////////////////////////////////////////////////////////////
// Headers
////////////////////////////////////////////////////////////

/// GLEW is needed to provide OpenGL extensions.
#include <GL/glew.h>

#include <SFML/Graphics.hpp>
#include <SFML/OpenGL.hpp>

/// GLM is needed to provide 3D math properties, particularly matrices for 3D transformations.
#define GLM_ENABLE_EXPERIMENTAL
#include "glm/glm.hpp"
#include "glm/gtx/transform.hpp"

#include <iostream>

#ifndef GL_SRGB8_ALPHA8
#define GL_SRGB8_ALPHA8 0x8C43
#endif

///Basic vertex shader that transforms the vertex position based on a projection view matrix and passes the texture coordinate to the fragment shader.
const std::string defaultVertexShader =
"#version 330\n"\
"attribute vec3 position;"\
"attribute vec2 texCoord;" \
"uniform mat4 pvm;" \

"varying vec2 uv;" \

"void main() {"\
"	gl_Position = pvm * vec4(position, 1.0);"\
"	uv = texCoord;"\
"}";

///Basic fragment shader that returns the colour of a pixel based on the input texture and its coordinate.
const std::string defaultFragShader =
"#version 330\n" \
"uniform sampler2D texture;" \
"varying vec2 uv;" \

"void main() {" \
"	gl_FragColor = texture2D(texture, uv);" \
"}";

///Shader Types
enum class ShaderType { Vertex, Fragment, Geometry, Count };
///Standard Uniforms in the shader.
enum class UniformType { TransformPVM, Count };
///Vertex attributes for shaders and the input vertex array.
enum class VertexAttribute { Position, TexCoord, COUNT };

///Shader Program
GLuint program = 0;

///List of shaders set up for a 3D scene.
GLuint shader[static_cast<unsigned int>(ShaderType::Count)];
///List of uniforms that can be defined values for the shader.
GLint uniform[static_cast<unsigned int>(UniformType::Count)];

///Vertex Array Object ID.
GLuint vao = 0;
///Vertex Buffer Object for Vertices.
GLuint vertexVBO = 0;
///Vertex Buffer Object for Indices.
GLuint indexVBO = 0;
///Depending on input, the amount of vertices or indices that are needed to be drawn for this object.
unsigned int drawCount;

///Checks for any errors specific to the shaders. It will output any errors within the shader if it's not valid.
void checkError(GLuint l_shader, GLuint l_flag, bool l_program, const std::string& l_errorMsg)
{
	GLint success = 0;
	GLchar error[1024] = { 0 };
	if (l_program) { glGetProgramiv(l_shader, l_flag, &success); }
	else { glGetShaderiv(l_shader, l_flag, &success); }

	if (success) { return; }
	if (l_program) {
		glGetProgramInfoLog(l_shader, sizeof(error), nullptr, error);
	}
	else {
		glGetShaderInfoLog(l_shader, sizeof(error), nullptr, error);
	}

	std::cout << l_errorMsg << "\n";
}

///Creates and compiles a shader.
GLuint buildShader(const std::string& l_src, unsigned int l_type)
{
	GLuint shaderID = glCreateShader(l_type);
	if (!shaderID) {
		std::cout << "Bad shader type!";
		return 0;
	}
	const GLchar* sources[1];
	GLint lengths[1];
	sources[0] = l_src.c_str();
	lengths[0] = l_src.length();
	glShaderSource(shaderID, 1, sources, lengths);
	glCompileShader(shaderID);
	checkError(shaderID, GL_COMPILE_STATUS, false, "Shader compile error: ");
	return shaderID;
}

