#include <glad/glad.h>
#include <GLFW/glfw3.h>

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>

#include <learnopengl/shader_m.h>
#include <learnopengl/camera.h>

#include <iostream>

void framebuffer_size_callback(GLFWwindow* window, int width, int height);
void mouse_callback(GLFWwindow* window, double xpos, double ypos);
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset);
void process_input(GLFWwindow *window);
glm::mat4 calculate_model_matrix(const glm::vec3& position, const glm::vec3& rotation = glm::vec3(0.0f), const glm::vec3& scale = glm::vec3(1.0f));

// settings
const unsigned int SCR_WIDTH = 800;
const unsigned int SCR_HEIGHT = 600;

// camera
Camera camera(glm::vec3(0.0f, 0.0f, 5.0f));
float lastX = (float)SCR_WIDTH / 2.0;
float lastY = (float)SCR_HEIGHT / 2.0;
bool firstMouse = true;

// timing
float deltaTime = 0.0f;
float lastFrame = 0.0f;

int main(int argc, char* argv[])
{
	// glfw: initialize and configure
	// ------------------------------
	glfwInit();
	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 4);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	#ifdef __APPLE__
		glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
	#endif

	// glfw window creation
	// --------------------
	GLFWwindow* window = glfwCreateWindow(SCR_WIDTH, SCR_HEIGHT, "LearnOpenGL", NULL, NULL);
	if (window == NULL)
	{
		std::cout << "Failed to create GLFW window" << std::endl;
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);
	glfwSetFramebufferSizeCallback(window, framebuffer_size_callback);
	glfwSetCursorPosCallback(window, mouse_callback);
	glfwSetScrollCallback(window, scroll_callback);

	// tell GLFW to capture our mouse
	glfwSetInputMode(window, GLFW_CURSOR, GLFW_CURSOR_DISABLED);

	// glad: load all OpenGL function pointers
	// ---------------------------------------
	if (!gladLoadGLLoader((GLADloadproc)glfwGetProcAddress))
	{
		std::cout << "Failed to initialize GLAD" << std::endl;
		return -1;
	}

	// build and compile shaders
	// -------------------------
	Shader solidShader("solid.vs", "solid.fs");
	Shader transparentShader("transparent.vs", "transparent.fs");
	Shader compositeShader("composite.vs", "composite.fs");
	Shader screenShader("screen.vs", "screen.fs");

	// set up vertex data (and buffer(s)) and configure vertex attributes
	// ------------------------------------------------------------------
	float quadVertices[] = {
		// positions		// uv
		-1.0f, -1.0f, 0.0f,	0.0f, 0.0f,
		 1.0f, -1.0f, 0.0f, 1.0f, 0.0f,
		 1.0f,  1.0f, 0.0f, 1.0f, 1.0f,

		 1.0f,  1.0f, 0.0f, 1.0f, 1.0f,
		-1.0f,  1.0f, 0.0f, 0.0f, 1.0f,
		-1.0f, -1.0f, 0.0f, 0.0f, 0.0f
	};

	// quad VAO
	unsigned int quadVAO, quadVBO;
	glGenVertexArrays(1, &quadVAO);
	glGenBuffers(1, &quadVBO);
	glBindVertexArray(quadVAO);
	glBindBuffer(GL_ARRAY_BUFFER, quadVBO);
	glBufferData(GL_ARRAY_BUFFER, sizeof(quadVertices), quadVertices, GL_STATIC_DRAW);
	glEnableVertexAttribArray(0);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)0);
	glEnableVertexAttribArray(1);
	glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(float), (void*)(3 * sizeof(float)));
	glBindVertexArray(0);

	// set up framebuffers and their texture attachments
	// ------------------------------------------------------------------
	unsigned int opaqueFBO, transparentFBO;
	glGenFramebuffers(1, &opaqueFBO);
	glGenFramebuffers(1, &transparentFBO);

	// set up attachments for opaque framebuffer
	unsigned int opaqueTexture;
	glGenTextures(1, &opaqueTexture);
	glBindTexture(GL_TEXTURE_2D, opaqueTexture);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGBA, GL_HALF_FLOAT, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glBindTexture(GL_TEXTURE_2D, 0);

	unsigned int depthTexture;
	glGenTextures(1, &depthTexture);
	glBindTexture(GL_TEXTURE_2D, depthTexture);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, SCR_WIDTH, SCR_HEIGHT, 0, GL_DEPTH_COMPONENT, GL_FLOAT, NULL);
	glBindTexture(GL_TEXTURE_2D, 0);

	glBindFramebuffer(GL_FRAMEBUFFER, opaqueFBO);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, opaqueTexture, 0);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, depthTexture, 0);
	
	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
		std::cout << "ERROR::FRAMEBUFFER:: Opaque framebuffer is not complete!" << std::endl;

	glBindFramebuffer(GL_FRAMEBUFFER, 0);

