#include "stdio.h"
#include "string.h"

#include "glfw3.h"

#include "windows.h"

GLFWwindow* window = 0;

//frame counter vars
static unsigned int frame_count = 0;
static int current_fps = 0;
static double start_time = 0;

//vars for sleep calculations
static double target_frame_rate = 60;
static double frame_start = 0;

void calc_frame_rate()
{
	frame_count++;

	double elapsed = (glfwGetTime() - start_time);

	if (elapsed > 1)
	{
		current_fps = frame_count;
		start_time = glfwGetTime();
		frame_count = 0;
	}
}

void calc_sleep()
{
	double wait_time = 1.0 / (target_frame_rate);
	double curr_frame_time = glfwGetTime() - frame_start;
	double dur = 1000.0 * ( wait_time - curr_frame_time ) + 0.5;
	int durDW = (int)dur;
	if( durDW > 0 ) // ensures that we don't have a dur > 0.0 which converts to a durDW of 0.
	{
		Sleep( (DWORD) durDW  );
	}

	double frame_end = glfwGetTime();
	frame_start = frame_end;
}

int main(int argc, char* args[])
{
	glfwInit();
	window = glfwCreateWindow(640, 480, "", 0, 0);
	glfwMakeContextCurrent(window);
	glfwSwapInterval(0);
	glfwWindowHint(GLFW_RESIZABLE, 0);

	while(!glfwWindowShouldClose(window))
	{
		calc_frame_rate();

        	char str[64] = {};
        	sprintf(str, "%i", current_fps);
		glfwSetWindowTitle(window, str);

        	glfwSwapBuffers(window);

		calc_sleep();
		glfwPollEvents();
	}

	return 0;
}