using System;
using System.IO;
using System.Runtime.InteropServices;
using RefreshCS;

namespace Nerfed.Runtime.Graphics;

public static class ImageUtils
{
	/// <summary>
	/// Gets pointer to pixel data from compressed image byte data.
	///
	/// The returned pointer must be freed by calling FreePixelData.
	/// </summary>
	public static unsafe byte* GetPixelDataFromBytes(
		Span<byte> data,
		out uint width,
		out uint height,
		out uint sizeInBytes
	) {
		fixed (byte* ptr = data)
		{
			byte* pixelData =
				Refresh.Refresh_Image_Load(
				ptr,
				data.Length,
				out int w,
				out int h,
				out int len
			);

			width = (uint) w;
			height = (uint) h;
			sizeInBytes = (uint) len;

			return pixelData;
		}
	}

	/// <summary>
	/// Gets pointer to pixel data from a compressed image stream.
	///
	/// The returned pointer must be freed by calling FreePixelData.
	/// </summary>
	public static unsafe byte* GetPixelDataFromStream(
		Stream stream,
		out uint width,
		out uint height,
		out uint sizeInBytes
	) {
		long length = stream.Length;
		void* buffer = NativeMemory.Alloc((nuint) length);
		Span<byte> span = new Span<byte>(buffer, (int) length);
		stream.ReadExactly(span);

		byte* pixelData = GetPixelDataFromBytes(span, out width, out height, out sizeInBytes);

		NativeMemory.Free(buffer);

		return pixelData;
	}

	/// <summary>
	/// Gets pointer to pixel data from a compressed image file.
	///
	/// The returned pointer must be freed by calling FreePixelData.
	/// </summary>
	public static unsafe byte* GetPixelDataFromFile(
		string path,
		out uint width,
		out uint height,
		out uint sizeInBytes
	) {
		FileStream fileStream = new FileStream(path, FileMode.Open, FileAccess.Read);
		return GetPixelDataFromStream(fileStream, out width, out height, out sizeInBytes);
	}

	/// <summary>
	/// Get metadata from compressed image bytes.
	/// </summary>
	public static unsafe bool ImageInfoFromBytes(
		Span<byte> data,
		out uint width,
		out uint height,
		out uint sizeInBytes
	) {
		fixed (byte* ptr = data)
		{
			int result =
				Refresh.Refresh_Image_Info(
				ptr,
				data.Length,
				out int w,
				out int h,
				out int len
			);

			width = (uint) w;
			height = (uint) h;
			sizeInBytes = (uint) len;

			return Conversions.IntToBool(result);
		}
	}

	/// <summary>
	/// Get metadata from a compressed image stream.
	/// </summary>
	public static unsafe bool ImageInfoFromStream(
		Stream stream,
		out uint width,
		out uint height,
		out uint sizeInBytes
	) {
		long length = stream.Length;
		void* buffer = NativeMemory.Alloc((nuint) length);
		Span<byte> span = new Span<byte>(buffer, (int) length);
		stream.ReadExactly(span);

		bool result = ImageInfoFromBytes(span, out width, out height, out sizeInBytes);

		NativeMemory.Free(buffer);

		return result;
	}

	/// <summary>
	/// Get metadata from a compressed image file.
	/// </summary>
	public static bool ImageInfoFromFile(
		string path,
		out uint width,
		out uint height,
		out uint sizeInBytes
	) {
		FileStream fileStream = new FileStream(path, FileMode.Open, FileAccess.Read);
		return ImageInfoFromStream(fileStream, out width, out height, out sizeInBytes);
	}

	/// <summary>
	/// Frees pixel data obtained from GetPixelData methods.
	/// </summary>
	public unsafe static void FreePixelData(byte* pixels)
	{
		Refresh.Refresh_Image_Free(pixels);
	}

