/* Simplified OpenGL 4.5 demo
 * Seth Long, Fall 2020
 * This is a *very* short demo which displays a triangle
 * Many of these functions can fail, and return error values
 * I doubt it can be done much shorter without leaving vertices in only main memory or some such
 * If moving to C++, use GLM instead of cglm
 */

#include<stdio.h>
#include<stdlib.h>
#include<fcntl.h>
#include<unistd.h>
#include<GL/glew.h>
#include<GLFW/glfw3.h>
#include<glm/glm.hpp>
#include<glm/gtc/matrix_transform.hpp>
#include<glm/gtc/type_ptr.hpp>

using namespace glm;

const float height = 1600;
const float width = 2560/2;

int main(int argc, char ** argv){
	glfwInit();
	GLFWwindow* window = glfwCreateWindow(width, height, "Simple OpenGL 4.0+ Demo", 0, 0);
	glfwMakeContextCurrent(window);
	glewInit();

	// Initialization part
	float vertices[] = {0, 1, 0, -0.5, 0, 0, 0.5, 0, 0};
	unsigned int vbuf;
	glGenBuffers(1, &vbuf);
	glBindBuffer(GL_SHADER_STORAGE_BUFFER, vbuf);
	glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);

	float colors[] = {1, 0, 0, 1, 0, 0, 0, 0.5, 0};
	unsigned int cbuf;
	glGenBuffers(1, &cbuf);
	glBindBuffer(GL_SHADER_STORAGE_BUFFER, cbuf);
	glBufferData(GL_SHADER_STORAGE_BUFFER, sizeof(colors), colors, GL_STATIC_DRAW);

	int fd = open("vertex_shader.glsl", O_RDONLY);
	char *source = (char*)malloc(2048);
	size_t readlen = read(fd, source, 2048);
	if(2048 == readlen)
		printf("Warning:  vertex shader is probably too long for this read routine\n");
	source[readlen] = 0;
	puts(source);
	close(fd);
	unsigned int vs_reference = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vs_reference, 1, (const char**)&source, 0);
	glCompileShader(vs_reference);
	
	fd = open("fragment_shader.glsl", O_RDONLY);
	readlen = read(fd, source, 2048);
	source[readlen] = 0;
	puts(source);
	close(fd);
	unsigned int fs_reference = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fs_reference, 1, (const char**)&source, 0);
	glCompileShader(fs_reference);
	free(source);

	unsigned int program = glCreateProgram();
	glAttachShader(program, vs_reference);
	glAttachShader(program, fs_reference);
	glLinkProgram(program);
	
	unsigned int v_attrib = glGetAttribLocation(program, "in_vertex");
	unsigned int c_attrib = glGetAttribLocation(program, "in_color");
	unsigned int mvp_uniform = glGetUniformLocation(program, "mvp");

	int count = 0;

	glUseProgram(program);

	glEnableVertexAttribArray(v_attrib);
	glBindBuffer(GL_ARRAY_BUFFER, vbuf);
	glVertexAttribPointer(v_attrib, 3, GL_FLOAT, GL_FALSE, 0, 0);

	glEnableVertexAttribArray(c_attrib);
	glBindBuffer(GL_ARRAY_BUFFER, cbuf);
	glVertexAttribPointer(c_attrib, 3, GL_FLOAT, GL_FALSE, 0, 0);

//	glEnable(GL_DEPTH_TEST);
	while(!glfwWindowShouldClose(window)){
		count++;
		glfwPollEvents();
		glClearColor(1.0, 1.0, 1.0, 1.0);
		glClear(GL_COLOR_BUFFER_BIT);

		mat4 model = rotate(mat4(1.0), count / 100.0f, vec3(0, 1, 0));

		mat4 view = lookAt(((vec3){0.0f, 0.0f, 9.0f}), vec3(0, 0, -1), vec3(0, 1, 0));
		mat4 projection = perspective(45.0f, width/height, 0.1f, 1000.0f);
		mat4 mvp = projection * view * model; 
		glUniformMatrix4fv(mvp_uniform, 1, 0, value_ptr(mvp));

		glDrawArraysInstanced(GL_TRIANGLES, 0, 3, 10);

		glfwSwapBuffers(window);
//		usleep(10000);
	}

	glDeleteProgram(program);
	glfwDestroyWindow(window);
	glfwTerminate();
}