/*
    * Licensed to The Apereo Foundation under one or more contributor license
    * agreements. See the NOTICE file distributed with this work for additional
    * information regarding copyright ownership.
    *
    *
    * The Apereo Foundation licenses this file to you under the Educational
    * Community 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://opensource.org/licenses/ecl2.txt
   *
   * 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 org.opencastproject.mediapackage;
  
  import static java.lang.String.format;
  import static javax.xml.XMLConstants.DEFAULT_NS_PREFIX;
  import static javax.xml.XMLConstants.W3C_XML_SCHEMA_INSTANCE_NS_URI;
  import static javax.xml.XMLConstants.XMLNS_ATTRIBUTE;
  import static javax.xml.XMLConstants.XML_NS_URI;
  import static org.opencastproject.util.EqualsUtil.hash;
  
  import org.opencastproject.util.RequireUtil;
  import org.opencastproject.util.XmlNamespaceBinding;
  import org.opencastproject.util.XmlNamespaceContext;
  import org.opencastproject.util.XmlSafeParser;
  
  import org.apache.commons.lang3.StringUtils;
  import org.w3c.dom.Document;
  import org.w3c.dom.Element;
  import org.w3c.dom.Node;
  import org.w3c.dom.bootstrap.DOMImplementationRegistry;
  import org.w3c.dom.ls.DOMImplementationLS;
  import org.w3c.dom.ls.LSOutput;
  import org.w3c.dom.ls.LSSerializer;
  import org.xml.sax.Attributes;
  
  import java.io.ByteArrayOutputStream;
  import java.io.IOException;
  import java.io.OutputStream;
  import java.io.Serializable;
  import java.nio.charset.StandardCharsets;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Comparator;
  import java.util.HashMap;
  import java.util.Iterator;
  import java.util.List;
  import java.util.Map;
  import java.util.Map.Entry;
  import java.util.stream.Collectors;
  
  import javax.xml.parsers.DocumentBuilder;
  import javax.xml.parsers.DocumentBuilderFactory;
  import javax.xml.parsers.ParserConfigurationException;
  import javax.xml.transform.TransformerException;
  
  /**
   * This is a basic implementation for handling simple catalogs of metadata. It provides utility methods to store
   * key-value data.
   * <p>
   * For a definition of the terms <dfn>expanded name</dfn>, <dfn>qualified name</dfn> or <dfn>QName</dfn>, <dfn>namespace
   * prefix</dfn>, <dfn>local part</dfn> and <dfn>local name</dfn>, please see <a
   * href="http://www.w3.org/TR/REC-xml-names">http://www.w3.org/TR/REC-xml-names</a>
   * <p>
   * By default the following namespace prefixes are bound:
   * <ul>
   * <li>xml - http://www.w3.org/XML/1998/namespace
   * <li>xmlns - http://www.w3.org/2000/xmlns/
   * <li>xsi - http://www.w3.org/2001/XMLSchema-instance
   * </ul>
   * <p>
   * <h2>Limitations</h2>
   * XMLCatalog supports only <em>one</em> prefix binding per namespace name, so you cannot create documents like the
   * following using XMLCatalog:
   *
   * <pre>
   * &lt;root xmlns:x=&quot;http://x.demo.org&quot; xmlns:y=&quot;http://x.demo.org&quot;&gt;
   *   &lt;x:elem&gt;value&lt;/x:elem&gt;
   *   &lt;y:elem&gt;value&lt;/y:elem&gt;
   * &lt;/root&gt;
   * </pre>
   *
   * However, reading of those documents is supported.
   */
  public abstract class XMLCatalogImpl extends CatalogImpl implements XMLCatalog {
    private static final long serialVersionUID = -7580292199527168951L;
  
    /** Expanded name of the XML language attribute <code>xml:lang</code>. */
    public static final EName XML_LANG_ATTR = new EName(XML_NS_URI, "lang");
  
   /** Namespace prefix for XML schema instance. */
   public static final String XSI_NS_PREFIX = "xsi";
 
   /** To marshaling empty fields to remove existing values during merge, default is not to marshal empty elements */
   protected boolean includeEmpty = false;
 
   /**
    * Expanded name of the XSI type attribute.
    * <p>
    * See <a href="http://www.w3.org/TR/xmlschema-1/#xsi_type">http://www.w3.org/TR/xmlschema-1/#xsi_type</a> for the
    * definition.
    */
   public static final EName XSI_TYPE_ATTR = new EName(W3C_XML_SCHEMA_INSTANCE_NS_URI, "type");
 