	/// <summary>
	/// Saves pixel data contained in a TransferBuffer to a PNG file.
	/// </summary>
	public static unsafe void SavePNG(
		string path,
		TransferBuffer transferBuffer,
		uint bufferOffsetInBytes,
		int width,
		int height,
		bool bgra
	) {
		int sizeInBytes = width * height * 4;

		byte* pixelsPtr = (byte*) NativeMemory.Alloc((nuint) sizeInBytes);
		Span<byte> pixelsSpan = new Span<byte>(pixelsPtr, sizeInBytes);

		transferBuffer.GetData(pixelsSpan, bufferOffsetInBytes);

		if (bgra)
		{
			// if data is bgra, we have to swap the R and B channels
			byte* rgbaPtr = (byte*) NativeMemory.Alloc((nuint) sizeInBytes);
			Span<byte> rgbaSpan = new Span<byte>(rgbaPtr, sizeInBytes);

			for (int i = 0; i < sizeInBytes; i += 4)
			{
				rgbaSpan[i] = pixelsSpan[i + 2];
				rgbaSpan[i + 1] = pixelsSpan[i + 1];
				rgbaSpan[i + 2] = pixelsSpan[i];
				rgbaSpan[i + 3] = pixelsSpan[i + 3];
			}

			NativeMemory.Free(pixelsPtr);
			pixelsPtr = rgbaPtr;
		}

		Refresh.Refresh_Image_SavePNG(path, pixelsPtr, width, height);
		NativeMemory.Free(pixelsPtr);
	}

	// DDS loading extension, based on MojoDDS
	// Taken from https://github.com/FNA-XNA/FNA/blob/1e49f868f595f62bc6385db45949a03186a7cd7f/src/Graphics/Texture.cs#L194
	public static void ParseDDS(
		BinaryReader reader,
		out TextureFormat format,
		out int width,
		out int height,
		out int levels,
		out bool isCube
	) {
		// A whole bunch of magic numbers, yay DDS!
		const uint DDS_MAGIC = 0x20534444;
		const uint DDS_HEADERSIZE = 124;
		const uint DDS_PIXFMTSIZE = 32;
		const uint DDSD_HEIGHT = 0x2;
		const uint DDSD_WIDTH = 0x4;
		const uint DDSD_PITCH = 0x8;
		const uint DDSD_LINEARSIZE = 0x80000;
		const uint DDSD_REQ = (
			DDSD_HEIGHT | DDSD_WIDTH
		);
		const uint DDSCAPS_MIPMAP = 0x400000;
		const uint DDSCAPS_TEXTURE = 0x1000;
		const uint DDSCAPS2_CUBEMAP = 0x200;
		const uint DDPF_FOURCC = 0x4;
		const uint DDPF_RGB = 0x40;
		const uint FOURCC_DXT1 = 0x31545844;
		const uint FOURCC_DXT3 = 0x33545844;
		const uint FOURCC_DXT5 = 0x35545844;
		const uint FOURCC_DX10 = 0x30315844;
		const uint pitchAndLinear = (
			DDSD_PITCH | DDSD_LINEARSIZE
		);

		// File should start with 'DDS '
		if (reader.ReadUInt32() != DDS_MAGIC)
		{
			throw new NotSupportedException("Not a DDS!");
		}

		// Texture info
		uint size = reader.ReadUInt32();
		if (size != DDS_HEADERSIZE)
		{
			throw new NotSupportedException("Invalid DDS header!");
		}
		uint flags = reader.ReadUInt32();
		if ((flags & DDSD_REQ) != DDSD_REQ)
		{
			throw new NotSupportedException("Invalid DDS flags!");
		}
		if ((flags & pitchAndLinear) == pitchAndLinear)
		{
			throw new NotSupportedException("Invalid DDS flags!");
		}
		height = reader.ReadInt32();
		width = reader.ReadInt32();
		reader.ReadUInt32(); // dwPitchOrLinearSize, unused
		reader.ReadUInt32(); // dwDepth, unused
		levels = reader.ReadInt32();

		// "Reserved"
		reader.ReadBytes(4 * 11);

		// Format info
		uint formatSize = reader.ReadUInt32();
		if (formatSize != DDS_PIXFMTSIZE)
		{
			throw new NotSupportedException("Bogus PIXFMTSIZE!");
		}
		uint formatFlags = reader.ReadUInt32();
		uint formatFourCC = reader.ReadUInt32();
		uint formatRGBBitCount = reader.ReadUInt32();
		uint formatRBitMask = reader.ReadUInt32();
		uint formatGBitMask = reader.ReadUInt32();
		uint formatBBitMask = reader.ReadUInt32();
		uint formatABitMask = reader.ReadUInt32();

		// dwCaps "stuff"
		uint caps = reader.ReadUInt32();
		if ((caps & DDSCAPS_TEXTURE) == 0)
		{
			throw new NotSupportedException("Not a texture!");
		}

		isCube = false;

		uint caps2 = reader.ReadUInt32();
		if (caps2 != 0)
		{
			if ((caps2 & DDSCAPS2_CUBEMAP) == DDSCAPS2_CUBEMAP)
			{
				isCube = true;
			}
			else
			{
				throw new NotSupportedException("Invalid caps2!");
			}
		}

		reader.ReadUInt32(); // dwCaps3, unused
		reader.ReadUInt32(); // dwCaps4, unused

