package lab1_InterfaceStack;

public class MyStackClass implements MyStack, Iterable<Object> {

    private class Element {
        private Object data;
        private Element next;

        public Element(Object data) {
            this.data = data;
            this.next = null;
        }

        public Element(Object _data, Element _next) {
            this.data = _data;
            this.next = _next;
        }

        public Object getData() {
            return this.data;
        }

        public Element getNext() {
            return this.next;
        }
    }

    private Element last_element;
    private int size;

    public MyStackClass() {
        last_element = null;
        size = 0;
    }

    @Override
    public Object pop() {
        if (size == 0)
            return null;
        Object _obj = last_element.getData();
        last_element = last_element.getNext();
        size--;
        return _obj;
    }

    @Override
    public void push(Object o) {
        if (size == 0) {
            last_element = new Element(o);
        }
        else {
            Element elem = new Element(o, last_element);
            last_element = elem;
        }
        size++;
    }

    @Override
    public int size() {
        return size;
    }

    @Override
    public Iterator<Object> iterator() {
        return new Iterator<Object>() {
            private Element current = last_element;

            @Override
            public boolean hasNext() {
                return current.getNext() != null;
            }

            @Override
            public Object next() {
                Object temp = current.getData();
                current = current.getNext();
                return temp;
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException();
            }
        };
    }
}