Wp2ghost/GhostImageManager/Services/ImageDimensionReader.cs

namespace GhostImageManager.Services;

public static class ImageDimensionReader
{
    public static (int Width, int Height) Read(Stream stream)
    {
        using var reader = new BinaryReader(stream);
        var header = reader.ReadBytes(8);

        if (IsJpeg(header))
            return ReadJpeg(stream, reader);

        if (IsPng(header))
            return ReadPng(reader);

        if (IsGif(header))
            return ReadGif(reader);

        if (IsWebP(header))
            return ReadWebP(stream, reader);

        return (0, 0);
    }

    private static bool IsJpeg(byte[] header) => header[0] == 0xFF && header[1] == 0xD8;
    private static bool IsPng(byte[] header) => header[0] == 0x89 && header[1] == 0x50 && header[2] == 0x4E && header[3] == 0x47;
    private static bool IsGif(byte[] header) => header[0] == 0x47 && header[1] == 0x49 && header[2] == 0x46;
    private static bool IsWebP(byte[] header) => header[0] == 0x52 && header[1] == 0x49 && header[2] == 0x46 && header[3] == 0x46;

    private static (int, int) ReadPng(BinaryReader reader)
    {
        reader.BaseStream.Seek(16, SeekOrigin.Begin);
        var width = ReadBigEndianInt(reader);
        var height = ReadBigEndianInt(reader);
        return (width, height);
    }

    private static (int, int) ReadGif(BinaryReader reader)
    {
        reader.BaseStream.Seek(6, SeekOrigin.Begin);
        var width = reader.ReadUInt16();
        var height = reader.ReadUInt16();
        return (width, height);
    }

    private static (int, int) ReadJpeg(Stream stream, BinaryReader reader)
    {
        stream.Seek(2, SeekOrigin.Begin);
        while (stream.Position < stream.Length)
        {
            int marker = reader.ReadByte();
            if (marker != 0xFF) continue;

            int type = reader.ReadByte();
            if (type == 0xD9 || type == 0xDA) break; // EOI or SOS

            // Skip padding
            while (type == 0xFF) type = reader.ReadByte();
            if (type == 0xD9 || type == 0xDA) break;

            if (type == 0xD8 || type == 0x01) continue;

            int length = (reader.ReadByte() << 8) | reader.ReadByte();
            if (length < 2) break;

            if (type == 0xC0 || type == 0xC1 || type == 0xC2 || type == 0xC3 ||
                type == 0xC5 || type == 0xC6 || type == 0xC7 ||
                type == 0xC9 || type == 0xCA || type == 0xCB ||
                type == 0xCD || type == 0xCE || type == 0xCF)
            {
                reader.ReadByte(); // precision
                int height = (reader.ReadByte() << 8) | reader.ReadByte();
                int width = (reader.ReadByte() << 8) | reader.ReadByte();
                return (width, height);
            }

            stream.Seek(length - 2, SeekOrigin.Current);
        }

        return (0, 0);
    }

    private static (int, int) ReadWebP(Stream stream, BinaryReader reader)
    {
        stream.Seek(12, SeekOrigin.Begin); // Skip RIFF....WEBP
        var chunk = reader.ReadChars(4);
        var chunkType = new string(chunk);

        if (chunkType == "VP8 ")
        {
            stream.Seek(26, SeekOrigin.Begin);
            int width = reader.ReadUInt16() & 0x3FFF;
            int height = reader.ReadUInt16() & 0x3FFF;
            return (width, height);
        }

        if (chunkType == "VP8L")
        {
            stream.Seek(21, SeekOrigin.Begin);
            int data = reader.ReadInt32();
            int width = (data & 0x3FFF) + 1;
            int height = ((data >> 14) & 0x3FFF) + 1;
            return (width, height);
        }

        if (chunkType == "VP8X")
        {
            stream.Seek(24, SeekOrigin.Begin);
            var sizeBytes = reader.ReadBytes(6);
            int width = (sizeBytes[0] | (sizeBytes[1] << 8) | (sizeBytes[2] << 16)) + 1;
            int height = (sizeBytes[3] | (sizeBytes[4] << 8) | (sizeBytes[5] << 16)) + 1;
            return (width, height);
        }

        return (0, 0);
    }

    private static int ReadBigEndianInt(BinaryReader reader)
    {
        var bytes = reader.ReadBytes(4);
        return (bytes[0] << 24) | (bytes[1] << 16) | (bytes[2] << 8) | bytes[3];
    }
}