package class5_2_CircularQueue_021;

// TODO: Untested code!

public class CircularQueue<E> implements Queue<E> {
    private final int MAX_SIZE = 6; // Smaller value makes testing easier

    int indFront = 0; // The "front of the line" i.e. first items to come off
    int indRear = -1; // The "back of the line" i.e. most recently arrived items.

    E[] array = (E[]) new Object[MAX_SIZE];

    @Override
    public E poll() {
        if(isEmpty()) {
            return null;
        }

        E result = array[indFront];
        indFront++;

        if(indFront == indRear + 1) {
            // Queue is again empty!
            indFront = 0;
            indRear = -1;
        }
        else if(indFront >= array.length) {
            indFront = 0;
        }

        return result;
    }

    @Override
    public boolean offer(E e) {
        if(isFull()) {
            return false;
        }

        indRear++;
        if(indRear >= array.length) {
            indRear = 0;
        }

        array[indRear] = e;

        return true;
    }

    @Override
    public E peek() {
        if(isEmpty()) {
            return null;
        }

        return array[indFront];
    }

    @Override
    public boolean isEmpty() {
        return (indRear < 0);
    }

    /**
     * Returns true if no more elements can be added to the array.
     * @return true if full
     */
    private boolean isFull() {
        return ((indRear+1)%array.length == indFront);
    }
}