///Function to load the shaders from string data.
void LoadFromMemory(const std::string& shaderData, ShaderType type)
{
	if (shaderData.empty())
		return;

	if (shader[static_cast<unsigned int>(type)])
	{
		glDetachShader(program, shader[static_cast<unsigned int>(type)]);
		glDeleteShader(shader[static_cast<unsigned int>(type)]);
	}

	switch (type)
	{
	case ShaderType::Vertex:
		shader[static_cast<unsigned int>(type)] = buildShader(shaderData, GL_VERTEX_SHADER);
		break;
	case ShaderType::Geometry:
		shader[static_cast<unsigned int>(type)] = buildShader(shaderData, GL_GEOMETRY_SHADER);
		break;
	case ShaderType::Fragment:
		shader[static_cast<unsigned int>(type)] = buildShader(shaderData, GL_FRAGMENT_SHADER);
		break;
	default:
		break;
	}

	if (program == 0)
	{
		program = glCreateProgram();
	}

	glAttachShader(program, shader[static_cast<unsigned int>(type)]);
	glBindAttribLocation(program, static_cast<GLuint>(VertexAttribute::Position), "position");
	glBindAttribLocation(program, static_cast<GLuint>(VertexAttribute::TexCoord), "texCoord");

	glLinkProgram(program);
	checkError(program, GL_LINK_STATUS, true, "Shader link error:");
	glValidateProgram(program);
	checkError(program, GL_VALIDATE_STATUS, true, "Invalid shader:");

	uniform[static_cast<unsigned int>(UniformType::TransformPVM)] = glGetUniformLocation(program, "pvm");
}

////////////////////////////////////////////////////////////
/// Entry point of application
///
/// \return Application exit code
///
////////////////////////////////////////////////////////////
int main()
{
	bool exit = false;
	bool sRgb = false;

	while (!exit)
	{
		// Request a 24-bits depth buffer when creating the window
		sf::ContextSettings contextSettings;
		contextSettings.depthBits = 24;
		contextSettings.sRgbCapable = sRgb;

		// Create the main window
		sf::RenderWindow window(sf::VideoMode(800, 600), "SFML graphics with OpenGL", sf::Style::Default, contextSettings);
		window.setVerticalSyncEnabled(true);

		// Initialise GLEW for the extended functions.
		glewExperimental = GL_TRUE;
		if (glewInit() != GLEW_OK)
			return EXIT_FAILURE;

		// Create a sprite for the background
		sf::Texture backgroundTexture;
		backgroundTexture.setSrgb(sRgb);
		if (!backgroundTexture.loadFromFile("resources/background.jpg"))
			return EXIT_FAILURE;
		sf::Sprite background(backgroundTexture);

		// Create some text to draw on top of our OpenGL object
		sf::Font font;
		if (!font.loadFromFile("resources/sansation.ttf"))
			return EXIT_FAILURE;
		sf::Text text("SFML / OpenGL demo", font);
		sf::Text sRgbInstructions("Press space to toggle sRGB conversion", font);
		sf::Text mipmapInstructions("Press return to toggle mipmapping", font);
		text.setFillColor(sf::Color(255, 255, 255, 170));
		sRgbInstructions.setFillColor(sf::Color(255, 255, 255, 170));
		mipmapInstructions.setFillColor(sf::Color(255, 255, 255, 170));
		text.setPosition(250.f, 450.f);
		sRgbInstructions.setPosition(150.f, 500.f);
		mipmapInstructions.setPosition(180.f, 550.f);

		// Load a texture to apply to our 3D cube
		sf::Texture texture;
		if (!texture.loadFromFile("resources/texture.jpg"))
			return EXIT_FAILURE;

		// Attempt to generate a mipmap for our cube texture
		// We don't check the return value here since
		// mipmapping is purely optional in this example
		texture.generateMipmap();

		// Make the window the active window for OpenGL calls
		window.setActive(true);

		// Load the shaders we need.
		if (program == 0)
		{
			LoadFromMemory(defaultVertexShader, ShaderType::Vertex);
			LoadFromMemory(defaultFragShader, ShaderType::Fragment);
		}

		// Enable Z-buffer read and write and culling.
		glEnable(GL_DEPTH_TEST);
		glEnable(GL_CULL_FACE);
		glCullFace(GL_BACK);

		// Setup a perspective projection
		GLfloat ratio = static_cast<float>(window.getSize().x) / window.getSize().y;
		glm::mat4 projection = glm::frustum(-ratio, ratio, -1.f, 1.f, 1.f, 500.0f);

