// @(#) $Id: TwoWayNode.jml-refined,v 1.12 2007/11/13 11:45:56 chalin Exp $

// Copyright (C) 1998, 1999 Iowa State University

// This file is part of JML

// JML is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2, or (at your option)
// any later version.

// JML is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with JML; see the file COPYING.  If not, write to
// the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

// Author:  Clyde Ruby

package org.jmlspecs.samples.list.node;

//@ model import org.jmlspecs.models.JMLObjectSequence;

public class TwoWayNode extends OneWayNode { // Doubly Linked Node

    // data members

    /*@ public model JMLObjectSequence prevEntries;
      @                                in entries;
      @*/
    /*@ public model nullable TwoWayNode nextDL;
      @                         in nextNode;
      @*/

    //@ public invariant (nextNode == null || nextNode instanceof TwoWayNode);
    //@ public represents nextDL <- (TwoWayNode) nextNode;

    /*@ public model nullable TwoWayNode prevNode;
      @                         in prevEntries;
      @*/

    //@ public invariant_redundantly prevEntries != null;

  /*@ public normal_behavior
    @   assignable entries;
    @   ensures theEntry == null && entries.itemAt(0) == null 
    @       && entries.int_size() == 1 &&  prevEntries.isEmpty();
    @*/
    public TwoWayNode();

  /*@ public normal_behavior
    @   assignable entries;
    @   ensures theEntry == ent &&  entries.itemAt(0) == ent 
    @       && entries.int_size() == 1 &&  prevEntries.isEmpty();
    @*/
    public TwoWayNode(/*@ nullable @*/ Object ent);

  /*@ also
    @ public normal_behavior
    @   assignable entries;
    @   ensures \not_modified(prevEntries);
    @*/
    public void insertAfter(/*@ nullable @*/ Object newEntry);

  /*@ also
    @ public normal_behavior
    @   assignable entries;
    @   ensures \not_modified(prevEntries);
    @*/
    public void removeNextNode();

  /*@ public normal_behavior
    @   assignable \nothing;
    @   ensures \result == prevNode;
    @*/
    public /*@ pure nullable @*/ TwoWayNode getPrevNode();

  /*@ public normal_behavior
    @    assignable prevEntries;
    @    ensures prevEntries.equals(\old(prevEntries).insertBack(newEntry)) 
    @        && (nextNode != null ==> \not_modified(nextNode.entries));
    @*/
    public void insertBefore(/*@ nullable @*/ Object newEntry);

  /*@ also
    @  public normal_behavior
    @    assignable \nothing;
    @    ensures \result instanceof TwoWayNode
    @         && ((TwoWayNode)\result).entries.equals(entries)
    @         && ((TwoWayNode)\result).prevEntries.equals(prevEntries);
    @*/
    public Object clone();

}