package deque;

/* The Deque interface defines the expected behavior for any
 * Deque, whether it is an ArrayDeque or LinkedListDeque. A
 * Deque is a doubly-ended queue, that allows you to quickly add
 * and remove items from the front and back. */
public interface Deque<T> {
    /**
     * Adds an item of type T to the front of the deque.
     * You can assume that item is never null.
     */
    void addFirst(T item);


    /**
     * Adds an item of type T to the back of the deque.
     * You can assume that item is never null.
     */
    void addLast(T item);

    /**
     * Returns true if deque is empty, false otherwise.
     */
    default boolean isEmpty() {
        return size() == 0;
    }

    /**
     * Returns the number of items in the deque.
     */
    int size();

    /**
     * Prints the items in the deque from first to last, separated by a space.
     * Once all the items have been printed, print out a new line.
     */
    void printDeque();

    /**
     * Removes and returns the item at the front of the deque.
     * If no such item exists, returns null.
     */
    T removeFirst();

    /**
     * Removes and returns the item at the back of the deque.
     * If no such item exists, returns null.
     */
    T removeLast();

    /**
     * Gets the item at the given index,
     * where 0 is the front, 1 is the next item, and so forth.
     * If no such item exists, returns null. Must not alter the deque!
     */
    T get(int index);

    /**
     * Returns whether the parameter o is equal to the Deque.
     * o is considered equal if it is a Deque and contains the same contents
     * (as governed by the generic T’s equals method) in the same order.
     */
    @Override
    default boolean equals(Object o) {
        if (this == o) {
            return true;
        } else if (o == null) {
            return false;
        } else if (!(o instanceof Deque)) {
            return false;
        }

        Deque<T> deqCmp = (Deque<T>) o;
        if (size() != deqCmp.size()) {
            return false;
        }
        for (int index = 0; index <= size() - 1; index++) {
            if (!get(index).equals(deqCmp.get(index))) {
                return false;
            }
        }
        return true;
    }
}