#include <GL/glut.h>
#include <stdio.h>
#include <math.h>

static int year = 0, month = 0;
static double pi = 3.1415926;

void display(void)
{
  glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

  glMatrixMode(GL_MODELVIEW);

  glLoadIdentity();

  glColor3f (1.0, 0.0, 0.0);
  glutWireSphere(1.0, 50, 50);        /* draw sun */

  glLoadIdentity();

  glRotatef((GLfloat) year, 0.0, 1.0, 0.0);
  glTranslatef (2.0, 0.0, 0.0);
  glColor3f(0.0,0.0,1.0);
  glutWireSphere(0.2, 20, 20);        /* draw earth */

  glLoadIdentity();

  glTranslatef(2.0*cos(year*2*pi/360),0, 2.0*sin(-year*2*pi/360));
  glRotatef((GLfloat) month, 0.0, 1.0, 0.0);
  glTranslatef(-2.0*cos(year*2*pi/360),0, -2.0*sin(-year*2*pi/360));

  glRotatef((GLfloat) year, 0.0, 1.0, 0.0);
  glTranslatef (2.5, 0.0, 0.0);
  glColor3f(0.0,1.0,0.0);
  glutWireSphere(0.1, 10, 10);        /* draw moon */

  glFlush();
  glutSwapBuffers();
}

void myReshape(GLsizei w, GLsizei h)
{
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluPerspective(90.0, (GLfloat) w/(GLfloat) h, 1.0, 40.0);
  gluLookAt(0,2,2.5, 0,0,0, 0,1,0);
}

void keyboard(unsigned char key, int x, int y){
  switch(key)
    {case 'd':
	year = (year + 1) % 360;
	month = (month + 5) % 360;
	break;
    }
}

int main(int argc, char** argv)
{
  glutInit(&argc, argv);
  glutInitDisplayMode (GLUT_DOUBLE | GLUT_RGBA);
  glutInitWindowPosition(0, 0);
  glutInitWindowSize(800, 800);
  glutCreateWindow("A solar system");

  glutReshapeFunc(myReshape);
  glutDisplayFunc(display);
  glutIdleFunc(display);
  glutKeyboardFunc(keyboard);
  glutMainLoop();
}