import java.util.NoSuchElementException;

/**
 * A generic LinkedList implementation.
 * 
 * @author gtowell Created: Sep 2019 Modified: Jan 2020 Modified: Nov 2020
 */
public class LinkedList<T> implements LinkedListInterface<T> {

    /**
     * The node class. Each element in the linked list is an instance of Node
     */
    private class Node<V> {
        /** The data item in the node. */
        public V data;
        /** The next item in the linked list */
        public Node<V> next;

        /**
         * Node constructor. Takes a data item and another node
         */
        public Node(V data, Node<V> next) {
            this.data = data;
            this.next = next;
        }
    }

    /** The start, first element, of the linked list */
    private Node<T> head = null;

    /** THe last element in the linked list */
    private Node<T> tail = null;

    /** The number of items in the linked list */
    private int size = 0;

    /**
     * The number of items in the linked list
     * 
     * @return the number of items in the linked list
     */
    @Override
    public int size() {
        return size;
    }

    /**
     * Returns true iff the linked list has no elements
     * 
     * @return true iff the linked list has no elements
     */
    @Override
    public boolean isEmpty() {
        return size == 0;
    }

    /**
     * Get the first element in the linked list
     * 
     * @return the first element in the linked list
     * @throws NoSuchElementException is the list is empty
     */
    @Override
    public T first() throws NoSuchElementException {
        if (head == null)
            throw new NoSuchElementException("The list is empty");
        return head.data;
    }

    /**
     * The last element in the linked list
     * 
     * @return the last elment
     * @throws NoSuchElementException if the linked list is empty
     */
    @Override
    public T last() throws NoSuchElementException {
        if (head == null)
            throw new NoSuchElementException("The list is empty");
        return tail.data;
    }

    /**
     * Add an element to the end of the list
     * 
     * @param c the element to be added
     */
    @Override
    public void addLast(T c) {
        Node<T> newest = new Node<>(c, null);
        if (isEmpty()) {
            head = newest;
        } else {
            tail.next = newest;
        }
        tail = newest;
        size++;
    }

    /**
     * Add an element at the front of the list
     * 
     * @param c the element to be added
     */
    @Override
    public void addFirst(T c) {
        Node<T> newest = new Node<>(c, null);
        if (isEmpty()) {
            head = newest;
            tail = newest;
        } else {
            newest.next = head;
        }
        head = newest;
        size++;
    }

    /**
     * Remove the first element from the list
     * 
     * @return the first element, or null if the list is empty
     */
    @Override
    public T removeFirst() {
        if (head == null)
            return null;
        T rtn = head.data;
        head = head.next;
        if (head == null)
            tail = null;
        return rtn;
    }

    /**
     * Remove the last from the list
     * 
     * @return the last element, or null if the list is empty
     */
    @Override
    public T removeLast() {
        if (head == null)
            return null;
        if (head == tail) {
            head = null;
            T rtn = tail.data;
            size = 0;
            tail = null;
            return rtn;
        }
        // start at front and get to the node prior to the last
        Node<T> curr = head;
        while (curr.next != tail) {
            curr = curr.next;
        }
        T rtn = tail.data;
        tail = curr;
        tail.next = null;
        size--;
        return rtn;
    }

    /**
     * Remove the specified element from the list
     * 
     * @param r the element to be removed
     * @return the removed element, or null is the element was not in the list
     */
    @Override
    public boolean remove(T r) {
        return false;
    }

    public String toString() {
        StringBuffer s = new StringBuffer();
        for (Node<T> n = head; n != null; n = n.next) {
            s.append(n.data.toString());
            if (n != tail) {
                s.append("\n");
            }
        }
        return s.toString();
    }

    public static void main(String[] args) {
    }
}