#include <stdio.h>
#include <GL/glew.h>
#define GLFW_DLL
#include <GLFW/glfw3.h>

#define eprint(fmt, ...) fprintf(stderr, "ERROR: " fmt  "\n" #__VA_ARGS__)

const char *vertex_shader =
	"#version 330 core\n"
	"in vec3 vp;\n"
	"void main() {\n"
	"  gl_Position = vec4(vp, 1.0);\n"
	"}\n";

const char *fragment_shader =
	"#version 330 core\n"
	"out vec4 fragColor;\n"
	"void main() {\n"
	"  fragColor = vec4(0.5, 0.0, 0.5, 1.0);\n"
	"}\n";

int main() {
	if (!glfwInit()) {
		eprint("Could not start glfw");
		return -1;
	}

	glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
	glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 2);
	glfwWindowHint(GLFW_OPENGL_FORWARD_COMPAT, GL_TRUE);
	glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

	GLFWwindow *window = glfwCreateWindow(640, 480, "Hello triangle", NULL, NULL);
	if (!window) {
		eprint("Could not open window with glfw");
		glfwTerminate();
		return -1;
	}
	glfwMakeContextCurrent(window);

	glewExperimental = GL_TRUE;
	glewInit();

	printf("Renderer: %s\n", glGetString(GL_RENDERER));
	printf("OpenGL version supported: %s\n", glGetString(GL_VERSION));

	glEnable(GL_DEPTH_TEST);
	glDepthFunc(GL_LESS);

	float points[] = {
		 0.0f,  0.5f, 0.0f,
		 0.5f, -0.5f, 0.0f,
		-0.5f, -0.5f, 0.0f,
	};

	GLuint vbo = 0;
	glGenBuffers(1, &vbo);
	glBindBuffer(GL_ARRAY_BUFFER, vbo);
	glBufferData(GL_ARRAY_BUFFER, 9 * sizeof(float), points, GL_STATIC_DRAW);

	GLuint vao = 0;
	glGenVertexArrays(1, &vao);
	glBindVertexArray(vao);
	glEnableVertexAttribArray(0);
	glBindBuffer(GL_ARRAY_BUFFER, vbo);
	glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, NULL);

	GLuint vs = glCreateShader(GL_VERTEX_SHADER);
	glShaderSource(vs, 1, &vertex_shader, NULL);
	glCompileShader(vs);

	GLuint fs = glCreateShader(GL_FRAGMENT_SHADER);
	glShaderSource(fs, 1, &fragment_shader, NULL);
	glCompileShader(fs);

	GLuint shader_program = glCreateProgram();
	glAttachShader(shader_program, fs);
	glAttachShader(shader_program, vs);
	glLinkProgram(shader_program);

	while (!glfwWindowShouldClose(window)) {
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		glUseProgram(shader_program);
		glBindVertexArray(vao);
		glDrawArrays(GL_TRIANGLES, 0, 3);
		glfwPollEvents();
		glfwSwapBuffers(window);
	}


	glfwTerminate();
	return 0;
}