using System.Buffers.Binary;
using ErsatzTV.Infrastructure.Images;
using NUnit.Framework;
using Shouldly;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.Formats;
using SixLabors.ImageSharp.Formats.Bmp;
using SixLabors.ImageSharp.Formats.Jpeg;
using SixLabors.ImageSharp.Formats.Png;
using SixLabors.ImageSharp.Formats.Tiff;
using SixLabors.ImageSharp.Formats.Webp;
using SixLabors.ImageSharp.Metadata.Profiles.Icc;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using Image = SixLabors.ImageSharp.Image;

namespace ErsatzTV.Infrastructure.Tests.Images;

/// <summary>
///     ImageSharp 3.1.12's TIFF decoder carries GHSA-v76p-62qx-wwq2 and GHSA-wmxv-xphr-5c9g, and the
///     patched releases need a Six Labors license key to build in Release, so every ImageSharp decode
///     goes through a configuration that cannot detect TIFF. (ersatztv#929,
///     security.imagesharp-3x-tiff-decoder-disabled)
/// </summary>
[TestFixture]
public class ImageSharpDecodingTests
{
    private static readonly Uri Uri = new("https://example.com/logo.tif");

    // the list is derived from Configuration.Default, not restated: a package bump that adds or
    // drops a format reddens this instead of silently changing what ErsatzTV can decode
    [Test]
    public void Configuration_Registers_Every_Default_Format_Except_Tiff()
    {
        var expected = Configuration.Default.ImageFormats
            .Where(f => f is not TiffFormat)
            .Select(f => f.Name)
            .OrderBy(n => n, StringComparer.Ordinal)
            .ToList();

        var actual = ImageSharpDecoding.Configuration.ImageFormats
            .Select(f => f.Name)
            .OrderBy(n => n, StringComparer.Ordinal)
            .ToList();

        actual.ShouldBe(expected);
    }

    // the exclusion above is only meaningful while Default really does carry TIFF, and building
    // the restricted configuration must not have removed it from the process-wide Default
    [Test]
    public void Configuration_Default_Still_Registers_Tiff()
    {
        _ = ImageSharpDecoding.Configuration;
        Configuration.Default.ImageFormats.ShouldContain(f => f is TiffFormat);
    }

    // positive control for the rejections below: the fixture is a TIFF ImageSharp can decode,
    // so a rejection is the configuration's doing and not a broken fixture
    [Test]
    public async Task Tiff_Fixture_Decodes_Under_The_Default_Configuration()
    {
        await using MemoryStream stream = await RealTiff(64, 32);
        using Image image = await Image.LoadAsync(stream);
        image.Width.ShouldBe(64);
        image.Height.ShouldBe(32);
    }

    // the validator as a whole (render path, save path and upload path). The Identify pass rejects
    // a TIFF before the Load pass runs, so this exercises Identify; that the Load pass takes the
    // same options is held by ErsatzTV.Architecture.Tests' ImageSharpSurfaceTests.
    [Test]
    public async Task DecodeAndValidate_Rejects_A_Tiff_As_An_Unknown_Format()
    {
        await using MemoryStream stream = await RealTiff(64, 32);
        await Should.ThrowAsync<UnknownImageFormatException>(
            () => RemoteImageValidator.DecodeAndValidate(stream, Uri, CancellationToken.None));
    }

    // pins the IDENTIFY pass separately. The header declares 30000x30000: an Identify that could
    // read TIFF would report those dimensions and the budget check would throw
    // InvalidOperationException("pixel limit") instead, so only a TIFF-blind Identify yields
    // UnknownImageFormatException here. The IFD walk Identify performs is where the BigTIFF
    // non-progressing loop (GHSA-wmxv-xphr-5c9g) lives, so the header pass must not reach it.
    [Test]
    public async Task DecodeAndValidate_Rejects_A_Tiff_Before_Reading_Its_Header()
    {
        await using MemoryStream stream = await TiffDeclaring(30000, 30000);

        ImageInfo info = await Image.IdentifyAsync(stream);
        info.Width.ShouldBe(30000);
        stream.Position = 0;

        await Should.ThrowAsync<UnknownImageFormatException>(
            () => RemoteImageValidator.DecodeAndValidate(stream, Uri, CancellationToken.None));
    }

    // --- GHSA-gwg2-r3hj-4w44: the ICC CLUT parser allocates from unvalidated grid dimensions ---
    //
    // ErsatzTV never reads ICC entries (ImageSharpSurfaceTests bans the namespace), but decode,
    // CloneFrame, Resize and CloneAs all carry the profile along. Whether any of them parses it is
    // ImageSharp's own runtime behaviour, which an IL scan of ErsatzTV cannot see, so it is pinned
    // here by allocation. A version that parses the profile on decode or clone reddens these
    // instead of reopening the advisory silently.

