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

namespace AcDream.App.Rendering;

public sealed unsafe class TextureCache : Wb.ITextureCachePerInstance, IDisposable
{
    private readonly GL _gl;
    private readonly DatCollection _dats;
    private readonly Dictionary<uint, uint> _handlesBySurfaceId = new();
    /// <summary>
    /// Composite cache for surface-with-override-origtex entries (Phase 5
    /// TextureChanges). Key = (baseSurfaceId, overrideOrigTextureId),
    /// value = GL texture handle.
    /// </summary>
    private readonly Dictionary<(uint surfaceId, uint origTexOverride), uint> _handlesByOverridden = new();
    /// <summary>
    /// Composite cache for palette-overridden entries (Phase 5 SubPalettes).
    /// Key = (baseSurfaceId, origTexOverride, paletteHash), value = handle.
    /// paletteHash is a cheap combined hash of the PaletteOverride's ids +
    /// offsets + lengths so two entities with equivalent palette setups
    /// share the same decoded texture.
    /// </summary>
    private readonly Dictionary<(uint surfaceId, uint origTexOverride, ulong paletteHash), uint> _handlesByPalette = new();
    private uint _magentaHandle;

    public TextureCache(GL gl, DatCollection dats)
    {
        _gl = gl;
        _dats = dats;
    }

    /// <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)
    {
        if (_handlesBySurfaceId.TryGetValue(surfaceId, out var h))
            return h;

        var decoded = DecodeFromDats(surfaceId, origTextureOverride: null, paletteOverride: null);
        if (System.Environment.GetEnvironmentVariable("ACDREAM_DUMP_SKY") == "1")
            DumpAlphaHistogram(surfaceId, decoded);
        h = UploadRgba8(decoded);
        _handlesBySurfaceId[surfaceId] = h;
        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>
    /// Get or upload a texture for a Surface id but with its
    /// <c>OrigTextureId</c> replaced by <paramref name="overrideOrigTextureId"/>.
    /// The Surface's other properties (type flags, color, translucency,
    /// clipmap handling, default palette) are preserved — only the
    /// SurfaceTexture lookup is swapped. This is how the server's
    /// CreateObject.TextureChanges are applied at render time.
    /// Caches under a composite key so multiple entities can share.
    /// </summary>
    public uint GetOrUploadWithOrigTextureOverride(uint surfaceId, uint overrideOrigTextureId)
    {
        var key = (surfaceId, overrideOrigTextureId);
        if (_handlesByOverridden.TryGetValue(key, out var h))
            return h;

        var decoded = DecodeFromDats(surfaceId, origTextureOverride: overrideOrigTextureId, paletteOverride: null);
        h = UploadRgba8(decoded);
        _handlesByOverridden[key] = h;
        return h;
    }

    /// <summary>
    /// Full Phase 5 override: for palette-indexed textures (PFID_P8 /
    /// PFID_INDEX16), applies <paramref name="paletteOverride"/>'s
    /// subpalette overlays on top of the texture's default palette
    /// before decoding. Non-palette formats ignore the palette override.
    /// Also honors <paramref name="overrideOrigTextureId"/> if non-null.
    /// </summary>
    public uint GetOrUploadWithPaletteOverride(
        uint surfaceId,
        uint? overrideOrigTextureId,
        PaletteOverride paletteOverride)
        => GetOrUploadWithPaletteOverride(surfaceId, overrideOrigTextureId, paletteOverride,
            HashPaletteOverride(paletteOverride));

    /// <summary>
    /// Overload that accepts a precomputed palette hash. Lets callers (e.g.
    /// the WB draw dispatcher) compute the hash ONCE per entity and reuse
    /// it across every (part, batch) lookup, avoiding the per-batch
    /// FNV-1a fold over <see cref="PaletteOverride.SubPalettes"/>.
    /// </summary>
    public uint GetOrUploadWithPaletteOverride(
        uint surfaceId,
        uint? overrideOrigTextureId,
        PaletteOverride paletteOverride,
        ulong precomputedPaletteHash)
    {
        uint origTexKey = overrideOrigTextureId ?? 0;
        var key = (surfaceId, origTexKey, precomputedPaletteHash);
        if (_handlesByPalette.TryGetValue(key, out var h))
            return h;

        var decoded = DecodeFromDats(surfaceId, origTextureOverride: overrideOrigTextureId, paletteOverride: paletteOverride);
        h = UploadRgba8(decoded);
        _handlesByPalette[key] = h;
        return h;
    }

    /// <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;
    }

    private DecodedTexture DecodeFromDats(uint surfaceId, uint? origTextureOverride, PaletteOverride? paletteOverride)
    {
        var surface = _dats.Get<Surface>(surfaceId);
        if (surface is null)
            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)
            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))
            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;
    }

    private uint UploadRgba8(DecodedTexture decoded)
    {
        uint tex = _gl.GenTexture();
        _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);

        _gl.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMinFilter, (int)TextureMinFilter.Linear);
        _gl.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureMagFilter, (int)TextureMagFilter.Linear);
        _gl.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapS, (int)TextureWrapMode.Repeat);
        _gl.TexParameter(TextureTarget.Texture2D, TextureParameterName.TextureWrapT, (int)TextureWrapMode.Repeat);

        _gl.BindTexture(TextureTarget.Texture2D, 0);
        return tex;
    }

    public void Dispose()
    {
        foreach (var h in _handlesBySurfaceId.Values)
            _gl.DeleteTexture(h);
        _handlesBySurfaceId.Clear();
        foreach (var h in _handlesByOverridden.Values)
            _gl.DeleteTexture(h);
        _handlesByOverridden.Clear();
        foreach (var h in _handlesByPalette.Values)
            _gl.DeleteTexture(h);
        _handlesByPalette.Clear();
        if (_magentaHandle != 0)
        {
            _gl.DeleteTexture(_magentaHandle);
            _magentaHandle = 0;
        }
    }
}