   /** Key (QName) value meta data */
   protected final Map<EName, List<CatalogEntry>> data = new HashMap<>();
 
   /** Namespace - prefix bindings */
   protected XmlNamespaceContext bindings;
 
   /**
    * Create an empty catalog and register the {@link javax.xml.XMLConstants#W3C_XML_SCHEMA_INSTANCE_NS_URI}
    * namespace.
    */
   protected XMLCatalogImpl() {
     super();
     bindings = XmlNamespaceContext.mk(XSI_NS_PREFIX, W3C_XML_SCHEMA_INSTANCE_NS_URI);
   }
 
   protected void addBinding(XmlNamespaceBinding binding) {
     bindings = bindings.add(binding);
   }
 
   protected XmlNamespaceContext getBindings() {
     return bindings;
   }
 
   /**
    * Clears the catalog.
    */
   protected void clear() {
     data.clear();
   }
 
   /**
    * Adds the element to the metadata collection.
    *
    * @param element
    *          the expanded name of the element
    * @param value
    *          the value
    */
   protected void addElement(EName element, String value) {
     if (element == null)
       throw new IllegalArgumentException("Expanded name must not be null");
 
     addElement(new CatalogEntry(element, value, NO_ATTRIBUTES));
   }
 
   /**
    * Adds the element with the <code>xml:lang</code> attribute to the metadata collection.
    *
    * @param element
    *          the expanded name of the element
    * @param value
    *          the value
    * @param language
    *          the language identifier (two letter ISO 639)
    */
   protected void addLocalizedElement(EName element, String value, String language) {
     RequireUtil.notNull(element, "expanded name");
     RequireUtil.notNull(language, "language");
 
     Map<EName, String> attributes = new HashMap<>(1);
     attributes.put(XML_LANG_ATTR, language);
     addElement(new CatalogEntry(element, value, attributes));
   }
 
   /**
    * Adds the element with the <code>xsi:type</code> attribute to the metadata collection.
    *
    * @param value
    *          the value
    * @param type
    *          the element type
    */
   protected void addTypedElement(EName element, String value, EName type) {
     RequireUtil.notNull(element, "expanded name");
     RequireUtil.notNull(type, "type");
 
     Map<EName, String> attributes = new HashMap<>(1);
     attributes.put(XSI_TYPE_ATTR, toQName(type));
     addElement(new CatalogEntry(element, value, attributes));
   }
 
   /**
    * Adds an element with the <code>xml:lang</code> and <code>xsi:type</code> attributes to the metadata collection.
    *
    * @param element
    *          the expanded name of the element
    * @param value
    *          the value
    * @param language
    *          the language identifier (two letter ISO 639)
    * @param type
    *          the element type
    */
   protected void addTypedLocalizedElement(EName element, String value, String language, EName type) {
     if (element == null)
       throw new IllegalArgumentException("EName name must not be null");
     if (type == null)
       throw new IllegalArgumentException("Type must not be null");
     if (language == null)
       throw new IllegalArgumentException("Language must not be null");
 
     Map<EName, String> attributes = new HashMap<>(2);
     attributes.put(XML_LANG_ATTR, language);
     attributes.put(XSI_TYPE_ATTR, toQName(type));
     addElement(new CatalogEntry(element, value, attributes));
   }
 
   /**
    * Adds an element with attributes to the catalog.
    *
    * @param element
    *          the expanded name of the element
    * @param value
    *          the element's value
    * @param attributes
    *          the attributes. May be null
    */
   protected void addElement(EName element, String value, Attributes attributes) {
     if (element == null)
       throw new IllegalArgumentException("Expanded name must not be null");
 
     Map<EName, String> attributeMap = new HashMap<>();
     if (attributes != null) {
       for (int i = 0; i < attributes.getLength(); i++) {
         attributeMap.put(new EName(attributes.getURI(i), attributes.getLocalName(i)), attributes.getValue(i));
       }
     }
     addElement(new CatalogEntry(element, value, attributeMap));
   }
 
   /**
    * Adds the catalog element to the list of elements.
    *
    * @param element
    *          the element
    */
   private void addElement(CatalogEntry element) {
 
     // Option includeEmpty allows marshaling empty elements
     // for deleting existing values during a catalog merge
     if (element == null)
       return;
     if (StringUtils.trimToNull(element.getValue()) == null && !includeEmpty)
       return;
     List<CatalogEntry> values = data.get(element.getEName());
     if (values == null) {
       values = new ArrayList<>();
       data.put(element.getEName(), values);
     }
     values.add(element);
   }
 