		// Define a 3D cube (6 faces made of 2 triangles composed by 3 indices of a list of vertices)
		static const GLfloat cube[] =
		{
			 // positions   // texture coordinates
			//front
			-20, -20, -20,  0, 0,
			 20, -20, -20,  1, 0,
			 20,  20, -20,  1, 1,
			-20,  20, -20,  0, 1,
			//right
			 20,  20, -20,  1, 1,
			 20,  20,  20,  0, 1,
			 20, -20,  20,  0, 0,
			 20, -20, -20,  1, 0,
			//back
			-20, -20,  20,  0, 0,
			 20, -20,  20,  1, 0,
			 20,  20,  20,  1, 1,
			-20,  20,  20,  0, 1,
			//left
			-20, -20,  20,  0, 0,
			-20, -20, -20,  1, 0,
			-20,  20, -20,  1, 1,
			-20,  20,  20,  0, 1,
			//upper
			 20, -20,  20,  0, 1,
			-20, -20,  20,  1, 1,
			-20, -20, -20,  1, 0,
			 20, -20, -20,  0, 0,
			//bottom
			-20,  20, -20,  0, 1,
			 20,  20, -20,  1, 1,
			 20,  20,  20,  1, 0,
			-20,  20,  20,  0, 0,
		};

		// Define indices for 3D cube.
		static const unsigned int indices[] =
		{
			2, 1, 0, 3, 2, 0, //front
			4, 5, 6, 4, 6, 7, //right
			8, 9, 10, 8, 10, 11, //back
			14, 13, 12, 15, 14, 12, //left
			16, 17, 18, 16, 18, 19, //upper
			22, 21, 20, 23, 22, 20  //bottom
		};

		// Stride is the number of bytes per array element.
		auto stride = sizeof(GLfloat) * 5;
		// Data offset for texture coordinate in bytes.
		auto textureCoordOffset = sizeof(GLfloat) * 3;
		// Amount of index elements in total.
		drawCount = sizeof(indices) / sizeof(unsigned int);


		// Generate Vertex Array and Vertex Buffer and point the area of data to assign to each attribute.
		glGenVertexArrays(1, &vao);
		glBindVertexArray(vao);
		glGenBuffers(1, &vertexVBO);
		glBindBuffer(GL_ARRAY_BUFFER, vertexVBO);
		glBufferData(GL_ARRAY_BUFFER, drawCount * stride, cube, GL_STATIC_DRAW);
		glEnableVertexAttribArray(static_cast<GLuint>(VertexAttribute::Position));
		glVertexAttribPointer(static_cast<GLuint>(VertexAttribute::Position), 3, GL_FLOAT, GL_FALSE, stride, 0);
		glEnableVertexAttribArray(static_cast<GLuint>(VertexAttribute::TexCoord));
		glVertexAttribPointer(static_cast<GLuint>(VertexAttribute::TexCoord), 2, GL_FLOAT, GL_FALSE, stride, (void*)textureCoordOffset);

		// Generate Index Buffer and define the amount of indices to point to.
		glGenBuffers(1, &indexVBO);
		glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, indexVBO);
		glBufferData(GL_ELEMENT_ARRAY_BUFFER, drawCount * sizeof(indices[0]), indices, GL_STATIC_DRAW);

		//Make sure to bind the vertex array to null if you wish to define more objects.
		glBindVertexArray(0);

		// Make the window no longer the active window for OpenGL calls
		window.setActive(false);

		// Create a clock for measuring the time elapsed
		sf::Clock clock;

		// Flag to track whether mipmapping is currently enabled
		bool mipmapEnabled = true;

		// Start game loop
		while (window.isOpen())
		{
			// Process events
			sf::Event event;
			while (window.pollEvent(event))
			{
				// Close window: exit
				if (event.type == sf::Event::Closed)
				{
					exit = true;
					window.close();
				}

				// Escape key: exit
				if ((event.type == sf::Event::KeyPressed) && (event.key.code == sf::Keyboard::Escape))
				{
					exit = true;
					window.close();
				}

