/*
 * Draw a sun and a planet in orbit around the sun.
 */
#include <stdlib.h>
#include <GL/glut.h>

static int day     = 0,
           year    = 0,
           month   = 0;

void init(void)
{
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glShadeModel(GL_FLAT);
}

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(1.0, 1.0, 1.0);

    // Draw sun
    glPushMatrix();
        glRotatef(90.0, 1.0, 0.0, 0.0); // Put both poles on Y axis.
        glutWireSphere(1.0, 20, 16);
    glPopMatrix();

    // Move to planet1 origin
    glPushMatrix();
            
        glRotatef((GLfloat) year, 0.0, 1.0, 0.0);
        glTranslatef(5.0, 0.0, 0.0);

        // Draw planet
        glPushMatrix();
            glRotatef(20.0, 1.0, 0.0, 0.0); // Tilt
            glRotatef((GLfloat) day, 0.0, 1.0, 0.0);

            glRotatef(90.0, 1.0, 0.0, 0.0); // Put both poles on Y axis.
            glutWireSphere(0.2, 10, 8);
        glPopMatrix();

        // Move to moon1 origin and draw it.
        glPushMatrix();
            glRotatef((GLfloat) month, 0.0, 1.0, 0.0);
            glTranslatef(1.0, 0.0, 0.0);

            glRotatef(90.0, 1.0, 0.0, 0.0); // Put poles on Y axis.
            glutWireSphere(0.1, 10, 8);
        glPopMatrix();

        // Move to moon2 origin and draw it.
        glPushMatrix();
            glRotatef((GLfloat) month*2, 0.0, 1.0, 0.0);
            glTranslatef(0.6, 0.0, 0.0);

            glRotatef(90.0, 1.0, 0.0, 0.0); // Put poles on Y axis.
            glutWireSphere(0.05, 10, 8);
        glPopMatrix();

    glPopMatrix();

    // Move to planet2 origin and draw it.
    glPushMatrix();
        
        glRotatef((GLfloat) year * 2.0, 0.0, 1.0, 0.0);
        glTranslatef(2.5, 0.0, 0.0);
        
        glRotatef(90.0, 1.0, 0.0, 0.0); // Put both poles on Y axis.
        glutWireSphere(0.15, 10, 8);

    glPopMatrix();
        

    glutSwapBuffers();
}

void reshape(int w, int h)
{
    glViewport(0, 0, (GLsizei) w, (GLsizei) h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60.0, (GLfloat) w / (GLfloat) h, 1.0, 20.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(8.0, 2.0, 8.0,  // Eye
              0.0, 0.0, 0.0,  // Center
              0.0, 1.0, 0.0); // Up
}

void keyboard(unsigned char key, int x, int y)
{
    switch (key) {
        case 'd':
            day = (day + 10) % 360;
            glutPostRedisplay();
            break;

        case 'D':
            day = (day - 10) % 360;
            glutPostRedisplay();
            break;

        case 'y':
            year = (year + 5) % 360;
            glutPostRedisplay();
            break;

        case 'Y':
            year = (year - 5) % 360;
            glutPostRedisplay();
            break;

        case 'm':
            month = (month + 5) % 360;
            glutPostRedisplay();
            break;

        case 'M':
            month = (month - 5) % 360;
            glutPostRedisplay();
            break;

        case 'a':
            day = (day + 10) % 360;
            year = (year + 5) % 360;
            month = (month + 5) % 360;
            glutPostRedisplay();
            break;

        case 'A':
            day = (day - 10) % 360;
            year = (year - 5) % 360;
            month = (month - 5) % 360;
            glutPostRedisplay();
            break;

        case 27:
            exit(0);

        default:
            break;
    }
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
    glutInitWindowSize(500, 500);
    glutInitWindowPosition(100, 100);
    glutCreateWindow(argv[0]);
    init();
    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutKeyboardFunc(keyboard);
    glutMainLoop();
    return 0;
}