   /**
    * Completely removes an element.
    *
    * @param element
    *          the expanded name of the element
    */
   protected void removeElement(EName element) {
     removeValues(element, null, true);
   }
 
   /**
    * Removes all entries in a certain language from an element.
    *
    * @param element
    *          the expanded name of the element
    * @param language
    *          the language code (two letter ISO 639) or null to <em>only</em> remove entries without an
    *          <code>xml:lang</code> attribute
    */
   protected void removeLocalizedValues(EName element, String language) {
     removeValues(element, language, false);
   }
 
   /**
    * Removes values from an element or the complete element from the catalog.
    *
    * @param element
    *          the expanded name of the element
    * @param language
    *          the language code (two letter ISO 639) to remove or null to remove entries without language code
    * @param all
    *          true - remove all entries for that element. This parameter overrides the language parameter.
    */
   private void removeValues(EName element, String language, boolean all) {
     if (all) {
       data.remove(element);
     } else {
       List<CatalogEntry> entries = data.get(element);
       if (entries != null) {
         for (Iterator<CatalogEntry> i = entries.iterator(); i.hasNext();) {
           CatalogEntry entry = i.next();
           if (equal(language, entry.getAttribute(XML_LANG_ATTR))) {
             i.remove();
           }
         }
       }
     }
   }
 
   /**
    * Returns the values that are associated with the specified key.
    *
    * @param element
    *          the expanded name of the element
    * @return the elements
    */
   protected CatalogEntry[] getValues(EName element) {
     List<CatalogEntry> values = data.get(element);
     if (values != null && values.size() > 0) {
       return values.toArray(new CatalogEntry[values.size()]);
     }
     return new CatalogEntry[] {};
   }
 
   protected List<CatalogEntry> getEntriesSorted() {
     return data.values().stream()
         .flatMap(List::stream)
         .sorted(catalogEntryComparator)
         .collect(Collectors.toList());
   }
 
   /**
    * Returns the values that are associated with the specified key.
    *
    * @param element
    *          the expanded name of the element
    * @return all values of the element or an empty list if this element does not exist or does not have any values
    */
   @SuppressWarnings("unchecked")
   protected List<CatalogEntry> getValuesAsList(EName element) {
     List<CatalogEntry> values = data.get(element);
     return values != null ? values : Collections.EMPTY_LIST;
   }
 
   /**
    * Returns the values that are associated with the specified key.
    *
    * @param element
    *          the expandend name of the element
    * @param language
    *          a language code or null to get values without <code>xml:lang</code> attribute
    * @return all values of the element
    */
   @SuppressWarnings("unchecked")
   protected List<CatalogEntry> getLocalizedValuesAsList(EName element, String language) {
     List<CatalogEntry> values = data.get(element);
 
     if (values != null) {
       List<CatalogEntry> filtered = new ArrayList<>();
       for (CatalogEntry value : values) {
         if (equal(language, value.getAttribute(XML_LANG_ATTR))) {
           filtered.add(value);
         }
       }
       return filtered;
     } else {
       return Collections.EMPTY_LIST;
     }
   }
 
   /**
    * Returns the first value that is associated with the specified name.
    *
    * @param element
    *          the expanded name of the element
    * @return the first value
    */
   protected CatalogEntry getFirstValue(EName element) {
     List<CatalogEntry> elements = data.get(element);
     if (elements != null && elements.size() > 0) {
       return elements.get(0);
     }
     return null;
   }
 
   /**
    * Returns the first element that is associated with the specified name and attribute.
    *
    * @param element
    *          the expanded name of the element
    * @param attributeEName
    *          the expanded attribute name
    * @param attributeValue
    *          the attribute value
    * @return the first value
    */
   protected CatalogEntry getFirstValue(EName element, EName attributeEName, String attributeValue) {
     List<CatalogEntry> elements = data.get(element);
     if (elements != null) {
       for (CatalogEntry entry : elements) {
         String v = entry.getAttribute(attributeEName);
         if (equal(attributeValue, v))
           return entry;
       }
     }
     return null;
   }
 
   /**
    * Returns the first value that is associated with the specified name and language.
    *
    * @param element
    *          the expanded name of the element
    * @param language
    *          the language identifier or null to get only elements without <code>xml:lang</code> attribute
    * @return the first value
    */
   protected CatalogEntry getFirstLocalizedValue(EName element, String language) {
     return getFirstValue(element, XML_LANG_ATTR, language);
   }
 
