#include <stdio.h> 
#include <glut.h> 
  
template <typename T>
struct ListElement {
	T value;
	ListElement<T> *next;

	ListElement(T val){
		value = val;
		next = NULL;
	}

};

template <typename T>
struct List {
	ListElement<T> *first;
	ListElement<T> *current;

	int length = 0;

	List(ListElement<T> *f = NULL){
		first = f;
		current = NULL;
	}

	List *push(T val){
		if(first == NULL){
			first = new ListElement<T>(val);
			current = first;
		} else {
			ListElement<T> *curr = first;
			while(curr->next) curr = curr->next;
			curr->next = new ListElement<T>(val);
		}
		length++;

		return this;
	}

	List *next(){
		current = current->next;
		return this;
	}

	bool nextExists(){
		return current->next != NULL;
	}
};

//int pos0X = 100, pos0Y = 300, repeat = 5; 
struct Dot { 
    int x, y; 
  
    Dot(int _x, int _y){ 
        x = _x; 
        y = _y; 
    } 
}; 
  
List<Dot *> *dots = new List<Dot *>(); 
  
void display(){ 
    //if(dots->length < 2 || dots->length % 2 != 0) return; 
  
    glClear(GL_COLOR_BUFFER_BIT); 
    glPushMatrix(); 
  
    glColor3f(1.0, 1.0, 1.0); 
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE); 
  
    if(dots->length > 2 && dots->length % 2 == 0){ 
        printf("Draw!!!\n"); 
  
        glBegin(GL_POLYGON); 
  
        ListElement<Dot *> *curr = dots->first; 
        Dot *d1, *d2; 
       
  
        glVertex2f(curr->value->x, curr->value->y); 
        curr = curr->next; 
        glVertex2f(curr->value->x, curr->value->y); 
        curr = curr->next; 
  
        while(curr){ 
            d1 = curr->value; 
            curr = curr->next; 
            d2 = curr->value; 
            curr = curr->next; 
  
            glVertex2f(d1->x, d1->y); 
            glVertex2f(d2->x, d2->y); 
  
            glEnd(); 
            glBegin(GL_POLYGON); 
  
            glVertex2f(d1->x, d1->y); 
            glVertex2f(d2->x, d2->y); 
  
        
        } 
  
        glEnd(); 
    } 
  
      glPopMatrix(); 
    glutSwapBuffers(); 
} 
  
void onClick(int button, int state, int x, int y){ 
    if(state != 0 || button != 0) return;  
  
    dots->push(new Dot(x, y)); 
    printf("click: %d %d %d\n", x, y, dots->length); 
    if(dots->length > 2 && dots->length % 2 == 0) display(); 
} 
  
void init(){ 
    glClearColor(0.0, 0.0, 0.0, 0.0); 
    glShadeModel(GL_FLAT); 
} 
  
void reshape(int w, int h){ 
    glViewport(0, 0, (GLsizei) w, (GLsizei) h); 
    glMatrixMode(GL_PROJECTION); 
    glLoadIdentity(); 
    glOrtho(0, 800, 600, 0, -1.0, 1.0); 
    glMatrixMode(GL_MODELVIEW); 
    glLoadIdentity(); 
} 
  
int main(int argc, char** argv){ 
    glutInit(&argc, argv); 
    glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB); 
  
    glutInitWindowSize(800, 600);  
    glutInitWindowPosition(100, 100); 
  
    glutCreateWindow("Lab 3 :: Task 2"); 
  
    init(); 
  
    glutDisplayFunc(display);  
    glutReshapeFunc(reshape); 
    glutMouseFunc(onClick); 
  
    glutMainLoop(); 
  
    return 0; 
}