		// "Reserved"
		reader.ReadUInt32();

		// Mipmap sanity check
		if ((caps & DDSCAPS_MIPMAP) != DDSCAPS_MIPMAP)
		{
			levels = 1;
		}

		// Determine texture format
		if ((formatFlags & DDPF_FOURCC) == DDPF_FOURCC)
		{
			switch (formatFourCC)
			{
				case 0x71: // D3DFMT_A16B16G16R16F
					format = TextureFormat.R16G16B16A16_SFLOAT;
					break;
				case 0x74: // D3DFMT_A32B32G32R32F
					format = TextureFormat.R32G32B32A32_SFLOAT;
					break;
				case FOURCC_DXT1:
					format = TextureFormat.BC1;
					break;
				case FOURCC_DXT3:
					format = TextureFormat.BC2;
					break;
				case FOURCC_DXT5:
					format = TextureFormat.BC3;
					break;
				case FOURCC_DX10:
					// If the fourCC is DX10, there is an extra header with additional format information.
					uint dxgiFormat = reader.ReadUInt32();

					// These values are taken from the DXGI_FORMAT enum.
					switch (dxgiFormat)
					{
						case 2:
							format = TextureFormat.R32G32B32A32_SFLOAT;
							break;

						case 10:
							format = TextureFormat.R16G16B16A16_SFLOAT;
							break;

						case 71:
							format = TextureFormat.BC1;
							break;

						case 74:
							format = TextureFormat.BC2;
							break;

						case 77:
							format = TextureFormat.BC3;
							break;

						case 98:
							format = TextureFormat.BC7;
							break;

						default:
							throw new NotSupportedException(
								"Unsupported DDS texture format"
							);
					}

					uint resourceDimension = reader.ReadUInt32();

					// These values are taken from the D3D10_RESOURCE_DIMENSION enum.
					switch (resourceDimension)
					{
						case 0: // Unknown
						case 1: // Buffer
							throw new NotSupportedException(
								"Unsupported DDS texture format"
							);
						default:
							break;
					}

					/*
					 * This flag seemingly only indicates if the texture is a cube map.
					 * This is already determined above. Cool!
					 */
					uint miscFlag = reader.ReadUInt32();

					/*
					 * Indicates the number of elements in the texture array.
					 * We don't support texture arrays so just throw if it's greater than 1.
					 */
					uint arraySize = reader.ReadUInt32();

					if (arraySize > 1)
					{
						throw new NotSupportedException(
							"Unsupported DDS texture format"
						);
					}

					reader.ReadUInt32(); // reserved

					break;
				default:
					throw new NotSupportedException(
						"Unsupported DDS texture format"
					);
			}
		}
		else if ((formatFlags & DDPF_RGB) == DDPF_RGB)
		{
			if (	formatRGBBitCount != 32 ||
				formatRBitMask != 0x00FF0000 ||
				formatGBitMask != 0x0000FF00 ||
				formatBBitMask != 0x000000FF ||
				formatABitMask != 0xFF000000	)
			{
				throw new NotSupportedException(
					"Unsupported DDS texture format"
				);
			}

			format = TextureFormat.B8G8R8A8;
		}
		else
		{
			throw new NotSupportedException(
				"Unsupported DDS texture format"
			);
		}
	}

	public static int CalculateDDSLevelSize(
		int width,
		int height,
		TextureFormat format
	) {
		if (format == TextureFormat.R8G8B8A8)
		{
			return (((width * 32) + 7) / 8) * height;
		}
		else if (format == TextureFormat.R16G16B16A16_SFLOAT)
		{
			return (((width * 64) + 7) / 8) * height;
		}
		else if (format == TextureFormat.R32G32B32A32_SFLOAT)
		{
			return (((width * 128) + 7) / 8) * height;
		}
		else
		{
			int blockSize = 16;
			if (format == TextureFormat.BC1)
			{
				blockSize = 8;
			}
			width = System.Math.Max(width, 1);
			height = System.Math.Max(height, 1);
			return (
				((width + 3) / 4) *
				((height + 3) / 4) *
				blockSize
			);
		}
	}
}