using System.IO;

using System.Linq;

using System.Text;

namespace BCnEncoder.Shared.ImageFiles

{

/// <summary>

/// The format identifier of an image file.

/// </summary>

public enum ImageFileFormat

{

/// <summary>

/// Represents the KTX image file format.

/// </summary>

Ktx,

/// <summary>

/// Represents the DDS image file format.

/// </summary>

Dds,

/// <summary>

/// Represents an unknown image file format.

/// </summary>

Unknown

}

/// <summary>

/// Static helper class to determine the format of an image file.

/// </summary>

public static class ImageFile

{

private static readonly byte[] ktx1Identifier = { 0xAB, 0x4B, 0x54, 0x58, 0x20, 0x31, 0x31, 0xBB, 0x0D, 0x0A, 0x1A, 0x0A };

/// <summary>

/// Determines the image file format of the given stream.

/// </summary>

/// <param name="stream">The stream of data to identify.</param>

/// <returns>The format this image file may contain.</returns>

public static ImageFileFormat DetermineImageFormat(Stream stream)

{

if (IsDds(stream))

{

return ImageFileFormat.Dds;

}

if (IsKtx(stream))

{

return ImageFileFormat.Ktx;

}

return ImageFileFormat.Unknown;

}

private static bool IsDds(Stream stream)

{

using var br = new BinaryReader(stream, Encoding.UTF8, true);

var magic = br.ReadUInt32();

stream.Position -= 4;

return magic == 0x20534444U;

}

private static bool IsKtx(Stream stream)

{

// Only checks for version 1

using var br = new BinaryReader(stream, Encoding.ASCII, true);

var identifier = br.ReadBytes(12);

stream.Position -= 12;

return identifier.SequenceEqual(ktx1Identifier);

}

}

}