view-by-distance-mklink-console/Metadata/Models/Stateless/Dimensions.cs

using System.Drawing;

namespace View_by_Distance.Metadata.Models.Stateless.Methods;

internal static class Dimensions
{

#pragma warning disable IDE0230
    private static readonly Dictionary<byte[], Func<BinaryReader, Size?>> _ImageFormatDecoders = new()
    {
        { new byte[] { 0xff, 0xd8 }, DecodeJfif },
        { new byte[] { 0x42, 0x4D }, DecodeBitmap },
        { new byte[] { 0x52, 0x49, 0x46, 0x46 }, DecodeWebP },
        { new byte[] { 0x47, 0x49, 0x46, 0x38, 0x37, 0x61 }, DecodeGif },
        { new byte[] { 0x47, 0x49, 0x46, 0x38, 0x39, 0x61 }, DecodeGif },
        { new byte[] { 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A }, DecodePng },
    };
#pragma warning restore IDE0230

    private static bool StartsWith(List<byte> thisBytes, byte[] thatBytes)
    {
        for (int i = 0; i < thisBytes.Count && i < thatBytes.Length; i += 1)
        {
            if (thisBytes[i] == thatBytes[i])
                continue;
            return false;
        }
        return true;
    }

    private static short ReadLittleEndianInt16(BinaryReader binaryReader)
    {
        byte[] bytes = new byte[sizeof(short)];
        for (int i = 0; i < sizeof(short); i += 1)
            bytes[sizeof(short) - 1 - i] = binaryReader.ReadByte();
        return BitConverter.ToInt16(bytes, 0);
    }

    private static int ReadLittleEndianInt32(BinaryReader binaryReader)
    {
        byte[] bytes = new byte[sizeof(int)];
        for (int i = 0; i < sizeof(int); i += 1)
            bytes[sizeof(int) - 1 - i] = binaryReader.ReadByte();
        return BitConverter.ToInt32(bytes, 0);
    }

    private static Size? DecodeBitmap(BinaryReader binaryReader)
    {
        _ = binaryReader.ReadBytes(16);
        int width = binaryReader.ReadInt32();
        int height = binaryReader.ReadInt32();
        return new Size(width, height);
    }

    private static Size? DecodeGif(BinaryReader binaryReader)
    {
        int width = binaryReader.ReadInt16();
        int height = binaryReader.ReadInt16();
        return new Size(width, height);
    }

    private static Size? DecodePng(BinaryReader binaryReader)
    {
        _ = binaryReader.ReadBytes(8);
        int width = ReadLittleEndianInt32(binaryReader);
        int height = ReadLittleEndianInt32(binaryReader);
        return new Size(width, height);
    }

    private static Size? DecodeJfif(BinaryReader binaryReader)
    {
        while (binaryReader.ReadByte() == 0xff)
        {
            byte marker = binaryReader.ReadByte();
            short chunkLength = ReadLittleEndianInt16(binaryReader);
            if (marker == 0xc0)
            {
                _ = binaryReader.ReadByte();
                int height = ReadLittleEndianInt16(binaryReader);
                int width = ReadLittleEndianInt16(binaryReader);
                return new Size(width, height);
            }
            if (chunkLength >= 0)
                _ = binaryReader.ReadBytes(chunkLength - 2);
            else
            {
                ushort uChunkLength = (ushort)chunkLength;
                _ = binaryReader.ReadBytes(uChunkLength - 2);
            }
        }
        return null;
    }

    private static Size? DecodeWebP(BinaryReader binaryReader)
    {
        _ = binaryReader.ReadUInt32(); // Size
        _ = binaryReader.ReadBytes(15); // WEBP, VP8 + more
        _ = binaryReader.ReadBytes(3); // SYNC
        int width = binaryReader.ReadUInt16() & 0b00_11111111111111; // 14 bits width
        int height = binaryReader.ReadUInt16() & 0b00_11111111111111; // 14 bits height
        return new Size(width, height);
    }

    internal static Size? GetDimensions(BinaryReader binaryReader)
    {
        Size? result;
        List<byte> magicBytes = [];
        int[] magicBytesLengths = (from l in _ImageFormatDecoders.Keys where l.Length <= binaryReader.BaseStream.Length orderby l.Length descending select l.Length).ToArray();
        if (magicBytesLengths.Length == 0)
            result = null;
        else
        {
            result = null;
            if (binaryReader.BaseStream.Length == binaryReader.BaseStream.Position)
                _ = binaryReader.BaseStream.Seek(0, SeekOrigin.Begin);
            for (int i = 0; i < magicBytesLengths[0]; i++)
            {
                magicBytes.Add(binaryReader.ReadByte());
                foreach (KeyValuePair<byte[], Func<BinaryReader, Size?>> kvPair in _ImageFormatDecoders)
                {
                    if (StartsWith(magicBytes, kvPair.Key))
                    {
                        result = kvPair.Value(binaryReader);
                        break;
                    }
                }
                if (result is not null)
                    break;
            }
        }
        return result;
    }

    internal static Size? GetDimensions(string path)
    {
        Size? result;
        using FileStream fileStream = File.OpenRead(path);
        using BinaryReader binaryReader = new(fileStream);
        result = GetDimensions(binaryReader);
        return result;
    }

}