import CITS2200.*;
public class DequeCyclic<E> implements Deque<E>
{
    
    private E[] items; 
    private int first; //holds index of first item
    private int last; //holds index of last item
    private int size; //size of Queue
    @SuppressWarnings("unchecked")
    public DequeCyclic(int s) {
        E[] items = (E[]) new Object[s];
        this.items = items;
        first = 0;
        last = 0;
        size = s - 1; //sets size to max index
    }
    
    public boolean isEmpty() {
        return items[first] == null; //if the first item in a Queue is null, the Queue is empty
    }
    public boolean isFull() {
        return first == last + 1;
    }
    public void pushLeft(E c) throws Overflow {
        if(!isFull()) 
        {
            if(isEmpty()){items[first] = c;} //if adding to an empty Queue you don't need to change the index
            else {
                first--; 
                if(first < 0) {first = size;} //if it goes neg, change to max index
                items[first] = c;
            }
        }
        else {throw new Overflow("Queue is Full");}
    }
    public void pushRight(E c) throws Overflow {
        if(!isFull()) 
        {
            if(isEmpty()){items[last] = c;}
            else{
                last = (last + 1) % items.length; //prevents it from going over the max index
                items[last] = c;
            }
        }
        else {throw new Overflow("Queue is Full");}
    }
    public E peekLeft() throws Underflow {
        if(!isEmpty()) {return items[first];}
        else {throw new Underflow("Queue is Empty");}
    }
    public E peekRight() throws Underflow {
        if(!isEmpty()) {return items[last];}
        else {throw new Underflow("Queue is Empty");}
    }
    public E popLeft() throws Underflow {
        if(!isEmpty()) {
            E RET = items[first];
            items[first] = null;
            if(last != first) {first = (first + 1) % items.length;} //doesn't change index if Queue will be empty, otherwise go as normal.
            return RET;
        }
        else {throw new Underflow("Queue is Empty");}
    }
    public E popRight() throws Underflow {
        if(!isEmpty()) {
            E RET = items[last];
            items[last] = null;
            if(last != first) { 
            last--;
            if(last < 0) last = size;
        } //doesn't change index if Queue will be empty, otherwise go as normal.
            return RET;
        }
        else {throw new Underflow("Queue is Empty");}
    }
}