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SirixDB is a hybrid on-disk and in-memory document oriented, versioned database system. It has a lightweight buffer manager, stores everything in a huge persistent and durable tree and allows efficient reconstruction of every revision. Furthermore, SirixDB implements change tracking, diffing and supports time travel queries.

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/**
 * Copyright (c) 2011, University of Konstanz, Distributed Systems Group All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification, are permitted
 * provided that the following conditions are met: * Redistributions of source code must retain the
 * above copyright notice, this list of conditions and the following disclaimer. * Redistributions
 * in binary form must reproduce the above copyright notice, this list of conditions and the
 * following disclaimer in the documentation and/or other materials provided with the distribution.
 * * Neither the name of the University of Konstanz nor the names of its contributors may be used to
 * endorse or promote products derived from this software without specific prior written permission.
 * 
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
 * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL  BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */
package io.sirix.diff.export;

import java.util.ArrayList;
import java.util.IdentityHashMap;
import java.util.Iterator;
import java.util.List;
import java.util.NoSuchElementException;
import io.sirix.diff.DiffFactory.DiffType;
import io.sirix.diff.DiffTuple;

/**
 * Builds an edit script.
 * 
 * @author Johannes Lichtenberger, University of Konstanz
 * 
 */
public final class EditScript implements Iterator, Iterable {

  /** Preserves the order of changes and is used to iterate over all changes. */
  private final List mChanges;

  /** To do a lookup; we use node/object identities. */
  private final IdentityHashMap mChangeByNode;

  /** Index in the {@link List} of {@link DiffTuple}s. */
  private transient int mIndex;

  /**
   * Constructor.
   */
  public EditScript() {
    mChanges = new ArrayList();
    mChangeByNode = new IdentityHashMap();
    mIndex = 0;
  }

  /**
   * Calculates the size of the edit script. This can be used to estimate the amicability of an
   * algorithm.
   * 
   * @return number of changes
   */
  public int size() {
    return mChanges.size();
  }

  /**
   * Checks if the edit script is empty.
   * 
   * @return true if empty
   */
  public boolean isEmpty() {
    return mChanges.isEmpty();
  }

  /**
   * Checks if a node has been added(changed).
   * 
   * @param key key of node
   * @return true if the changes {@link List} already contains the nodeKey, false otherwise
   */
  public boolean containsNode(final long key) {
    if (key < 0) {
      throw new IllegalArgumentException("paramKey may not be < 0!");
    }
    return mChangeByNode.containsKey(key);
  }

  /**
   * Clears the edit script.
   */
  public void clear() {
    mChanges.clear();
    mChangeByNode.clear();
  }

  /**
   * Look up a change for the given nodeKey.
   * 
   * @param paramKey (not) changed key of node
   * @return the change assigned to the node or null
   */
  public DiffTuple get(final long paramKey) {
    return mChangeByNode.get(paramKey);
  }

  /**
   * Adds a change to the edit script.
   * 
   * @param change {@link DiffTuple} reference
   * @return the change
   */
  public DiffTuple add(final DiffTuple change) {
    assert change != null;
    final long nodeKey =
        change.getDiff() == DiffType.DELETED ? change.getOldNodeKey() : change.getNewNodeKey();
    if (mChangeByNode.containsKey(nodeKey)) {
      return change;
    }

    mChanges.add(change);
    return mChangeByNode.put(nodeKey, change);
  }

  @Override
  public Iterator iterator() {
    return mChanges.iterator();
  }

  @Override
  public boolean hasNext() {
    if (mIndex < mChanges.size() - 1) {
      return true;
    }
    return false;
  }

  @Override
  public DiffTuple next() {
    if (mIndex < mChanges.size()) {
      return mChanges.get(mIndex++);
    } else {
      throw new NoSuchElementException("No more elements in the change list!");
    }
  }

  @Override
  public void remove() {
    throw new UnsupportedOperationException("Remove is not supported!");
  }

}