public class ArrayQueue<T> implements QueueADT<T>, Serializable {

    public static final int DEFAULT_CAPACITY = 100;
    private int front;
    private int count;
    private T[] queue;

    public ArrayQueue() {
        this(DEFAULT_CAPACITY);
    }

    public ArrayQueue(int initialCapacity) {
        queue = (T[])new Object[initialCapacity];
        front = 0;
        count = 0;
    }

    public void enqueue(T element) throws IllegalArgumentException {
        if (element == null) {
            throw new IllegalArgumentException("Null values are npt accepted");
        }
        else if (count >= queue.length) {
            expandCapacity();
            this.enqueue(element);
        }
        else {
            queue[(front + count) % queue.length] = element;
            count++;
        }
    }

    public T dequeue() throws IllegalStateException {
        if (this.isEmpty()) {
            throw new IllegalStateException("Element cannot be dequeued! The queue is empty!");
        }
        T element = queue[front];
        queue[front++] = null;
        count--;
        return element;
    }

    public T first() throws IllegalStateException{
        if (this.isEmpty()) {
            throw new IllegalStateException("There is no first element! The queue is empty!");
        }
        return queue[front];
    }

    public int indexOf(T element) {
        int dequeues = 0;
        for (int i = front; i < this.queue.length; i++) {
            if (queue[i] != null && queue[i].equals(element)) {
                return dequeues;
            }
            dequeues++;
        }
        for (int i = 0; i < front; i++) {
            if (queue[i] != null && queue[i].equals(element)) {
                return dequeues;
            }
            dequeues++;
        }
        return -1;
    }

    public boolean isEmpty() {
        if (this.size() == 0) return true;
        return false;
    }

    public int size() {
        return count;
    }

    public String toString() {
        String result = "";
        for (int i = front; i < queue.length; i++) {
            if (i != front && queue[i] != null) {
                result += ", " + queue[i];
            } else if (queue[i] != null){
                result += queue[i];
            }
        }
        return String.format("{%s}", result);
    }

    public void expandCapacity() {
        T[] newQueue = (T[])(new Object[queue.length * 2]);

        for (int i = 0; i < queue.length; i++) {
            newQueue[i] = queue[i];
        }

        this.queue = newQueue;
    }

    public T[] getQueue() {
        return this.queue;
    }
}