				// Return key: toggle mipmapping
				if ((event.type == sf::Event::KeyPressed) && (event.key.code == sf::Keyboard::Return))
				{
					if (mipmapEnabled)
					{
						// We simply reload the texture to disable mipmapping
						if (!texture.loadFromFile("resources/texture.jpg"))
							return EXIT_FAILURE;

						mipmapEnabled = false;
					}
					else
					{
						texture.generateMipmap();

						mipmapEnabled = true;
					}
				}

				// Space key: toggle sRGB conversion
				if ((event.type == sf::Event::KeyPressed) && (event.key.code == sf::Keyboard::Space))
				{
					sRgb = !sRgb;
					window.close();
				}

				// Adjust the viewport when the window is resized
				if (event.type == sf::Event::Resized)
				{
					// Make the window the active window for OpenGL calls
					window.setActive(true);

					glViewport(0, 0, event.size.width, event.size.height);

					// Make the window no longer the active window for OpenGL calls
					window.setActive(false);
				}
			}

			// Clear the depth buffer
			glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

			// Configure the viewport (the same size as the window)
			glViewport(0, 0, window.getSize().x, window.getSize().y);

			// Draw the background
			window.pushGLStates();
			window.draw(background);
			window.popGLStates();

			// Make the window the active window for OpenGL calls
			window.setActive(true);

			// Bind the texture
			sf::Texture::bind(&texture);
			glBindVertexArray(vao);

			// We get the position of the mouse cursor, so that we can move the box accordingly
			float x = sf::Mouse::getPosition(window).x * 200.f / window.getSize().x - 100.f;
			float y = -sf::Mouse::getPosition(window).y * 200.f / window.getSize().y + 100.f;

			// Apply some transformations
			glm::mat4 matrix_pos = glm::translate(glm::vec3(x, y, -100.f));
			glm::mat4 matrix_rotX = glm::rotate(clock.getElapsedTime().asSeconds() * 50.f * (3.1415926f / 180.0f), glm::vec3(1.f, 0.f, 0.f));
			glm::mat4 matrix_rotY = glm::rotate(clock.getElapsedTime().asSeconds() * 30.f * (3.1415926f / 180.0f), glm::vec3(0.f, 1.f, 0.f));
			glm::mat4 matrix_rotZ = glm::rotate(clock.getElapsedTime().asSeconds() * 90.f * (3.1415926f / 180.0f), glm::vec3(0.f, 0.f, 1.f));

			glm::mat4 matrix_rotation = matrix_rotZ * matrix_rotY * matrix_rotX;
			glm::mat4 transform = matrix_pos * matrix_rotation;

			glm::mat4 identity;
			glm::mat4 viewProj = projection * transform;

			//Bind the shaders.
			glUseProgram(program);

			//Set the uniforms for the shader to use.
			if (uniform[(int)UniformType::TransformPVM] >= 0)
				glUniformMatrix4fv((unsigned int)uniform[(int)UniformType::TransformPVM], 1, GL_FALSE, &viewProj[0][0]);

			// Draw the cube
			glDrawElements(GL_TRIANGLES, drawCount, GL_UNSIGNED_INT, 0);

			// Reset the vertex array bound, shader and texture for other assets to draw.
			glBindVertexArray(0);
			glUseProgram(0);
			glBindTexture(GL_TEXTURE_2D, 0);

			// Make the window no longer the active window for OpenGL calls
			window.setActive(false);

			// Draw some text on top of our OpenGL object
			window.pushGLStates();
			window.draw(text);
			window.draw(sRgbInstructions);
			window.draw(mipmapInstructions);
			window.popGLStates();

			// Finally, display the rendered frame on screen
			window.display();
		}

		//Destroy all buffers, shaders and programs.
		glDeleteBuffers(1, &vertexVBO);
		glDeleteBuffers(1, &indexVBO);
		glDeleteVertexArrays(1, &vao);

		//Setting these values to zero will allow them to be initialised with new data on reset.
		vertexVBO = 0;
		indexVBO = 0;
		vao = 0;

		for (unsigned int i = 0; i < static_cast<unsigned int>(ShaderType::Count); i++)
		{
			glDetachShader(program, shader[i]);
			glDeleteShader(shader[i]);
			shader[i] = 0;
		}

		for (unsigned int i = 0; i < static_cast<unsigned int>(UniformType::Count); i++)
		{
			uniform[i] = -1;
		}

		glDeleteProgram(program);
		program = 0;
	}

	return EXIT_SUCCESS;
}