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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.service.xml.serialize;

import io.sirix.access.DatabaseConfiguration;
import io.sirix.access.Databases;
import io.sirix.access.ResourceConfiguration;
import io.sirix.access.Utils;
import io.sirix.api.ResourceSession;
import io.sirix.api.xml.XmlNodeReadOnlyTrx;
import io.sirix.api.xml.XmlNodeTrx;
import io.sirix.api.xml.XmlResourceSession;
import io.sirix.exception.SirixException;
import io.sirix.node.NodeKind;
import io.sirix.service.AbstractSerializer;
import io.sirix.utils.LogWrapper;
import io.sirix.utils.XMLToken;
import io.brackit.query.atomic.QNm;
import org.checkerframework.checker.index.qual.NonNegative;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.slf4j.LoggerFactory;
import org.xml.sax.*;
import org.xml.sax.helpers.AttributesImpl;
import org.xml.sax.helpers.DefaultHandler;

import java.io.IOException;
import java.nio.file.Path;
import java.nio.file.Paths;

import static java.util.Objects.requireNonNull;

/**
 *
 * 
 * Generates SAX events from a Sirix database/resource.
 * 
 *
 * @author Johannes Lichtenberger, University of Konstanz
 *
 */
public final class SAXSerializer extends AbstractSerializer
    implements XMLReader {

  /** {@link LogWrapper} reference. */
  private final LogWrapper LOGGER = new LogWrapper(LoggerFactory.getLogger(SAXSerializer.class));

  /** SAX content handler. */
  private ContentHandler contentHandler;

  /**
   * Constructor.
   *
   * @param resMgr Sirix {@link ResourceSession}
   * @param handler SAX {@link ContentHandler}
   * @param revision revision to serialize
   * @param revisions further revisions to serialize
   */
  public SAXSerializer(final XmlResourceSession resMgr, final ContentHandler handler, final @NonNegative int revision,
      final int... revisions) {
    super(resMgr, null, revision, revisions);
    contentHandler = handler;
  }

  @Override
  protected void emitNode(final XmlNodeReadOnlyTrx rtx) {
    switch (rtx.getKind()) {
      case XML_DOCUMENT:
        break;
      case ELEMENT:
        generateElement(rtx);
        break;
      case TEXT:
        generateText(rtx);
        break;
      case COMMENT:
        generateComment(rtx);
        break;
      case PROCESSING_INSTRUCTION:
        generatePI(rtx);
        break;
      // $CASES-OMITTED$
      default:
        throw new UnsupportedOperationException("Node kind not supported by sirix!");
    }
  }

  @Override
  protected void emitEndNode(final XmlNodeReadOnlyTrx rtx, final boolean lastEndNode) {
    final QNm qName = rtx.getName();
    final String mURI = qName.getNamespaceURI();
    try {
      contentHandler.endPrefixMapping(qName.getPrefix());
      contentHandler.endElement(mURI, qName.getLocalName(), Utils.buildName(qName));
    } catch (final SAXException e) {
      LOGGER.error(e.getMessage(), e);
    }
  }

  @Override
  protected void emitRevisionStartNode(final @NonNull XmlNodeReadOnlyTrx rtx) {
    final int length = (revisions.length == 1 && revisions[0] < 0)
        ? resMgr.getMostRecentRevisionNumber()
        : revisions.length;

    if (length > 1) {
      final AttributesImpl atts = new AttributesImpl();
      atts.addAttribute("sdb", "revision", "sdb:revision", "", Integer.toString(rtx.getRevisionNumber()));
      try {
        contentHandler.startElement("https://sirix.io", "sirix-item", "sdb:sirix-item", atts);
      } catch (final SAXException e) {
        LOGGER.error(e.getMessage(), e);
      }
    }
  }

  @Override
  protected void emitRevisionEndNode(final @NonNull XmlNodeReadOnlyTrx rtx) {
    final int length = (revisions.length == 1 && revisions[0] < 0)
        ? (int) resMgr.getMostRecentRevisionNumber()
        : revisions.length;

    if (length > 1) {
      try {
        contentHandler.endElement("https://sirix.io", "sirix-item", "sdb:sirix-item");
      } catch (final SAXException e) {
        LOGGER.error(e.getMessage(), e);
      }
    }
  }

