package list.dl;

import java.util.NoSuchElementException;
import list.dl.algo.IAlgoLeft;
import list.dl.algo.IAlgoRight;

/**
* Singleton pattern representing the left end node of a doubly-linked list.
 * @author DXN
 * @version 3.2
 * @since 10/17/00
*/
class LeftEndNode extends ANode
{
   final static LeftEndNode Singleton = new LeftEndNode ();
	private LeftEndNode ()
	{
   }

   Object getFirst (DLList owner)
   // Pre: this node is the left node of owner.
   {
      throw new NoSuchElementException ("LeftEndNode.getLeftFirst: Left end has no data.");
   }

   DLList getLeftRest (DLList owner)
   // Pre: this node is the left node of owner.
   {
      throw new NoSuchElementException ("LeftEndNode.getLeftRest: Left end has no left tail.");
   }

   /**
   * Throws IllegalStateException.  Can never be a the right node of a DLList
   * @param owner
   * @return
   */
   Object getRightFirst (DLList owner)
   {
      throw new IllegalStateException ("Should never call LeftEnd.getRightFirst ()");
   }

   /**
   * Throws IllegalStateException.  Can never be a the right node of a DLList
   * @param owner
   * @return
   */
   DLList getRightRest(DLList owner)
   {
      throw new IllegalStateException ("Should never call LeftEnd.getRightRest ()");
   }

   /**
   * Throws IllegalStateException.
   * @param dllist
   */
   void setLeftOwner (DLList dllist)
   {
      throw new IllegalStateException ("Should never call LeftEnd.setLeftOwner ()");
   }

   /**
   * Does nothing.
   * @param dllist
   */
   void setRightOwner (DLList dllist)
   {
   }

   /**
   <Pre>
   Pre: this node is the left node of owner.
   Post: this node is the left node of owner.getLeftRest ().
   </Pre>
   * @param dat
   */
   void insertLeftFront (Object dat, DLList owner)
   {
      new DataNode (dat, new DLList (), owner);
         /* Old style:
         DLList newList = new DLList ();
         DataNode newNode = new DataNode (dat, newList, owner);
         newList.setRightNode (newNode);
         owner.setLeftNode (newNode);
         */
   }

   Object remLeftFront (DLList owner)
   // Pre: this node is the left node of owner.
   {
      throw new NoSuchElementException ("LeftEndNode.remLeftFront: Left end has no data.");
   }

   /**
   * Throws IllegalStateException.  Can never be a the right node of a DLList
   * @param dat the element to be inserted to the right front of the owner.
   * @param owner the DLList that holds this ANode.
   */
   void insertRightFront (Object dat, DLList owner)
   {
      throw new IllegalStateException ("Should never call LeftEnd.insertRightFront ()");
   }

   /**
   * Throws IllegalStateException.  Can never be a the right node of a DLList
   * @param owner the DLList that holds this ANode.
   * @return
   */
   Object remRightFront (DLList owner)
   {
      throw new IllegalStateException ("Should never call LeftEnd.remRightFront ()");
   }

   /**
   * Throws NoSuchElementException.
   * @param dat
   */
   void setFirst (Object dat, DLList owner)
   {
      throw new NoSuchElementException ("LeftEndNode.setFirst: Left end has no data.");
   }

   /**
   * Throws NoSuchElementException.
   * @param dllist
   */
   void setLeftRest (DLList dllist, DLList owner)
   // Pre: this node is the left node of owner.
   {
      throw new NoSuchElementException ("LeftEndNode.setLeftRest: Left end has no left tail.");
   }

   /**
   * @param algo
   * @param input
   * @param ownerList
   */
   Object executeLeft (IAlgoLeft algo, Object input, DLList owner)
   // Pre: this node is the left node of ownerList.
   {
      return algo.leftEndCase (owner, input);
   }

   /**
   * Throws IllegalStateException.  Can never be a the right node of a DLList
   * @param dllist the new tail that is to replace the current one.
   * @param owner the DLList that holds this ANode.
   */
   void setRightRest (DLList dllist, DLList owner)
   {
      throw new IllegalStateException ("Should never call LeftEnd.setRightRest ()");
   }

   /**
   * Throws IllegalStateException.  Can never be a the right node of a DLList
   * @param algo
   * @param input
   * @param owner
   * @return
   */
   Object executeRight (IAlgoRight algo, Object input, DLList owner)
   {
      throw new IllegalStateException ("Should never call LeftEnd.executeRight ()");
   }
}