	// set up attachments for transparent framebuffer
	unsigned int accumTexture;
	glGenTextures(1, &accumTexture);
	glBindTexture(GL_TEXTURE_2D, accumTexture);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA16F, SCR_WIDTH, SCR_HEIGHT, 0, GL_RGBA, GL_HALF_FLOAT, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glBindTexture(GL_TEXTURE_2D, 0);

	unsigned int revealTexture;
	glGenTextures(1, &revealTexture);
	glBindTexture(GL_TEXTURE_2D, revealTexture);
	glTexImage2D(GL_TEXTURE_2D, 0, GL_R8, SCR_WIDTH, SCR_HEIGHT, 0, GL_RED, GL_FLOAT, NULL);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
	glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
	glBindTexture(GL_TEXTURE_2D, 0);

	glBindFramebuffer(GL_FRAMEBUFFER, transparentFBO);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, accumTexture, 0);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, GL_TEXTURE_2D, revealTexture, 0);
	glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, depthTexture, 0); // opaque framebuffer's depth texture

	const GLenum transparentDrawBuffers[] = { GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1 };
	glDrawBuffers(2, transparentDrawBuffers);

	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
		std::cout << "ERROR::FRAMEBUFFER:: Transparent framebuffer is not complete!" << std::endl;

	glBindFramebuffer(GL_FRAMEBUFFER, 0);

	// set up transformation matrices
	// ------------------------------------------------------------------
	glm::mat4 redModelMat = calculate_model_matrix(glm::vec3(0.0f, 0.0f, 1.0f));
	glm::mat4 greenModelMat = calculate_model_matrix(glm::vec3(0.0f, 0.0f, 0.0f));
	glm::mat4 blueModelMat = calculate_model_matrix(glm::vec3(0.0f, 0.0f, 2.0f));

	// set up intermediate variables
	// ------------------------------------------------------------------
	glm::vec4 zeroFillerVec(0.0f);
	glm::vec4 oneFillerVec(1.0f);
	
	// render loop
	// -----------
	while (!glfwWindowShouldClose(window))
	{
		// per-frame time logic
		// --------------------
		float currentFrame = glfwGetTime();
		deltaTime = currentFrame - lastFrame;
		lastFrame = currentFrame;

		// camera matrices
		glm::mat4 projection = glm::perspective(glm::radians(camera.Zoom), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f);
		glm::mat4 view = camera.GetViewMatrix();
		glm::mat4 vp = projection * view;

		// input
		// -----
		process_input(window);

		// render
		// ------

		// draw solid objects (solid pass)
		// ------

		// configure render states
		glEnable(GL_DEPTH_TEST);
		glDepthFunc(GL_LESS);
		glDepthMask(GL_TRUE);
		glDisable(GL_BLEND);
		glClearColor(0.0f, 0.0f, 0.0f, 0.0f);

		// bind opaque framebuffer to render solid objects
		glBindFramebuffer(GL_FRAMEBUFFER, opaqueFBO);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

		// use solid shader
		solidShader.use();

		// draw red quad
		solidShader.setMat4("mvp", vp * redModelMat);
		solidShader.setVec3("color", glm::vec3(1.0f, 0.0f, 0.0f));
		glBindVertexArray(quadVAO);
		glDrawArrays(GL_TRIANGLES, 0, 6);

		// draw transparent objects (transparent pass)
		// -----

		// configure render states
		glDepthMask(GL_FALSE);
		glEnable(GL_BLEND);
		glBlendFunci(0, GL_ONE, GL_ONE);
		glBlendFunci(1, GL_ZERO, GL_ONE_MINUS_SRC_COLOR);
		glBlendEquation(GL_FUNC_ADD);

		// bind transparent framebuffer to render transparent objects
		glBindFramebuffer(GL_FRAMEBUFFER, transparentFBO);
		glClearBufferfv(GL_COLOR, 0, &zeroFillerVec[0]);
		glClearBufferfv(GL_COLOR, 1, &oneFillerVec[0]);

		// use transparent shader
		transparentShader.use();

		// draw green quad
		transparentShader.setMat4("mvp", vp * greenModelMat);
		transparentShader.setVec4("color", glm::vec4(0.0f, 1.0f, 0.0f, 0.5f));
		glBindVertexArray(quadVAO);
		glDrawArrays(GL_TRIANGLES, 0, 6);

		// draw blue quad
		transparentShader.setMat4("mvp", vp * blueModelMat);
		transparentShader.setVec4("color", glm::vec4(0.0f, 0.0f, 1.0f, 0.5f));
		glBindVertexArray(quadVAO);
		glDrawArrays(GL_TRIANGLES, 0, 6);