  /**
   * Generates a comment event.
   *
   * @param rtx {@link XmlNodeReadOnlyTrx} implementation
   */
  private void generateComment(final XmlNodeReadOnlyTrx rtx) {
    try {
      final char[] content = rtx.getValue().toCharArray();
      contentHandler.characters(content, 0, content.length);
    } catch (final SAXException e) {
      LOGGER.error(e.getMessage(), e);
    }
  }

  /**
   * Generate a processing instruction event.
   *
   * @param rtx {@link XmlNodeReadOnlyTrx} implementation
   */
  private void generatePI(final XmlNodeReadOnlyTrx rtx) {
    try {
      contentHandler.processingInstruction(rtx.getName().getLocalName(), rtx.getValue());
    } catch (final SAXException e) {
      LOGGER.error(e.getMessage(), e);
    }
  }

  /**
   * Generate a start element event.
   *
   * @param rtx {@link XmlNodeReadOnlyTrx} implementation
   */
  private void generateElement(final XmlNodeReadOnlyTrx rtx) {
    final AttributesImpl atts = new AttributesImpl();
    final long key = rtx.getNodeKey();

    try {
      // Process namespace nodes.
      for (int i = 0, namesCount = rtx.getNamespaceCount(); i < namesCount; i++) {
        rtx.moveToNamespace(i);
        final QNm qName = rtx.getName();
        contentHandler.startPrefixMapping(qName.getPrefix(), qName.getNamespaceURI());
        final String mURI = qName.getNamespaceURI();
        if (qName.getPrefix() == null || qName.getPrefix().length() == 0) {
          atts.addAttribute(mURI, "xmlns", "xmlns", "CDATA", mURI);
        } else {
          atts.addAttribute(mURI, "xmlns", "xmlns:" + rtx.getName().getPrefix(), "CDATA", mURI);
        }
        rtx.moveTo(key);
      }

      // Process attributes.
      for (int i = 0, attCount = rtx.getAttributeCount(); i < attCount; i++) {
        rtx.moveToAttribute(i);
        final QNm qName = rtx.getName();
        final String mURI = qName.getNamespaceURI();
        atts.addAttribute(mURI, qName.getLocalName(), Utils.buildName(qName), rtx.getType(), rtx.getValue());
        rtx.moveTo(key);
      }

      // Create SAX events.
      final QNm qName = rtx.getName();
      contentHandler.startElement(qName.getNamespaceURI(), qName.getLocalName(), Utils.buildName(qName), atts);

      // Empty elements.
      if (!rtx.hasFirstChild()) {
        contentHandler.endElement(qName.getNamespaceURI(), qName.getLocalName(), Utils.buildName(qName));
      }
    } catch (final SAXException e) {
      LOGGER.error(e.getMessage(), e);
    }
  }

  /**
   * Generate a text event.
   *
   * @param rtx {@link XmlNodeReadOnlyTrx} implementation
   */
  private void generateText(final XmlNodeReadOnlyTrx rtx) {
    try {
      contentHandler.characters(XMLToken.escapeContent(rtx.getValue()).toCharArray(), 0, rtx.getValue().length());
    } catch (final SAXException e) {
      LOGGER.error(e.getMessage(), e);
    }
  }

  @Override
  protected void setTrxForVisitor(XmlNodeReadOnlyTrx rtx) {}

  @Override
  protected boolean areSiblingNodesGoingToBeSkipped(XmlNodeReadOnlyTrx rtx) {
    return false;
  }

  @Override
  protected boolean isSubtreeGoingToBeVisited(final XmlNodeReadOnlyTrx rtx) {
    return true;
  }

