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'rapiddweller Common' is an open source Java library forked from Databene Commons by Volker Bergmann. It provides extensions to the Java core library by utility classes, abstract concepts and concrete implementations.
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/*
 * Copyright (C) 2004-2015 Volker Bergmann ([email protected]).
 * All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 * http://www.apache.org/licenses/LICENSE-2.0
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.rapiddweller.common.tree;

import com.rapiddweller.common.NullSafeComparator;
import com.rapiddweller.common.TreeModel;
import com.rapiddweller.common.iterator.BidirectionalIterator;

/**
 * Iterates a tree forward and backward.
 * Created: 08.05.2007 18:05:24
 *
 * @param  the type of object to iterate
 * @author Volker Bergmann
 */
public class TreeIterator implements BidirectionalIterator {

  private final TreeModel treeModel;
  private E cursor;

  private Boolean hasNext;
  private E next;
  private Boolean hasPrevious;
  private E previous;

  // constructors ----------------------------------------------------------------------------------------------------

  /**
   * Instantiates a new Tree iterator.
   *
   * @param treeModel the tree model
   */
  public TreeIterator(TreeModel treeModel) {
    this.treeModel = treeModel;
    this.cursor = treeModel.getRoot();
    this.hasNext = true;
    this.next = cursor;
    this.hasPrevious = null;
    this.previous = null;
  }

  // BidirectionalIterator interface implementation ------------------------------------------------------------------

  @Override
  public E first() {
    this.cursor = treeModel.getRoot();
    this.hasNext = null;
    this.next = null;
    this.hasPrevious = null;
    this.previous = null;
    return this.cursor;
  }

  @Override
  public boolean hasPrevious() {
    if (hasPrevious == null) {
      previous = nodeBefore(cursor, treeModel);
      hasPrevious = (previous != null);
    }
    return hasPrevious;
  }

  @Override
  public E previous() {
    if (!hasPrevious()) {
      throw new IllegalStateException("No object available for previous()");
    }
    hasNext = true;
    next = cursor;
    cursor = previous;
    hasPrevious = null;
    previous = null;
    return cursor;
  }

  @Override
  public E last() {
    hasNext = false;
    next = null;
    hasPrevious = null;
    previous = null;
    E tmp = lastChild(treeModel.getRoot(), treeModel);
    while (treeModel.getChildCount(tmp) > 0) {
      E candidate = lastChild(tmp, treeModel);
      if (candidate == null) {// empty directory
        cursor = tmp;
        return cursor;
      }
      tmp = candidate;
    }
    cursor = tmp;
    return cursor;
  }

  @Override
  public boolean hasNext() {
    if (hasNext == null) {
      next = nodeAfter(cursor, treeModel);
      hasNext = (next != null);
    }
    return hasNext;
  }

  @Override
  public E next() {
    if (!hasNext()) {
      throw new IllegalStateException("No object available for next()");
    }
    hasPrevious = true;
    previous = cursor;
    cursor = next;
    hasNext = null;
    next = null;
    return cursor;
  }

  @Override
  public void remove() {
    throw new UnsupportedOperationException("remove() is not supported on " + getClass());
  }

  // private helpers -------------------------------------------------------------------------------------------------

  private static  T nodeBefore(T cursor, TreeModel treeModel) {
    // root is the very first node
    if (cursor == treeModel.getRoot()) {
      return null;
    }
    // check previous siblings
    T parent = treeModel.getParent(cursor);
    for (int i = treeModel.getIndexOfChild(parent, cursor); i > 0; i--) {
      T tmp = treeModel.getChild(parent, i - 1);
      if (treeModel.getChildCount(tmp) == 0) {
        return tmp;
      } else {
        T candidate = lastSubNode(tmp, treeModel);
        if (candidate != null) {
          return candidate;
        }
      }
    }
    return parent;
  }

  private static  T lastChild(T node, TreeModel treeModel) {
    int childCount = treeModel.getChildCount(node);
    if (childCount > 0) {
      return treeModel.getChild(node, childCount - 1);
    } else {
      return null;
    }
  }

  private static  T lastSubNode(T node, TreeModel treeModel) {
    T candidate = lastChild(node, treeModel);
    while (candidate != null) {
      if (treeModel.getChildCount(candidate) == 0) {
        return candidate;
      } else {
        candidate = lastChild(candidate, treeModel);
      }
    }
    return null;
  }

  private static  T nodeAfter(T cursor, TreeModel treeModel) {
    // find next
    T tmp = null;
    if (treeModel.getChildCount(cursor) > 0) {
      tmp = treeModel.getChild(cursor, 0);
    }
    T parent = treeModel.getParent(cursor);
    if (tmp == null && parent != null) {
      int cursorIndex = treeModel.getIndexOfChild(parent, cursor);
      if (cursorIndex < treeModel.getChildCount(parent) - 1) {
        tmp = treeModel.getChild(parent, cursorIndex + 1);
      }
    }
    while (tmp == null && parent != null && !NullSafeComparator.equals(parent, treeModel.getRoot())) {
      T parentsParent = treeModel.getParent(parent);
      int parentsIndex = treeModel.getIndexOfChild(parentsParent, parent);
      int parentLevelCount = treeModel.getChildCount(parentsParent);
      if (parentsIndex < parentLevelCount - 1) {
        tmp = treeModel.getChild(parentsParent, parentsIndex + 1);
      }
      parent = parentsParent;
    }
    return tmp;
  }

}