   /**
    * Returns the first value that is associated with the specified name and language.
    *
    * @param element
    *          the expanded name of the element
    * @param type
    *          the <code>xsi:type</code> value
    * @return the element
    */
   protected CatalogEntry getFirstTypedValue(EName element, String type) {
     return getFirstValue(element, XSI_TYPE_ATTR, type);
   }
 
   /**
    * Tests two objects for equality.
    */
   protected boolean equal(Object a, Object b) {
     return (a == null && b == null) || (a != null && a.equals(b));
   }
 
   /**
    * Creates an xml document root and returns it.
    *
    * @return the document
    * @throws ParserConfigurationException
    *           If the xml parser environment is not correctly configured
    */
   protected Document newDocument() throws ParserConfigurationException {
     DocumentBuilderFactory docBuilderFactory = XmlSafeParser.newDocumentBuilderFactory();
     docBuilderFactory.setNamespaceAware(true);
     DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
     return docBuilder.newDocument();
   }
 
   /**
    * @see org.opencastproject.mediapackage.AbstractMediaPackageElement#toManifest(org.w3c.dom.Document,
    *      org.opencastproject.mediapackage.MediaPackageSerializer)
    */
   @Override
   public Node toManifest(Document document, MediaPackageSerializer serializer) throws MediaPackageException {
     return super.toManifest(document, serializer);
   }
 
   /**
    * Get a prefix from {@link #bindings} but throw a {@link NamespaceBindingException} if none found.
    */
   protected String getPrefix(String namespaceURI) {
     final String prefix = bindings.getPrefix(namespaceURI);
     if (prefix != null) {
       return prefix;
     } else {
       throw new NamespaceBindingException(format("Namespace URI %s is not bound to a prefix", namespaceURI));
     }
   }
 
   /**
    * @see org.opencastproject.mediapackage.XMLCatalog#includeEmpty(boolean)
    */
   @Override
   public
   void includeEmpty(boolean includeEmpty) {
     this.includeEmpty = includeEmpty;
   }
 
   /**
    * Transform an expanded name to a qualified name based on the registered binding.
    *
    * @param eName
    *          the expanded name to transform
    * @return the qualified name, e.g. <code>dcterms:title</code>
    * @throws NamespaceBindingException
    *           if the namespace name is not bound to a prefix
    */
   protected String toQName(EName eName) {
     if (eName.hasNamespace()) {
       return toQName(getPrefix(eName.getNamespaceURI()), eName.getLocalName());
     } else {
       return eName.getLocalName();
     }
   }
 
   /**
    * Transform an qualified name consisting of prefix and local part to an expanded name, based on the registered
    * binding.
    *
    * @param prefix
    *          the prefix
    * @param localName
    *          the local part
    * @return the expanded name
    * @throws NamespaceBindingException
    *           if the namespace name is not bound to a prefix
    */
   protected EName toEName(String prefix, String localName) {
     return new EName(bindings.getNamespaceURI(prefix), localName);
   }
 
   /**
    * Transform a qualified name to an expanded name, based on the registered binding.
    *
    * @param qName
    *          the qualified name, e.g. <code>dcterms:title</code> or <code>title</code>
    * @return the expanded name
    * @throws NamespaceBindingException
    *           if the namespace name is not bound to a prefix
    */
   protected EName toEName(String qName) {
     String[] parts = splitQName(qName);
     return new EName(bindings.getNamespaceURI(parts[0]), parts[1]);
   }
 
   /**
    * Splits a QName into its parts.
    *
    * @param qName
    *          the qname to split
    * @return an array of prefix (0) and local part (1). The prefix is "" if the qname belongs to the default namespace.
    */
   private static String[] splitQName(String qName) {
     final String[] parts = qName.split(":", 3);
     switch (parts.length) {
       case 1:
         return new String[] { DEFAULT_NS_PREFIX, parts[0] };
       case 2:
         return parts;
       default:
         throw new IllegalArgumentException("Local name must not contain ':'");
     }
   }
 
   /**
    * Returns a "prefixed name" consisting of namespace prefix and local name.
    *
    * @param prefix
    *          the namespace prefix, may be <code>null</code>
    * @param localName
    *          the local name
    * @return the "prefixed name" <code>prefix:localName</code>
    */
   private static String toQName(String prefix, String localName) {
     final StringBuilder b = new StringBuilder();
     if (prefix != null && !DEFAULT_NS_PREFIX.equals(prefix)) {
       b.append(prefix);
       b.append(":");
     }
     b.append(localName);
     return b.toString();
   }
 
   // --------------------------------------------------------------------------------------------
 
   private static final Map<EName, String> NO_ATTRIBUTES = new HashMap<>();
 
