package lab.util;

import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * An iterator over <code>Node</code>-based linked sequences.
 *
 * @param <E> the element type held by a node
 */
public class NodeIterator<E> implements Iterator<Node<E>> {

  private Node<E> prev;
  private Node<E> curr;
  
  /**
   * Create an iterator that starts iterating at the node
   * <code>head</code>
   * 
   * @param head the node at which to start iterating
   */
  public NodeIterator(Node<E> head) {
    this.curr = head;
    this.prev = null;
  }
  
  /**
   * Returns true if this iterator has another node in the sequence.
   * 
   * @return true if and only if this iterator has another node
   * @see java.util.Iterator#hasNext()
   */
  @Override
  public boolean hasNext() {
    return curr != null;
  }

  /**
   * Returns the next node in the sequence.
   * 
   * @return the next node in the sequence
   * @throws NoSuchElementException if no more nodes are available
   * @see java.util.Iterator#next()
   */
  @Override
  public Node<E> next() {
    if (this.hasNext()) {
      this.prev = this.curr;
      this.curr = this.curr.getNext();
    }
    else {
      throw new NoSuchElementException();
    }
    return this.prev;
  }

  /**
   * The remove operation is not supported by this implementation of Iterator.
   * 
   * @throws UnsupportedOperationException if this method is invoked
   * @see java.util.Iterator#remove()
   */
  @Override
  public void remove() {
    throw new UnsupportedOperationException();
  }

}