// HLSL -> SPIR-V (dxc) -> GLSL ES 3.00 (SPIRV-Cross.NET), for Blacklight.WebGL2's MainVS/MainPS.
// Not general-purpose: entry point names and vs/ps pairing are hardcoded to this one shader.
//
// usage: ShaderTranspiler <dxc.exe> <MainWebGL2.hlsl> <outputDir> [-I <includeDir>]...

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using SPIRVCross.NET;
using SPIRVCross.NET.GLSL;

static byte[] CompileToSpirv(string dxcPath, string sourcePath, string targetProfile, string entryPoint,
	List<string> includeDirectories, string tempDirectory)
{
	string outputSpirvPath = Path.Combine(tempDirectory, entryPoint + ".spv");

	var arguments = new List<string> { "-T", targetProfile, "-E", entryPoint, "-spirv", sourcePath, "-Fo", outputSpirvPath };
	foreach (string includeDirectory in includeDirectories)
	{
		arguments.Add("-I");
		arguments.Add(includeDirectory);
	}

	var startInfo = new ProcessStartInfo(dxcPath)
	{
		RedirectStandardError = true,
		RedirectStandardOutput = true,
		UseShellExecute = false,
	};
	
	foreach (string argument in arguments)
	{
		startInfo.ArgumentList.Add(argument);
	}

	using var process = Process.Start(startInfo)!;
	string stderr = process.StandardError.ReadToEnd();
	string stdout = process.StandardOutput.ReadToEnd();
	process.WaitForExit();

	if (process.ExitCode != 0)
	{
		throw new InvalidOperationException($"dxc failed compiling {entryPoint} ({targetProfile}):\n{stdout}\n{stderr}");
	}

	return File.ReadAllBytes(outputSpirvPath);
}

static string CrossCompileToGlslEs(byte[] spirv, string interfacePrefixToStrip)
{
	using var context = new Context();
	ParsedIR parsedIr = context.ParseSpirv(spirv);
	GLSLCrossCompiler compiler = context.CreateGLSLCompiler(parsedIr);

	compiler.glslOptions.version = 300;
	compiler.glslOptions.ES = true;

	// GLSL has no separate Texture2D/SamplerState objects, so combine each declared pair into one
	// sampler2D before compiling.
	compiler.BuildCombinedImageSamplers();
	RenameCombinedSamplersByOriginalBinding(compiler);

	compiler.options.fixupClipSpace = false;
	compiler.options.flipVertexY = false;

	// The vertex and fragment stages are cross-compiled independently, and SPIRVCross.NET names each
	// stage's interface variables from its own direction (out_var_COLOR0 vs in_var_COLOR0) rather than
	// a name shared across the pipeline.  GLSL links varyings by exact name when neither side gives an
	// explicit layout(location), so stripping the boundary-facing prefix down to the bare HLSL semantic
	// (COLOR0, TEXCOORD1, ...) makes the two stages agree.
	return compiler.Compile().Replace(interfacePrefixToStrip, "");
}

static void RenameCombinedSamplersByOriginalBinding(Compiler compiler)
{
	foreach (CombinedImageSampler combined in compiler.GetCombinedImageSamplers())
	{
		uint slot = compiler.GetDecoration(combined.image_id, Decoration.Binding);
		compiler.SetName(combined.combined_id, $"uTexture{slot}");
	}
}

if (args.Length < 3)
{
	Console.Error.WriteLine("usage: ShaderTranspiler <dxc.exe> <source.hlsl> <outputDir> [-I <includeDir>]...");
	return 1;
}

string dxcPath = args[0];
string sourcePath = args[1];
string outputDirectory = args[2];
var includeDirectories = new List<string>();
for (int i = 3; i < args.Length; ++i)
{
	if (args[i] == "-I" && i + 1 < args.Length)
	{
		includeDirectories.Add(args[++i]);
	}
}

string tempDirectory = Path.Combine(Path.GetTempPath(), "Blacklight.WebGL2.ShaderTranspiler." + Guid.NewGuid().ToString("N"));
Directory.CreateDirectory(tempDirectory);
try
{
	byte[] vertexSpirv = CompileToSpirv(dxcPath, sourcePath, "vs_6_0", "MainVS", includeDirectories, tempDirectory);
	byte[] fragmentSpirv = CompileToSpirv(dxcPath, sourcePath, "ps_6_0", "MainPS", includeDirectories, tempDirectory);

	string vertexGlsl = CrossCompileToGlslEs(vertexSpirv, interfacePrefixToStrip: "out_var_");
	string fragmentGlsl = CrossCompileToGlslEs(fragmentSpirv, interfacePrefixToStrip: "in_var_");

	Directory.CreateDirectory(outputDirectory);
	File.WriteAllText(Path.Combine(outputDirectory, "Main.vert.glsl"), vertexGlsl);
	File.WriteAllText(Path.Combine(outputDirectory, "Main.frag.glsl"), fragmentGlsl);
}
finally
{
	Directory.Delete(tempDirectory, recursive: true);
}

return 0;