#include "RuntimeShaderRenderer.h"

#include <array>
#include <cstring>
#include <string>

namespace
{
constexpr GLuint kGlobalParamsBindingPoint = 0;

const char* kVertexShaderSource = R"GLSL(
#version 430 core
out vec2 vTexCoord;
void main()
{
	vec2 positions[3] = vec2[3](
		vec2(-1.0, -1.0),
		vec2( 3.0, -1.0),
		vec2(-1.0,  3.0));
	vec2 texCoords[3] = vec2[3](
		vec2(0.0, 0.0),
		vec2(2.0, 0.0),
		vec2(0.0, 2.0));
	gl_Position = vec4(positions[gl_VertexID], 0.0, 1.0);
	vTexCoord = texCoords[gl_VertexID];
}
)GLSL";

struct GlobalParamsStd140
{
	float time = 0.0f;
	float pad0 = 0.0f;
	float inputResolution[2] = {};
	float outputResolution[2] = {};
	float utcTimeSeconds = 0.0f;
	float utcOffsetSeconds = 0.0f;
	float startupRandom = 0.37f;
	float frameCount = 0.0f;
	float mixAmount = 1.0f;
	float bypass = 0.0f;
	int sourceHistoryLength = 0;
	int temporalHistoryLength = 0;
	int feedbackAvailable = 0;
	float speed = 1.0f;
	float scale = 1.0f;
	float raySteps = 77.0f;
	float intensity = 1.0f;
	float sourceMix = 0.0f;
	float pad1[3] = {};
};
}

RuntimeShaderRenderer::~RuntimeShaderRenderer()
{
	ShutdownGl();
}

bool RuntimeShaderRenderer::CommitFragmentShader(const std::string& fragmentShaderSource, std::string& error)
{
	if (fragmentShaderSource.empty())
	{
		error = "Cannot commit an empty fragment shader.";
		return false;
	}

	if (!EnsureStaticGlResources(error))
		return false;

	GLuint vertexShader = 0;
	GLuint fragmentShader = 0;
	GLuint program = 0;
	if (!CompileShader(GL_VERTEX_SHADER, kVertexShaderSource, vertexShader, error))
		return false;
	if (!CompileShader(GL_FRAGMENT_SHADER, fragmentShaderSource.c_str(), fragmentShader, error))
	{
		glDeleteShader(vertexShader);
		return false;
	}

	program = glCreateProgram();
	glAttachShader(program, vertexShader);
	glAttachShader(program, fragmentShader);
	glLinkProgram(program);

	GLint linkResult = GL_FALSE;
	glGetProgramiv(program, GL_LINK_STATUS, &linkResult);
	if (linkResult == GL_FALSE)
	{
		std::array<char, 4096> log = {};
		GLsizei length = 0;
		glGetProgramInfoLog(program, static_cast<GLsizei>(log.size()), &length, log.data());
		error = std::string(log.data(), static_cast<std::size_t>(length));
		glDeleteProgram(program);
		glDeleteShader(vertexShader);
		glDeleteShader(fragmentShader);
		return false;
	}

	const GLuint globalParamsIndex = glGetUniformBlockIndex(program, "GlobalParams");
	if (globalParamsIndex != GL_INVALID_INDEX)
		glUniformBlockBinding(program, globalParamsIndex, kGlobalParamsBindingPoint);

	glUseProgram(program);
	const GLint videoInputLocation = glGetUniformLocation(program, "gVideoInput");
	if (videoInputLocation >= 0)
		glUniform1i(videoInputLocation, 0);
	const GLint layerInputLocation = glGetUniformLocation(program, "gLayerInput");
	if (layerInputLocation >= 0)
		glUniform1i(layerInputLocation, 0);
	glUseProgram(0);

	DestroyProgram();
	mProgram = program;
	mVertexShader = vertexShader;
	mFragmentShader = fragmentShader;
	return true;
}

void RuntimeShaderRenderer::RenderFrame(uint64_t frameIndex, unsigned width, unsigned height)
{
	if (mProgram == 0)
		return;

