId})");
            return DecodedTexture.Magenta;
        }

        uint renderSurfaceId = (uint)surfaceTexture.Textures[0];
        if (!_dats.Portal.TryGet<RenderSurface>(renderSurfaceId, out var rs)
            && !_dats.HighRes.TryGet<RenderSurface>(renderSurfaceId, out rs))
        {
            // TEMP diagnostic (dat-race investigation 2026-06-09, strip with fix)
            Console.WriteLine($"[tex-miss] RenderSurface 0x{renderSurfaceId:X8} (surface 0x{surfaceId:X8}) -> magenta (thread={System.Environment.CurrentManagedThreadId})");
            return DecodedTexture.Magenta;
        }

        // Start with the texture's default palette, then apply overlays.
        // ACViewer's Render/TextureCache.IndexToColor does the same and never
        // consults ObjDesc.BasePaletteId for palette-indexed textures — the
        // RenderSurface's own default palette is the starting point.
        Palette? basePalette = rs.DefaultPaletteId != 0
            ? _dats.Get<Palette>(rs.DefaultPaletteId)
            : null;

        Palette? effectivePalette = basePalette;
        if (paletteOverride is not null && basePalette is not null && paletteOverride.SubPalettes.Count > 0)
        {
            effectivePalette = ComposePalette(basePalette, paletteOverride);
        }

        // Clipmap surfaces use palette indices 0..7 as transparent sentinels.
        bool isClipMap = surface.Type.HasFlag(SurfaceType.Base1ClipMap);
        bool isAdditive = surface.Type.HasFlag(SurfaceType.Additive);

        return SurfaceDecoder.DecodeRenderSurface(rs, effectivePalette, isClipMap, isAdditive);
    }

    /// <summary>
    /// Build a composite palette by copying subpalette ranges into a
    /// mutable copy of the base. Ported from ACViewer's
    /// Render/TextureCache.IndexToColor, with network-side Offset/Length
    /// multiplied by 8 to recover the raw palette-index units (ACE's
    /// writer divides by 8 before writing).
    /// </summary>
    private Palette ComposePalette(Palette basePalette, PaletteOverride paletteOverride)
    {
        var composed = new Palette();
        composed.Colors.AddRange(basePalette.Colors);

        foreach (var sp in paletteOverride.SubPalettes)
        {
            var subPal = _dats.Get<Palette>(sp.SubPaletteId);
            if (subPal is null) continue;

            int startIdx = sp.Offset * 8;
            // Length == 0 is the sentinel for "entire palette" per
            // Chorizite.ACProtocol.Types.Subpalette docs. Use a value
            // large enough to cover any real palette; we clamp below.
            int count = sp.Length == 0 ? 2048 : sp.Length * 8;

            for (int j = 0; j < count; j++)
            {
                int idx = startIdx + j;
                if (idx >= composed.Colors.Count || idx >= subPal.Colors.Count)
                    break;
                composed.Colors[idx] = subPal.Colors[idx];
            }
        }

        return composed;
    }

    /// <summary>Uploads a raw RGBA8 byte array as a Texture2D. Used by
    /// <see cref="AcDream.App.UI.IconComposer"/> to upload CPU-composited icon layers.
    /// The returned handle is tracked in <see cref="_adhocHandles"/> and deleted by
    /// <see cref="Dispose"/>. Callers must NOT also store the handle in any of the
    /// keyed caches — that would cause a double-delete on Dispose.</summary>
    public uint UploadRgba8(byte[] rgba, int width, int height, bool nearest = false)
    {
        uint h = UploadRgba8(new DecodedTexture(rgba, width, height), nearest);
        _adhocHandles.Add(h);
        return h;
    }

    private uint UploadRgba8(DecodedTexture decoded, bool nearest = false)
    {
        uint tex = _gl.GenTexture();
        if (tex == 0)
            throw new InvalidOperationException("OpenGL did not create a 2D texture.");
        try
        {
            _gl.BindTexture(TextureTarget.Texture2D, tex);

            fixed (byte* p = decoded.Rgba8)
                _gl.TexImage2D(
                    TextureTarget.Texture2D,
                    0,
                    InternalFormat.Rgba8,
                    (uint)decoded.Width,
                    (uint)decoded.Height,
                    0,
                    PixelFormat.Rgba,
                    PixelType.UnsignedByte,
                    p);

            // Point (nearest) sampling for pixel-exact UI text — bilinear softens the dat
            // font's small glyphs. Other surfaces use bilinear.
            int filter = nearest ? (int)TextureMinFilter.Nearest : (int)TextureMinFilter.Linear;
            _gl.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, filter);
            _gl.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, filter);
            _gl.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapS, (int)TextureWrapMode.Repeat);
            _gl.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapT, (int)TextureWrapMode.Repeat);
            Wb.GLHelpers.ThrowOnResourceError(
                _gl,
                $"uploading 2D RGBA8 texture {decoded.Width}x{decoded.Height}");

