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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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package io.sirix.service.xml.shredder;

import io.sirix.api.xml.XmlNodeTrx;
import io.sirix.exception.SirixException;
import io.sirix.node.NodeKind;
import io.sirix.service.InsertPosition;
import io.sirix.settings.Fixed;
import it.unimi.dsi.fastutil.longs.LongArrayList;
import it.unimi.dsi.fastutil.longs.LongStack;
import io.brackit.query.atomic.QNm;

import static java.util.Objects.requireNonNull;

/**
 * Skeleton implementation of {@link Shredder} interface methods.
 * 
 * All methods throw {@link NullPointerException}s in case of {@code null} values for reference
 * parameters and check the arguments, whereas in case they are not valid a
 * {@link IllegalArgumentException} is thrown.
 *
 * @author Johannes Lichtenberger, University of Konstanz
 * @author Marc Kramis, Seabix GmbH
 *
 */
public abstract class AbstractShredder implements Shredder {

  /** Sirix {@link XmlNodeTrx}. */
  private final XmlNodeTrx wtx;

  /** Keeps track of visited keys. */
  private final LongStack parents;

  /** Determines the import location of a new node. */
  private InsertPosition insertLocation;

  /**
   * Constructor.
   *
   * @throws NullPointerException if {@code wtx} is {@code null} or {@code insertLocation} is
   *         {@code null}
   */
  public AbstractShredder(final XmlNodeTrx wtx, final InsertPosition insertLocation) {
    this.wtx = requireNonNull(wtx);
    this.insertLocation = requireNonNull(insertLocation);
    parents = new LongArrayList();
    parents.push(Fixed.NULL_NODE_KEY.getStandardProperty());
  }

  @Override
  public void processComment(final String commentValue) throws SirixException {
    final String value = requireNonNull(commentValue);
    if (!value.isEmpty()) {
      final long key;

      if (parents.topLong() == Fixed.NULL_NODE_KEY.getStandardProperty()) {
        key = wtx.insertCommentAsFirstChild(value).getNodeKey();
      } else {
        key = wtx.insertCommentAsRightSibling(value).getNodeKey();
      }

      parents.popLong();
      parents.push(key);
    }
  }

  @Override
  public void processPI(final String processingContent, final String processingTarget) throws SirixException {
    final String content = requireNonNull(processingContent);
    final String target = requireNonNull(processingTarget);

    if (!target.isEmpty()) {
      final long key;

      if (parents.topLong() == Fixed.NULL_NODE_KEY.getStandardProperty()) {
        key = wtx.insertPIAsFirstChild(target, content).getNodeKey();
      } else {
        key = wtx.insertPIAsRightSibling(target, content).getNodeKey();
      }

      parents.popLong();
      parents.push(key);
    }
  }

  @Override
  public void processText(final String textValue) throws SirixException {
    final String text = requireNonNull(textValue);
    if (!text.isEmpty()) {
      final long key;

      if (parents.topLong() == Fixed.NULL_NODE_KEY.getStandardProperty()) {
        key = wtx.insertTextAsFirstChild(text).getNodeKey();
      } else {
        key = wtx.insertTextAsRightSibling(text).getNodeKey();
      }

      parents.popLong();
      parents.push(key);
    }
  }

  @Override
  public void processStartTag(final QNm elementName) throws SirixException {
    final QNm name = requireNonNull(elementName);
    long key;
    switch (insertLocation) {
      case AS_FIRST_CHILD -> {
        if (parents.topLong() == Fixed.NULL_NODE_KEY.getStandardProperty()) {
          key = wtx.insertElementAsFirstChild(name).getNodeKey();
        } else {
          key = wtx.insertElementAsRightSibling(name).getNodeKey();
        }
      }
      case AS_RIGHT_SIBLING -> {
        if (wtx.getKind() == NodeKind.XML_DOCUMENT
            || wtx.getParentKey() == Fixed.DOCUMENT_NODE_KEY.getStandardProperty()) {
          throw new IllegalStateException("Subtree can not be inserted as sibling of document root or the root-element!");
        }
        key = wtx.insertElementAsRightSibling(name).getNodeKey();
        insertLocation = InsertPosition.AS_FIRST_CHILD;
      }
      case AS_LEFT_SIBLING -> {
        if (wtx.getKind() == NodeKind.XML_DOCUMENT
            || wtx.getParentKey() == Fixed.DOCUMENT_NODE_KEY.getStandardProperty()) {
          throw new IllegalStateException("Subtree can not be inserted as sibling of document root or the root-element!");
        }
        key = wtx.insertElementAsLeftSibling(name).getNodeKey();
        insertLocation = InsertPosition.AS_FIRST_CHILD;
      }
      default -> throw new AssertionError();// Must not happen.
    }

    parents.popLong();
    parents.push(key);
    parents.push(Fixed.NULL_NODE_KEY.getStandardProperty());
  }

  @Override
  public void processEndTag(final QNm elementName) {
    parents.popLong();
    wtx.moveTo(parents.topLong());
  }

  @Override
  public void processEmptyElement(final QNm elementName) throws SirixException {
    processStartTag(elementName);
    processEndTag(elementName);
  }
}