		// draw composite image (composite pass)
		// -----

		// set render states
		glDepthFunc(GL_ALWAYS);
		glEnable(GL_BLEND);
		glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);

		// bind opaque framebuffer
		glBindFramebuffer(GL_FRAMEBUFFER, opaqueFBO);

		// use composite shader
		compositeShader.use();

		// draw screen quad
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, accumTexture);
		glActiveTexture(GL_TEXTURE1);
		glBindTexture(GL_TEXTURE_2D, revealTexture);
		glBindVertexArray(quadVAO);
		glDrawArrays(GL_TRIANGLES, 0, 6);

		// draw to backbuffer (final pass)
		// -----

		// set render states
		glDisable(GL_DEPTH_TEST);
		glDepthMask(GL_TRUE); // enable depth writes so glClear won't ignore clearing the depth buffer
		glDisable(GL_BLEND);

		// bind backbuffer
		glBindFramebuffer(GL_FRAMEBUFFER, 0);
		glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);

		// use screen shader
		screenShader.use();

		// draw final screen quad
		glActiveTexture(GL_TEXTURE0);
		glBindTexture(GL_TEXTURE_2D, opaqueTexture);
		glBindVertexArray(quadVAO);
		glDrawArrays(GL_TRIANGLES, 0, 6);

		// glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
		// -------------------------------------------------------------------------------
		glfwSwapBuffers(window);
		glfwPollEvents();
	}

	// optional: de-allocate all resources once they've outlived their purpose:
	// ------------------------------------------------------------------------
	glDeleteVertexArrays(1, &quadVAO);
	glDeleteBuffers(1, &quadVBO);
	glDeleteTextures(1, &opaqueTexture);
	glDeleteTextures(1, &depthTexture);
	glDeleteTextures(1, &accumTexture);
	glDeleteTextures(1, &revealTexture);
	glDeleteFramebuffers(1, &opaqueFBO);
	glDeleteFramebuffers(1, &transparentFBO);

	glfwTerminate();

	return EXIT_SUCCESS;
}

// glfw: whenever the window size changed (by OS or user resize) this callback function executes
// ---------------------------------------------------------------------------------------------
void framebuffer_size_callback(GLFWwindow* window, int width, int height)
{
	// make sure the viewport matches the new window dimensions; note that width and 
	// height will be significantly larger than specified on retina displays.
	glViewport(0, 0, width, height);
}

// glfw: whenever the mouse moves, this callback is called
// -------------------------------------------------------
void mouse_callback(GLFWwindow* window, double xpos, double ypos)
{
	if (firstMouse)
	{
		lastX = xpos;
		lastY = ypos;
		firstMouse = false;
	}

	float xoffset = xpos - lastX;
	float yoffset = lastY - ypos; // reversed since y-coordinates go from bottom to top

	lastX = xpos;
	lastY = ypos;

	camera.ProcessMouseMovement(xoffset, yoffset);
}

// glfw: whenever the mouse scroll wheel scrolls, this callback is called
// ----------------------------------------------------------------------
void scroll_callback(GLFWwindow* window, double xoffset, double yoffset)
{
	camera.ProcessMouseScroll(yoffset);
}

// process all input: query GLFW whether relevant keys are pressed/released this frame and react accordingly
// ---------------------------------------------------------------------------------------------------------
void process_input(GLFWwindow *window)
{
	if (glfwGetKey(window, GLFW_KEY_ESCAPE) == GLFW_PRESS)
		glfwSetWindowShouldClose(window, true);

	if (glfwGetKey(window, GLFW_KEY_W) == GLFW_PRESS)
		camera.ProcessKeyboard(FORWARD, deltaTime);
	if (glfwGetKey(window, GLFW_KEY_S) == GLFW_PRESS)
		camera.ProcessKeyboard(BACKWARD, deltaTime);
	if (glfwGetKey(window, GLFW_KEY_A) == GLFW_PRESS)
		camera.ProcessKeyboard(LEFT, deltaTime);
	if (glfwGetKey(window, GLFW_KEY_D) == GLFW_PRESS)
		camera.ProcessKeyboard(RIGHT, deltaTime);
}

// generate a model matrix
// ---------------------------------------------------------------------------------------------------------
glm::mat4 calculate_model_matrix(const glm::vec3& position, const glm::vec3& rotation, const glm::vec3& scale)
{
	glm::mat4 trans = glm::mat4(1.0f);

	trans = glm::translate(trans, position);
	trans = glm::rotate(trans, glm::radians(rotation.x), glm::vec3(1.0, 0.0, 0.0));
	trans = glm::rotate(trans, glm::radians(rotation.y), glm::vec3(0.0, 1.0, 0.0));
	trans = glm::rotate(trans, glm::radians(rotation.z), glm::vec3(0.0, 0.0, 1.0));
	trans = glm::scale(trans, scale);

	return trans;
}