// Copyright (c) 2023 bradson
// This Source Code Form is subject to the terms of the Mozilla Public
// License, v. 2.0. If a copy of the MPL was not distributed with this
// file, You can obtain one at https://mozilla.org/MPL/2.0/.

using System.IO;

namespace PerformanceFish;

//DDS importing from // https://github.com/sarbian/DDSLoader/blob/master/DatabaseLoaderTexture_DDS.cs
public static class DDSLoader
{
	private const uint
		DDSD_MIPMAPCOUNT_BIT = 0x00020000,
		DDPF_ALPHAPIXELS = 0x00000001,
		DDPF_ALPHA = 0x00000002,
		DDPF_FOURCC = 0x00000004,
		DDPF_RGB = 0x00000040,
		// DDPF_YUV = 0x00000200,
		DDPF_LUMINANCE = 0x00020000;
		// DDPF_NORMAL = 0x80000000;

	public static string? error;

	// DDS Texture loader inspired by
	// http://answers.unity3d.com/questions/555984/can-you-load-dds-textures-during-runtime.html#answer-707772
	// http://msdn.microsoft.com/en-us/library/bb943992.aspx
	// http://msdn.microsoft.com/en-us/library/windows/desktop/bb205578(v=vs.85).aspx
	// mipmapBias limits the number of mipmap when > 0
	public static Texture2D? LoadDDS(FileStream fileStream, out bool hasMipMaps)
	{
		hasMipMaps = false;
		using var reader = new BinaryReader(fileStream);

		if (!FourCcEquals(reader.ReadBytes(4), "DDS "))
		{
			error = "Invalid DDS file";
			return null;
		}

		//this header byte should be 124 for DDS image files
		if (reader.ReadUInt32() != 124u)
		{
			error = "Invalid header size";
			return null;
		}

		var dwFlags = reader.ReadUInt32();
		var dwHeight = (int)reader.ReadUInt32();
		var dwWidth = (int)reader.ReadUInt32();

		reader.ReadUInt64();
		var dwMipMapCount = reader.ReadUInt32();

		if ((dwFlags & DDSD_MIPMAPCOUNT_BIT) != 0)
			hasMipMaps = dwMipMapCount > 1u;

		// dwReserved1
		for (var i = 5; i-- > 0;)
			reader.ReadUInt64();
		
		reader.ReadUInt32();

		// DDS_PIXELFORMAT
		reader.ReadUInt32();
		var dds_pxlf_dwFlags = reader.ReadUInt32();
		var dds_pxlf_dwFourCC = reader.ReadBytes(4);
		// var fourCC = Encoding.ASCII.GetString(dds_pxlf_dwFourCC);
		var dds_pxlf_dwRGBBitCount = reader.ReadUInt32();
		var pixelSize = dds_pxlf_dwRGBBitCount / 8;
		var dds_pxlf_dwRBitMask = reader.ReadUInt32();
		var dds_pxlf_dwGBitMask = reader.ReadUInt32();
		var dds_pxlf_dwBBitMask = reader.ReadUInt32();
		var dds_pxlf_dwABitMask = reader.ReadUInt32();

		reader.ReadUInt64();
		reader.ReadUInt64();
		reader.ReadUInt32();

		var rgb888 = dds_pxlf_dwRBitMask == 0x000000ff
			&& dds_pxlf_dwGBitMask == 0x0000ff00
			&& dds_pxlf_dwBBitMask == 0x00ff0000;
		
		var bgr888 = dds_pxlf_dwRBitMask == 0x00ff0000
			&& dds_pxlf_dwGBitMask == 0x0000ff00
			&& dds_pxlf_dwBBitMask == 0x000000ff;
		
		var rgb565 = dds_pxlf_dwRBitMask == 0x0000F800
			&& dds_pxlf_dwGBitMask == 0x000007E0
			&& dds_pxlf_dwBBitMask == 0x0000001F;
		
		var argb4444 = dds_pxlf_dwABitMask == 0x0000f000
			&& dds_pxlf_dwRBitMask == 0x00000f00
			&& dds_pxlf_dwGBitMask == 0x000000f0
			&& dds_pxlf_dwBBitMask == 0x0000000f;
		
