import cs101.terminal.*;

public class ListOfInts {
   ListItem marker; // the current item is the one after the marker
   ListItem head;   // always refers to the dummy
   ListItem rear;   // always refers to the last item in the list
 
   ListOfInts() {
      head = rear = marker = new ListItem(0, null);  // create dummy
   }

   public boolean isEmpty() {
      return (head.next == null);  // alternatively, (head == rear)
   }

   public ListOfInts prepend(int n) {
      head.next = new ListItem(n, head.next);
      if (head == rear)  // check if this is also the last item
         rear = head.next;
      return this;
   }

   public ListOfInts append(int n) {
      rear.next = new ListItem(n, null);
      rear = rear.next;
      return this;
   }

   public boolean atEnd() {
      return (marker.next == null);
   }

   public void reset() {
      marker = head;
   }

   public ListOfInts next() {
      if (!atEnd())
         marker = marker.next;
      return this;
   }

   public int getItem() {  // gets current item
      if (atEnd())
         Terminal.println("Error: Tried to get item past end of list!");
      else
         return marker.next.number;
   }

   public void setItem(int n) {  // replaces value of current item
      if (atEnd())
         Terminal.println("Error: Tried to set item past end of list!");
      else
         marker.next.number = n;
   }

   public void insert(int n) {  // inserts n just before the current item, and
                                // the new item n becomes the current item
      if (atEnd())  // appends the item if marker is at the end
         append(n);
      else
         marker.next = new ListItem(n, marker.next);
   }

   public int delete() {  // deletes the current item
      if (atEnd()) {
         Terminal.println("Error: Tried to delete item past end of list!");
         return 0;
      }
      else {
         result = marker.next.number;
         if (marker.next == rear)
           rear = marker;
         marker.next = marker.next.next;
         return result;
      }
   }

   public String toString() {
      if (isEmpty())
         return "( )";
      else
         return "(" + head.next + " )";
   }
}

class ListItem {
   public int number;
   public ListItem next;

   ListItem(int number, ListItem next) {
      this.number = number;
      this.next = next;
   }

   public String toString() {
      if (this.next == null)
         return (" " + number);
      else
         return (" " + number + this.next);
   }
}