package com.treelight.krnl;

import java.util.LinkedList;

/**
 * The prototype list header for a knowledge repository.
 * <p>
 * The list classes are fundamentally identical to the
 * (@linhk java.util.LinkedList} data type. In fact,
 * they delegate to an instance of that type. The
 * <i>only</i> reason for defining separate classes is
 * to achieve type safety in the add() and remove()
 * and get() and replace() operations.
 * 
 * @version 0.1
 * @author Eric Armstrong
 * @see ../NodesAndLists.html
 */
abstract public class AbstractList extends AbstractVersionedEntity {
  // The list data
  protected LinkedList list = new LinkedList();

  // These methods must be defined in the individual classes.
  // If defined here here, the arguments would have to be
  // abstract, forcing the subclasses to define them with the
  // abstract types as arguments, instead of the special 
  // types they must be restricted to.
  //  * add
  //  * remove
  //  * get
  //  * replace

  // These methods can be defined here.
  //  * iterator
  //  * ListIterator
  public Iterator iterator() {
    return list.iterator();
  }

  public ListIterator listIterator() {
    return list.listIterator();
  }

  //====================================================
  // ADDITIOINAL VERSIONING SUPPORT FOR LISTS
  //====================================================

  /** Version of the latest subentry, modified by reportChange(). */
  private VersionStamp latestEntryVersion;

  /** Returns the version of the latest entry in the sublist. */
  public VersionStamp getLatestEntryVersion() {
    return latestEntryVersion;
  }

  /** 
   * Records the version of the latest entry in the sublist,
   * making sure that the new version is in fact more recent. 
   * If it is, reports the change to all parents.
   */
  protected void reportChange(VersionStamp latestEntryVersion) {
    if (this.latestEntryVersion == null
    ||  this.latestEntryVersion.compare(entryVersion) == -1) {
      this.latestEntryVersion = entryVersion);
      //___TODO:___
    }
  }

}//AbstractList