    private const long HostileIccEntriesFloor = 64L * 1024 * 1024;
    internal const long ProductPathCeiling = 16L * 1024 * 1024;

    internal static readonly string[] IccCarriers = ["bmp", "jpeg", "png", "webp"];

    // the carrier list is checked, not trusted: every format the decode configuration registers is
    // round-tripped with the hostile profile through its default encoder, and the formats whose
    // decode still carries a profile must be exactly IccCarriers. A version that adds ICC support to
    // another format reddens here. A round trip cannot see a decoder that reads a profile its own
    // encoder never writes; on 3.1.12 the decoders that construct an IccProfile are BMP, JPEG, PNG,
    // WebP and TIFF (Cecil scan of the package, 2026-10-28), so none is missed today.
    [Test]
    public async Task Icc_Carriers_Are_Every_Configured_Format_That_Round_Trips_A_Profile()
    {
        var carriers = new List<string>();
        foreach (IImageFormat format in ImageSharpDecoding.Configuration.ImageFormats)
        {
            IImageEncoder encoder = Configuration.Default.ImageFormatsManager.GetEncoder(format);
            await using MemoryStream stream = await WithHostileIcc(encoder);
            using Image image = await Image.LoadAsync(ImageSharpDecoding.Options(), stream);
            if (image.Metadata.IccProfile is not null)
            {
                carriers.Add(format.Name.ToLowerInvariant());
            }
        }

        carriers.Order(StringComparer.Ordinal).ShouldBe(IccCarriers.Order(StringComparer.Ordinal));
    }

    // positive control: the fixture really is hostile. Reading Entries runs the CLUT reader on the
    // declared 255-point, 3-input grid (about 127 MiB on 3.1.12, measured 2026-10-28); the catch
    // only tolerates the truncated table throwing afterwards.
    [TestCaseSource(nameof(IccCarriers))]
    [NonParallelizable]
    public async Task Hostile_Icc_Fixture_Allocates_When_Its_Entries_Are_Parsed(string format)
    {
        await using MemoryStream stream = await WithHostileIcc(format);
        using Image image = await Image.LoadAsync(ImageSharpDecoding.Options(), stream);
        IccProfile profile = image.Metadata.IccProfile.ShouldNotBeNull();

        long allocated = AllocatedDuring(() =>
        {
            try
            {
                _ = profile.Entries;
            }
            catch (Exception)
            {
                // the allocation is what is measured, not whether the truncated table throws
            }
        });

        TestContext.Out.WriteLine($"{format}: reading Entries allocated {allocated / 1024} KiB");
        allocated.ShouldBeGreaterThan(HostileIccEntriesFloor);
    }

    // the product path: the validator's two decodes, then the per-frame CloneFrame + Resize +
    // CloneAs that ImageElementBase runs. The profile must survive the path (so the bound is not
    // vacuous because a decoder dropped it) and nothing on it may size the CLUT.
    [TestCaseSource(nameof(IccCarriers))]
    [NonParallelizable]
    public async Task Decode_Clone_And_Resize_Do_Not_Parse_A_Hostile_Icc_Profile(string format)
    {
        await using MemoryStream stream = await WithHostileIcc(format);

        long allocated = await AllocatedDuringAsync(async () =>
        {
            using Image image = await RemoteImageValidator.DecodeAndValidate(stream, Uri, CancellationToken.None);
            image.Metadata.IccProfile.ShouldNotBeNull();

            using Image frame = image.Frames.CloneFrame(0);
            frame.Mutate(ctx => ctx.Resize(8, 8));
            frame.Metadata.IccProfile.ShouldNotBeNull();

            using Image<Rgba32> rgba = frame.CloneAs<Rgba32>();
            rgba.Metadata.IccProfile.ShouldNotBeNull();
        });

        TestContext.Out.WriteLine($"{format}: decode, clone and resize allocated {allocated / 1024} KiB");
        allocated.ShouldBeLessThan(ProductPathCeiling);
    }

    /// <summary>
    ///     A 16x16 image in <paramref name="format" /> carrying an ICC profile whose A2B0 tag is an
    ///     <c>mft2</c> (lut16) with 3 inputs, 15 outputs and 255 grid points, truncated before the
    ///     CLUT: a 208-byte profile.
    /// </summary>
    internal static Task<MemoryStream> WithHostileIcc(string format) =>
        WithHostileIcc(
            format switch
            {
                "bmp" => new BmpEncoder(),
                "jpeg" => new JpegEncoder(),
                "png" => new PngEncoder(),
                "webp" => new WebpEncoder { FileFormat = WebpFileFormatType.Lossless },
                _ => throw new ArgumentOutOfRangeException(nameof(format), format, null)
            });