            TrackUploadedTexture(tex, decoded.Width, decoded.Height);
            return tex;
        }
        catch
        {
            _gl.DeleteTexture(tex);
            throw;
        }
        finally
        {
            _gl.BindTexture(TextureTarget.Texture2D, 0);
        }
    }

    /// <summary>
    /// Variant of <see cref="UploadRgba8"/> that uploads pixel data as a 1-layer
    /// Texture2DArray. Required by the WB modern rendering path which samples via
    /// sampler2DArray in its bindless shader. Pixel data is identical.
    /// </summary>
    private uint UploadRgba8AsLayer1Array(DecodedTexture decoded)
    {
        uint tex = _gl.GenTexture();
        if (tex == 0)
            throw new InvalidOperationException("OpenGL did not create a one-layer texture array.");
        try
        {
            _gl.BindTexture(TextureTarget.Texture2DArray, tex);

            fixed (byte* p = decoded.Rgba8)
                _gl.TexImage3D(
                    TextureTarget.Texture2DArray,
                    0,
                    InternalFormat.Rgba8,
                    (uint)decoded.Width,
                    (uint)decoded.Height,
                    depth: 1,
                    border: 0,
                    PixelFormat.Rgba,
                    PixelType.UnsignedByte,
                    p);

            _gl.TexParameter(TextureTarget.Texture2DArray, TextureParameterName.TextureMinFilter, (int)TextureMinFilter.Linear);
            _gl.TexParameter(TextureTarget.Texture2DArray, TextureParameterName.TextureMagFilter, (int)TextureMagFilter.Linear);
            _gl.TexParameter(TextureTarget.Texture2DArray, TextureParameterName.TextureWrapS,     (int)TextureWrapMode.Repeat);
            _gl.TexParameter(TextureTarget.Texture2DArray, TextureParameterName.TextureWrapT,     (int)TextureWrapMode.Repeat);
            Wb.GLHelpers.ThrowOnResourceError(
                _gl,
                $"uploading one-layer RGBA8 array {decoded.Width}x{decoded.Height}");

            TrackUploadedTexture(tex, decoded.Width, decoded.Height);
            return tex;
        }
        catch
        {
            _gl.DeleteTexture(tex);
            throw;
        }
        finally
        {
            _gl.BindTexture(TextureTarget.Texture2DArray, 0);
        }
    }

    private void TrackUploadedTexture(uint name, int width, int height)
    {
        _uploadMetadata[name] = (width, height, "RGBA8_DECODED");
        long bytes = checked((long)width * height * 4L);
        Wb.GpuMemoryTracker.TrackResourceAllocation(Wb.GpuResourceType.Texture);
        Wb.GpuMemoryTracker.TrackAllocation(bytes, Wb.GpuResourceType.Texture);
    }

    private void DeleteUploadedTexture(uint name)
    {
        _gl.DeleteTexture(name);
        Wb.GLHelpers.ThrowOnResourceError(_gl, $"deleting uploaded texture {name}");

        if (_uploadMetadata.Remove(name, out var metadata))
        {
            long bytes = checked((long)metadata.Width * metadata.Height * 4L);
            Wb.GpuMemoryTracker.TrackDeallocation(bytes, Wb.GpuResourceType.Texture);
            Wb.GpuMemoryTracker.TrackResourceDeallocation(Wb.GpuResourceType.Texture);
        }
    }

    public void Dispose()
    {
        // GameWindow drains frame-flight fences before this teardown. The
        // bindless caches make every handle non-resident before deleting
        // their backing storage.
        _particleTextures?.Dispose();
        _compositeTextures?.Dispose();

        _paletteIndexedByTexture.Clear();

        // Legacy Texture2D textures.
        foreach (var entry in _surfacesById.Values)
            DeleteUploadedTexture(entry.Handle);
        _surfacesById.Clear();

        if (_magentaHandle != 0)
        {
            DeleteUploadedTexture(_magentaHandle);
            _magentaHandle = 0;
        }

        // RenderSurface (UI sprite) handles — pre-existing gap: this dict was populated
        // by GetOrUploadRenderSurface but was not swept here before this fix.
        foreach (var h in _handlesByRenderSurfaceId.Values)
            DeleteUploadedTexture(h);
        _handlesByRenderSurfaceId.Clear();

        // Ad-hoc handles from the public UploadRgba8(byte[],int,int,bool) wrapper
        // (IconComposer composited icons). Not stored in any keyed cache.
        foreach (var h in _adhocHandles)
            DeleteUploadedTexture(h);
        _adhocHandles.Clear();
    }
}