  /**
   * Main method.
   *
   * @param args args[0] specifies the path to the sirix storage from which to generate SAX events.
   * @throws SirixException if any Sirix exception occurs
   */
  public static void main(final String... args) {
    final Path path = Paths.get(args[0]);
    final DatabaseConfiguration config = new DatabaseConfiguration(path);
    Databases.createXmlDatabase(config);
    final var database = Databases.openXmlDatabase(path);
    database.createResource(new ResourceConfiguration.Builder("shredded").build());
    try (final XmlResourceSession resource = database.beginResourceSession("shredded")) {
      final DefaultHandler defHandler = new DefaultHandler();
      final SAXSerializer serializer = new SAXSerializer(resource, defHandler, resource.getMostRecentRevisionNumber());
      serializer.call();
    }
  }

  @Override
  protected void emitStartDocument() {
    try {
      contentHandler.startDocument();

      final int length = (revisions.length == 1 && revisions[0] < 0)
          ? resMgr.getMostRecentRevisionNumber()
          : revisions.length;

      if (length > 1) {
        final String ns = "https://sirix.io";

        final AttributesImpl atts = new AttributesImpl();

        atts.addAttribute(ns, "xmlns", "xmlns:sdb", "", ns);

        contentHandler.startElement("sdb", "sirix", "sdb:sirix", atts);
      }
    } catch (final SAXException e) {
      LOGGER.error(e.getMessage(), e);
    }
  }

  @Override
  protected void emitEndDocument() {
    try {
      final int length = (revisions.length == 1 && revisions[0] < 0)
          ? (int) resMgr.getMostRecentRevisionNumber()
          : revisions.length;

      if (length > 1) {
        contentHandler.endElement("sdb", "sirix", "sdb:sirix");
      }

      contentHandler.endDocument();
    } catch (final SAXException e) {
      LOGGER.error(e.getMessage(), e);
    }
  }

  /* Implements XMLReader method. */
  @Override
  public ContentHandler getContentHandler() {
    return contentHandler;
  }

  /* Implements XMLReader method. */
  @Override
  public DTDHandler getDTDHandler() {
    return null;
  }

  /* Implements XMLReader method. */
  @Override
  public EntityResolver getEntityResolver() {
    return null;
  }

  /* Implements XMLReader method. */
  @Override
  public ErrorHandler getErrorHandler() {
    return null;
  }

  /* Implements XMLReader method. */
  @Override
  public boolean getFeature(String name) throws SAXNotRecognizedException, SAXNotSupportedException {
    throw new SAXNotSupportedException();
  }

  /* Implements XMLReader method. */
  @Override
  public Object getProperty(String name) throws SAXNotRecognizedException, SAXNotSupportedException {
    throw new SAXNotSupportedException();
  }

  /* Implements XMLReader method. */
  @Override
  public void parse(InputSource input) throws IOException, SAXException {
    throw new UnsupportedOperationException();
  }

  /* Implements XMLReader method. */
  @Override
  public void parse(String systemID) throws IOException, SAXException {
    emitStartDocument();
    try {
      super.call();
    } catch (final SirixException e) {
      LOGGER.error(e.getMessage(), e);
    }
    emitEndDocument();
  }

  /* Implements XMLReader method. */
  @Override
  public void setContentHandler(final ContentHandler contentHandler) {
    this.contentHandler = requireNonNull(contentHandler);
  }

  /* Implements XMLReader method. */
  @Override
  public void setDTDHandler(DTDHandler handler) {
    throw new UnsupportedOperationException();
  }

  /* Implements XMLReader method. */
  @Override
  public void setEntityResolver(EntityResolver resolver) {
    throw new UnsupportedOperationException();

  }

  /* Implements XMLReader method. */
  @Override
  public void setErrorHandler(ErrorHandler handler) {
    throw new UnsupportedOperationException();
  }

  /* Implements XMLReader method. */
  @Override
  public void setFeature(String name, boolean value) throws SAXNotRecognizedException, SAXNotSupportedException {
    throw new SAXNotSupportedException();
  }

  /* Implements XMLReader method. */
  @Override
  public void setProperty(String name, final Object value) throws SAXNotRecognizedException, SAXNotSupportedException {
    throw new SAXNotSupportedException();
  }
}