#include <iostream>
#include <glut.h>

float angle = 0.0f;

bool pause = false;

double zoom_in_out_x = 200.0f;
double zoom_in_out_y = 200.0f;
double zoom_in_out_z = 0.0f;

double upvector_x = 1.0f;
double upvector_y = 0.0f;
double upvector_z = 1.0f;

void renderScene(void);
void changeSize(int width, int height);
void processSpecialKeys(int key, int x, int y);
void processNormalKeys(unsigned char key, int x, int y);

int main(int argc, char **argv)
{
    // initialize glut and create window
    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
    glutInitWindowPosition(100, 100);
    glutInitWindowSize(320, 320);
    glutCreateWindow("Solar System");

    // register callback functions
    glutDisplayFunc(renderScene);
    glutReshapeFunc(changeSize);
    glutIdleFunc(renderScene);


    // register keyboard entry
    glutSpecialFunc(processSpecialKeys);
    glutKeyboardFunc(processNormalKeys);

    // enter glut event processing loop
    glutMainLoop();

    return 1;
}

void renderScene(void)
{
    // clear color and depth buffers
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    // reset transformations
    glLoadIdentity();

    // set camera initial position
    gluLookAt(0.0f, zoom_in_out_y, zoom_in_out_z,
              0.0f, 0.0f, 0.0f,
              upvector_x, upvector_y, upvector_z);

    // draw earth
    glPushMatrix();
        glColor3f(0.0, 1.0, 0.0);
        glRotatef(angle, 0.0f, 1.0f, 0.0f);
        glTranslatef(0.0f, 0.0f, 50.0f);
        glutSolidSphere(10, 50, 50);
        //draw moon
        glPushMatrix();
            glColor3f(0.5, 0.5, 0.5);
            glRotatef(angle, 0.0f, 1.0f, 0.0f);
            glTranslatef(0.0f, 0.0f, 20.0f);
            glutSolidSphere(5, 50, 50);
        glPopMatrix();
    glPopMatrix();

    // draw sun
    glPushMatrix();
        glColor3f(1.0f, 1.0f, 0.0f);
        glTranslatef(0.0f, 0.0f, 0.0f);
        glutSolidSphere(20, 50, 50);
    glPopMatrix();

    //draw stars
    for (int i = 1; i <= 5; i++)
    {
        glPushMatrix();
            glColor3f(1.0f, 1.0f, 1.0f);
            glTranslatef(50.0f, 50.0f, 0.0f + i * 10);
            glutSolidSphere(2, 50, 50);
        glPopMatrix();

        glPushMatrix();
            glColor3f(1.0f, 1.0f, 1.0f);
            glTranslatef(-50.0f, 50.0f, 0.0f + i * 10);
            glutSolidSphere(2, 50, 50);
        glPopMatrix();

        glPushMatrix();
        glColor3f(1.0f, 1.0f, 1.0f);
        glTranslatef(50.0f, -50.0f, 0.0f + i * 10);
        glutSolidSphere(2, 50, 50);
        glPopMatrix();

        glPushMatrix();
        glColor3f(1.0f, 1.0f, 1.0f);
        glTranslatef(50.0f, 50.0f, 0.0f - i * 10);
        glutSolidSphere(2, 50, 50);
        glPopMatrix();
    }

    //rotate
    if(pause == false)
        angle += 0.1f;

    glutSwapBuffers();
}

void changeSize(int width, int height)
{

    // prevent division by zero when window is too short
    if (height == 0) height = 1;
    float ratio = 1.0* width / height;

    // use the projection matrix
    glMatrixMode(GL_PROJECTION);

    // reset matrix
    glLoadIdentity();

    // set the viewport to be the entire window
    glViewport(0, 0, width, height);

    // set the correct perspective
    gluPerspective(45, ratio, 1, 1000);

    // Get Back to the Modelview
    glMatrixMode(GL_MODELVIEW);
}

void processNormalKeys(unsigned char key, int x, int y)
{
    switch (key)
    {
        // press esc to exit
        case 27:
            exit(0);break;
        // press space to pause rotation
        case 32:
            pause = !pause; break;
        // press + to zoom in
        case 43:
            zoom_in_out_y -= 5; break;
        // press - to zoom out
        case 45:
            zoom_in_out_y += 5; break;
        default:break;
    }
}

void processSpecialKeys(int key, int x, int y)
{
    switch (key)
    {
        // press left key to rotate camera angle left
        case GLUT_KEY_LEFT:
            upvector_x -= 0.1f;
            upvector_y += 0.1f;
            upvector_z += 0.1f;
            zoom_in_out_x += 20;
            zoom_in_out_z -= 20;
            break;
        // press right key to rotate camera angle right
        case GLUT_KEY_RIGHT:
            upvector_x += 0.1f;
            upvector_y -= 0.1f;
            upvector_z -= 0.1f;
            zoom_in_out_x -= 20;
            zoom_in_out_z += 20;
            break;
        // press up key to rotate camera angle up
        case GLUT_KEY_UP:
            upvector_x += 0.1f;
            upvector_y -= 0.1f;
            upvector_z += 0.1f;
            zoom_in_out_y += 20;
            zoom_in_out_z -= 20;
            break;
        // press down key to rotate camera angle down
        case GLUT_KEY_DOWN:
            upvector_x -= 0.1f;
            upvector_y += 0.1f;
            upvector_z -= 0.1f;
            zoom_in_out_y -= 20;
            zoom_in_out_z += 20;
            break;
        default:break;
    }
}