	GlobalParamsStd140 params;
	params.time = static_cast<float>(frameIndex) / 60.0f;
	params.inputResolution[0] = static_cast<float>(width);
	params.inputResolution[1] = static_cast<float>(height);
	params.outputResolution[0] = static_cast<float>(width);
	params.outputResolution[1] = static_cast<float>(height);
	params.frameCount = static_cast<float>(frameIndex);

	glViewport(0, 0, static_cast<GLsizei>(width), static_cast<GLsizei>(height));
	glDisable(GL_SCISSOR_TEST);
	glDisable(GL_DEPTH_TEST);
	glDisable(GL_BLEND);
	glBindBuffer(GL_UNIFORM_BUFFER, mGlobalParamsBuffer);
	glBufferSubData(GL_UNIFORM_BUFFER, 0, sizeof(params), &params);
	glBindBufferBase(GL_UNIFORM_BUFFER, kGlobalParamsBindingPoint, mGlobalParamsBuffer);
	glBindBuffer(GL_UNIFORM_BUFFER, 0);
	glBindVertexArray(mVertexArray);
	glUseProgram(mProgram);
	glDrawArrays(GL_TRIANGLES, 0, 3);
	glUseProgram(0);
	glBindVertexArray(0);
}

void RuntimeShaderRenderer::ShutdownGl()
{
	DestroyProgram();
	DestroyStaticGlResources();
}

bool RuntimeShaderRenderer::EnsureStaticGlResources(std::string& error)
{
	if (mVertexArray == 0)
		glGenVertexArrays(1, &mVertexArray);
	if (mGlobalParamsBuffer == 0)
	{
		glGenBuffers(1, &mGlobalParamsBuffer);
		glBindBuffer(GL_UNIFORM_BUFFER, mGlobalParamsBuffer);
		glBufferData(GL_UNIFORM_BUFFER, static_cast<GLsizeiptr>(sizeof(GlobalParamsStd140)), nullptr, GL_DYNAMIC_DRAW);
		glBindBuffer(GL_UNIFORM_BUFFER, 0);
	}

	if (mVertexArray == 0 || mGlobalParamsBuffer == 0)
	{
		error = "Failed to create runtime shader GL resources.";
		return false;
	}
	return true;
}

bool RuntimeShaderRenderer::CompileShader(GLenum shaderType, const char* source, GLuint& shader, std::string& error) const
{
	shader = glCreateShader(shaderType);
	glShaderSource(shader, 1, &source, nullptr);
	glCompileShader(shader);

	GLint compileResult = GL_FALSE;
	glGetShaderiv(shader, GL_COMPILE_STATUS, &compileResult);
	if (compileResult != GL_FALSE)
		return true;

	std::array<char, 4096> log = {};
	GLsizei length = 0;
	glGetShaderInfoLog(shader, static_cast<GLsizei>(log.size()), &length, log.data());
	error = std::string(log.data(), static_cast<std::size_t>(length));
	glDeleteShader(shader);
	shader = 0;
	return false;
}

void RuntimeShaderRenderer::DestroyProgram()
{
	if (mProgram != 0)
		glDeleteProgram(mProgram);
	if (mVertexShader != 0)
		glDeleteShader(mVertexShader);
	if (mFragmentShader != 0)
		glDeleteShader(mFragmentShader);
	mProgram = 0;
	mVertexShader = 0;
	mFragmentShader = 0;
}

void RuntimeShaderRenderer::DestroyStaticGlResources()
{
	if (mGlobalParamsBuffer != 0)
		glDeleteBuffers(1, &mGlobalParamsBuffer);
	if (mVertexArray != 0)
		glDeleteVertexArrays(1, &mVertexArray);
	mGlobalParamsBuffer = 0;
	mVertexArray = 0;
}