package de.lmu.ifi.dbs.elki.index.tree;

/*
 This file is part of ELKI:
 Environment for Developing KDD-Applications Supported by Index-Structures

 Copyright (C) 2015
 Ludwig-Maximilians-Universität München
 Lehr- und Forschungseinheit für Datenbanksysteme
 ELKI Development Team

 This program is free software: you can redistribute it and/or modify
 it under the terms of the GNU Affero General Public License as published by
 the Free Software Foundation, either version 3 of the License, or
 (at your option) any later version.

 This program 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 Affero General Public License for more details.

 You should have received a copy of the GNU Affero General Public License
 along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

import java.util.Enumeration;

import de.lmu.ifi.dbs.elki.persistent.Page;

/**
 * This interface defines the common requirements of nodes in an index
 * structure. A node has to extend the page interface for persistent storage and
 * has to provide an enumeration over its children.
 * 
 * @author Elke Achtert
 * @since 0.2
 * 
 * @apiviz.composedOf Entry
 * @apiviz.excludeSubtypes
 * 
 * @param <E> the type of Entry used in the index
 */
public interface Node<E extends Entry> extends Page {
  /**
   * Returns an enumeration of the children paths of this node.
   * 
   * @param parentPath the path to this node
   * @return an enumeration of the children paths of this node
   */
  Enumeration<IndexTreePath<E>> children(IndexTreePath<E> parentPath);

  /**
   * Returns the number of entries of this node.
   * 
   * @return the number of entries of this node
   */
  int getNumEntries();

  /**
   * Returns true if this node is a leaf node, false otherwise.
   * 
   * @return true if this node is a leaf node, false otherwise
   */
  boolean isLeaf();

  /**
   * Returns the entry at the specified index.
   * 
   * @param index the index of the entry to be returned
   * @return the entry at the specified index
   */
  E getEntry(int index);

  /**
   * Adds a new leaf entry to this node's children and returns the index of the
   * entry in this node's children array. An UnsupportedOperationException will
   * be thrown if the entry is not a leaf entry or this node is not a leaf node.
   * 
   * @param entry the leaf entry to be added
   * @return the index of the entry in this node's children array
   * @throws UnsupportedOperationException if entry is not a leaf entry or this
   *         node is not a leaf node
   */
  int addLeafEntry(E entry);

  /**
   * Adds a new directory entry to this node's children and returns the index of
   * the entry in this node's children array. An UnsupportedOperationException
   * will be thrown if the entry is not a directory entry or this node is not a
   * directory node.
   * 
   * @param entry the directory entry to be added
   * @return the index of the entry in this node's children array
   * @throws UnsupportedOperationException if entry is not a directory entry or
   *         this node is not a directory node
   */
  int addDirectoryEntry(E entry);
}