    private static async Task<MemoryStream> WithHostileIcc(IImageEncoder encoder)
    {
        using var image = new Image<Rgba32>(16, 16);
        image.Metadata.IccProfile = new IccProfile(HostileIccBytes());

        var stream = new MemoryStream();
        await image.SaveAsync(stream, encoder);
        stream.Position = 0;
        return stream;
    }

    private static byte[] HostileIccBytes()
    {
        // mft2: type, reserved, in/out/grid/pad, 3x3 matrix, input/output table entry counts,
        // then the three 2-entry input tables, and no CLUT
        var tag = new List<byte>();
        tag.AddRange("mft2"u8.ToArray());
        tag.AddRange(new byte[4]);
        tag.AddRange([3, 15, 255, 0]);
        for (var i = 0; i < 9; i++)
        {
            tag.AddRange(BigEndian(i % 4 == 0 ? 0x00010000u : 0u));
        }

        tag.AddRange([0, 2, 0, 2]);
        tag.AddRange(new byte[3 * 2 * 2]);

        const int TagOffset = 128 + 4 + 12;
        int size = TagOffset + tag.Count;

        var bytes = new byte[size];
        BinaryPrimitives.WriteUInt32BigEndian(bytes.AsSpan(0), (uint)size);
        BinaryPrimitives.WriteUInt32BigEndian(bytes.AsSpan(8), 0x02100000u);
        "mntr"u8.CopyTo(bytes.AsSpan(12));
        "RGB "u8.CopyTo(bytes.AsSpan(16));
        "XYZ "u8.CopyTo(bytes.AsSpan(20));
        "acsp"u8.CopyTo(bytes.AsSpan(36));
        BinaryPrimitives.WriteUInt32BigEndian(bytes.AsSpan(128), 1);
        "A2B0"u8.CopyTo(bytes.AsSpan(132));
        BinaryPrimitives.WriteUInt32BigEndian(bytes.AsSpan(136), TagOffset);
        BinaryPrimitives.WriteUInt32BigEndian(bytes.AsSpan(140), (uint)tag.Count);
        tag.CopyTo(bytes, TagOffset);
        return bytes;
    }

    private static byte[] BigEndian(uint value)
    {
        var bytes = new byte[4];
        BinaryPrimitives.WriteUInt32BigEndian(bytes, value);
        return bytes;
    }

    // process-wide and precise, because the async path may resume on another thread; the callers
    // are [NonParallelizable] so no other test's allocations land in the count
    private static long AllocatedDuring(Action action)
    {
        long before = GC.GetTotalAllocatedBytes(precise: true);
        action();
        return GC.GetTotalAllocatedBytes(precise: true) - before;
    }

    private static async Task<long> AllocatedDuringAsync(Func<Task> action)
    {
        long before = GC.GetTotalAllocatedBytes(precise: true);
        await action();
        return GC.GetTotalAllocatedBytes(precise: true) - before;
    }

    internal static async Task<MemoryStream> RealTiff(int width, int height)
    {
        using var image = new Image<Rgba32>(width, height);
        var stream = new MemoryStream();
        await image.SaveAsync(stream, new TiffEncoder());
        stream.Position = 0;
        return stream;
    }

    /// <summary>
    ///     A real TIFF whose ImageWidth/ImageLength IFD entries are rewritten to declare
    ///     <paramref name="width" /> x <paramref name="height" />, so Identify reports a size the
    ///     pixel data does not back.
    /// </summary>
    private static async Task<MemoryStream> TiffDeclaring(int width, int height)
    {
        await using MemoryStream source = await RealTiff(8, 8);
        byte[] bytes = source.ToArray();

        // TiffEncoder writes little-endian ("II"); the first IFD offset is at byte 4
        bytes[0].ShouldBe((byte)'I');
        var ifd = (int)BinaryPrimitives.ReadUInt32LittleEndian(bytes.AsSpan(4));
        int count = BinaryPrimitives.ReadUInt16LittleEndian(bytes.AsSpan(ifd));

        var patched = 0;
        for (var i = 0; i < count; i++)
        {
            int entry = ifd + 2 + i * 12;
            ushort tag = BinaryPrimitives.ReadUInt16LittleEndian(bytes.AsSpan(entry));
            ushort type = BinaryPrimitives.ReadUInt16LittleEndian(bytes.AsSpan(entry + 2));
            if (tag is not (256 or 257))
            {
                continue;
            }

            int value = tag == 256 ? width : height;
            Span<byte> slot = bytes.AsSpan(entry + 8, 4);
            slot.Clear();
            if (type == 3)
            {
                BinaryPrimitives.WriteUInt16LittleEndian(slot, checked((ushort)value));
            }
            else
            {
                BinaryPrimitives.WriteUInt32LittleEndian(slot, (uint)value);
            }

            patched++;
        }

        patched.ShouldBe(2);
        return new MemoryStream(bytes);
    }
}