/*****************************************************************
 *Linked list with a notion of "current node." The current node
 *can be changed to the next node with then method goToNext. At
 *any time after iteration is initialized, one node is the current
 *node, until iteration has moved beyond the end of the list.
 *****************************************************************/
public class StringLinkedListWithIterator
{
    private ListNode head;
    private ListNode current;
    private ListNode previous;

    public StringLinkedListWithIterator()
    {
        head = null;
        current = null;
        previous = null;
    }

    /*****************************************
     *Returns the number of nodes in the list.
     *****************************************/
    public int length()

    {
        int count = 0;
        ListNode position = head;
        while (position != null)
        {
            count++;
            position = position.link;
        }
        return count;
    }

    public void addANodeToStart(String addData)
    {
        head = new ListNode(addData, head);
        if (current == head.link && current != null)
        //if current is at old start node
            previous = head;
    }

    public boolean onList(String target)
    {
         return (Find(target) != null);
    }

    /********************************************************************
     *Finds the first node containing the target data, and returns a
     *reference to that node. If key is not in the list, null is returned.
     ********************************************************************/
    private ListNode Find(String target)
    {
        ListNode position;
        position = head;
        String dataAtPosition;
        while (position != null)
        {
            dataAtPosition = position.data;
            if (dataAtPosition.equals(target))
                return position;
            position = position.link;
        }
        return null;
    }

     public void showList()
    {
        ListNode position;
        position = head;
        ListNode dataAtPosition;
        while (position != null)
        {
            System.out.println(position.data);
            position = position.link;
        }
    }

    public String[] arrayCopy()
    {
        String[] a = new String[length()];

        ListNode position;
        position = head;
        int i = 0;
        while (position != null)
        {
            a[i] = position.data;
            i++;
            position = position.link;
        }

        return a;
    }

    public void resetIteration()
    {
        current = head;
        previous = null;
    }

    public void goToNext()
    {
        if (current != null)
        {
            previous = current;
            current = current.link;
        }
        else if (head != null)
        {
            System.out.println(
               "Iterated too many times or uninitialized iteration.");
            System.exit(0);
        }
        else
        {
            System.out.println("Iterating with an empty list");
            System.exit(0);
      }
    }

    public boolean moreToIterate()
    {
        return (current != null);
    }

    public String getDataAtCurrent()
    {
        if (current != null)
            return (current.data);
        else
        {
            System.out.println(
                    "Getting data when current is not at any node.");
            System.exit(0);
        }
        return null;//to keep compiler happy
   }

   public void resetDataAtCurrent(String newData)
   {
       if (current != null)
       {
           current.data = newData;
       }
        else
        {
            System.out.println(
                 "Setting data when current is not at any node.");
            System.exit(0);
        }
    }

    /**************************************************************
     *Inserts node with newData after the current node. The current
     *node is the same after invocation as it is before invocation.
     *Should not be used with an empty list. Should not be
     *used when the current node has iterated past entire list.
     **************************************************************/
    public void insertNodeAfterCurrent(String newData)
    {
        ListNode newNode = new ListNode();
        newNode.data = newData;
        if (current != null)
        {
            newNode.link = current.link;
            current.link = newNode;
        }
        else if (head != null)
        {
            System.out.println(
                        "Inserting when iterator is past all "
                      + "nodes or uninitialized iterator.");
            System.exit(0);
        }
        else
        {
            System.out.println(
                  "Using insertNodeAfterCurrent with empty list");
            System.exit(0);
      }
    }

    /***********************************************
     *Deletes current node. After the invocation,
     *the current node is the node after the
     *deleted node or null if there is no next node.
     ***********************************************/
    public void deleteCurrentNode()
    {
        if ((current != null) && (previous != null))
        {
            previous.link = current.link;
            current = current.link;
        }
        else if( (current != null) && (previous == null))
        {//At head node
            head = current.link;
            current = head;
        }
        else //current == null
        {
            System.out.println(
             "Deleting with uninitialized current or an empty list");
            System.exit(0);
        }
    }

    private class ListNode
    {
        private String data;
        private ListNode link;

        public ListNode()
        {
            link = null;
            data = null;
        }

        public ListNode(String newData, ListNode linkValue)
        {
            data = newData;
            link = linkValue;
        }
    }
}