package wek3;

import wek1.EmptyCollectionException;

public class CircularArrayQueue<T> implements QueueADT<T> {
    private final static int DEFAULT_CAPACITY = 100;
    private int front, rear, count;
    private T[] queue;


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


    public CircularArrayQueue() {
        this(DEFAULT_CAPACITY);
    }


    @Override
    public void enqueue(T element) {
        if (size() == queue.length) {
            expandCapacity();
        }

        queue[rear] = element;
        rear = (rear + 1) % queue.length;

        count++;
    }

    /**
     * Creates a new array to store the contents of this queue with
     * twice the capacity of the old one.
     */
    private void expandCapacity() {
        T[] larger = (T[]) (new Object[queue.length * 2]);

        for (int scan = 0; scan < count; scan++) {
            larger[scan] = queue[front];
            front = (front + 1) % queue.length;
        }

        front = 0;
        rear = count;
        queue = larger;
    }


    @Override
    public T dequeue() throws EmptyCollectionException {
        if (isEmpty()) {
            throw new EmptyCollectionException("queue");
        }

        T result = queue[front];
        queue[rear] = null;
        front = (front + 1) % queue.length;

        count--;

        return result;
    }

    @Override
    public T first() throws EmptyCollectionException {
        if (isEmpty()) {
            throw new EmptyCollectionException("wrong");
        }
        T result = queue[front];
        return result;
    }


    @Override
    public int size() {
        return rear - front;
    }

    @Override
    public boolean isEmpty() {
        if (size() == 0) {
            return true;
        } else {
            return false;
        }
    }

    @Override
    public String toString() {
        int j = front;//从头开始遍历
        String result = "";
        for (int i = 0; i < size(); i++) {//逐渐向后遍历
            result += queue[j] + " ";
            j = (j + 1) % queue.length;//如果到达末端，则索引回0，否则加1继续
        }
        return result;
    }
}