		var rbga4444 = dds_pxlf_dwABitMask == 0x0000000f
			&& dds_pxlf_dwRBitMask == 0x0000f000
			&& dds_pxlf_dwGBitMask == 0x000000f0
			&& dds_pxlf_dwBBitMask == 0x00000f00;
		
		var textureFormat = TextureFormat.ARGB32;
		var isCompressed = false;
		
		if ((dds_pxlf_dwFlags & DDPF_FOURCC) != 0)
		{
			// Texture does not contain RGB data, check FourCC for format
			isCompressed = true;

			if (FourCcEquals(dds_pxlf_dwFourCC, "DXT1"))
				textureFormat = TextureFormat.DXT1;
			else if (FourCcEquals(dds_pxlf_dwFourCC, "DXT5"))
				textureFormat = TextureFormat.DXT5;
			else if (FourCcEquals(dds_pxlf_dwFourCC, "DX10"))
				textureFormat = TextureFormat.BC7;
		}
		else
		{
			var alphapixel = (dds_pxlf_dwFlags & DDPF_ALPHAPIXELS) != 0;
			
			switch ((dds_pxlf_dwFlags & DDPF_RGB) != 0)
			{
				case true when rgb888 || bgr888:
					// RGB or RGBA format
					textureFormat = alphapixel
						? TextureFormat.RGBA32
						: TextureFormat.RGB24;
					break;
				case true when rgb565:
					// Nvidia texconv B5G6R5_UNORM
					textureFormat = TextureFormat.RGB565;
					break;
				case true when alphapixel && argb4444:
					// Nvidia texconv B4G4R4A4_UNORM
					textureFormat = TextureFormat.ARGB4444;
					break;
				case true when alphapixel && rbga4444:
					textureFormat = TextureFormat.RGBA4444;
					break;
				case false when (dds_pxlf_dwFlags & DDPF_ALPHA) != 0 != ((dds_pxlf_dwFlags & DDPF_LUMINANCE) != 0):
					// A8 format or Luminance 8
					textureFormat = TextureFormat.Alpha8;
					break;
				default:
					error = "Only BC7, DXT1, DXT5, A8, RGB24, BGR24, RGBA32, BGBR32, RGB565, ARGB4444 and "
						+ "RGBA4444 are supported";
					return null;
			}
		}

		var dataBias = (long)(textureFormat != TextureFormat.BC7 ? 128 : 148);
		var dxtBytesLength = reader.BaseStream.Length - dataBias;
		reader.BaseStream.Seek(dataBias, SeekOrigin.Begin);
		var dxtBytes = reader.ReadBytes((int)dxtBytesLength);

		// Swap red and blue.
		if (!isCompressed && bgr888)
		{
			for (uint i = 0; i < dxtBytes.Length; i += pixelSize)
			{
				var b = dxtBytes[i + 0];
				var r = dxtBytes[i + 2];

				dxtBytes[i + 0] = r;
				dxtBytes[i + 2] = b;
			}
		}

		// QualitySettings.masterTextureLimit = 0;
		// Work around for a >Unity< Bug.
		// if QualitySettings.masterTextureLimit != 0 (half or quarter texture rez)
		// and dwWidth and dwHeight divided by 2 (or 4 for quarter rez) are not a multiple of 4 
		// and we are creating a DXT5 or DXT1 texture
		// Then you get an Unity error on the "new Texture"

		var quality = QualitySettings.masterTextureLimit;

		// If the bug conditions are present then switch to full quality
		if (isCompressed && quality > 0 && (dwWidth >> quality) % 4 != 0 && (dwHeight >> quality) % 4 != 0)
			QualitySettings.masterTextureLimit = 0;

		var texture = new Texture2D(dwWidth, dwHeight, textureFormat, hasMipMaps);
		texture.LoadRawTextureData(dxtBytes);
		return texture;
	}

	private static bool FourCcEquals(IList<byte> bytes, string s)
		=> bytes.Count >= 4 && bytes[0] == s[0] && bytes[1] == s[1] && bytes[2] == s[2] && bytes[3] == s[3];
}