   CatalogEntry mkCatalogEntry(EName name, String value, Map<EName, String> attributes) {
     return new CatalogEntry(name, value, attributes);
   }
 
   /**
    * Element representation.
    */
   public final class CatalogEntry implements XmlElement, Comparable<CatalogEntry>, Serializable {
 
     /** The serial version UID */
     private static final long serialVersionUID = 7195298081966562710L;
 
     private final EName name;
 
     private final String value;
 
     /** The attributes of this element */
     private final Map<EName, String> attributes;
 
     /**
      * Creates a new catalog element representation with name, value and attributes.
      *
      * @param value
      *          the element value
      * @param attributes
      *          the element attributes
      */
     public CatalogEntry(EName name, String value, Map<EName, String> attributes) {
       this.name = name;
       this.value = value;
       this.attributes = new HashMap<>(attributes);
     }
 
     /**
      * Returns the qualified name of the entry as a string. The namespace of the entry has to be bound to a prefix for
      * this method to succeed.
      */
     public String getQName() {
       return toQName(name);
     }
 
     /**
      * Returns the expanded name of the entry.
      */
     public EName getEName() {
       return name;
     }
 
     /**
      * Returns the element value.
      *
      * @return the value
      */
     public String getValue() {
       return value;
     }
 
     /**
      * Returns <code>true</code> if the element contains attributes.
      *
      * @return <code>true</code> if the element contains attributes
      */
     public boolean hasAttributes() {
       return attributes.size() > 0;
     }
 
     /**
      * Returns the element's attributes.
      *
      * @return the attributes
      */
     public Map<EName, String> getAttributes() {
       return Collections.unmodifiableMap(attributes);
     }
 
     /**
      * Returns <code>true</code> if the element contains an attribute with the given name.
      *
      * @return <code>true</code> if the element contains the attribute
      */
     public boolean hasAttribute(EName name) {
       return attributes.containsKey(name);
     }
 
     /**
      * Returns the attribute value for the given attribute.
      *
      * @return the attribute or null
      */
     public String getAttribute(EName name) {
       return attributes.get(name);
     }
 
     @Override
     public int hashCode() {
       return hash(name, value);
     }
 
     @Override
     public boolean equals(Object that) {
       return (this == that) || (that instanceof CatalogEntry && eqFields((CatalogEntry) that));
     }
 
     private boolean eqFields(CatalogEntry that) {
       return this.compareTo(that) == 0;
     }
 
     /**
      * Returns the XML representation of this entry.
      *
      * @param document
      *          the document
      * @return the xml node
      */
     @Override
     public Node toXml(Document document) {
       Element node = document.createElement(toQName(name));
       // Write prefix binding to document root element
       bindNamespaceFor(document, name);
 
       List<EName> keySet = new ArrayList<>(attributes.keySet());
       Collections.sort(keySet);
       for (EName attrEName : keySet) {
         String value = attributes.get(attrEName);
         if (attrEName.hasNamespace()) {
           // Write prefix binding to document root element
           bindNamespaceFor(document, attrEName);
           if (XSI_TYPE_ATTR.equals(attrEName)) {
             // Special treatment for xsi:type attributes
             try {
               EName typeName = toEName(value);
               bindNamespaceFor(document, typeName);
             } catch (NamespaceBindingException ignore) {
               // Type is either not a QName or its namespace is not bound.
               // We decide to gently ignore those cases.
             }
           }
         }
         node.setAttribute(toQName(attrEName), value);
       }
       if (value != null) {
         node.appendChild(document.createTextNode(value));
       }
       return node;
     }
 
     /**
      * Compare two catalog entries. Comparison order:
      * - e_name
      * - number of attributes (less come first)
      * - attribute comparison (e_name -&gt; value)
      */
     @Override
     public int compareTo(CatalogEntry o) {
       int c = getEName().compareTo(o.getEName());
       if (c != 0) {
         return c;
       }
 
       c = Integer.compare(attributes.size(), o.attributes.size());
       if (c != 0) {
         return c;
       }
 
       // Sort attribute entries by attributeComparator
       List<Entry<EName, String>> thisAttrs = attributes.entrySet().stream()
           .sorted(attributeComparator)
           .toList();
 
       List<Entry<EName, String>> otherAttrs = o.attributes.entrySet().stream()
           .sorted(attributeComparator)
           .toList();
 
       // Compare entries pairwise
       for (int i = 0; i < thisAttrs.size(); i++) {
         c = attributeComparator.compare(thisAttrs.get(i), otherAttrs.get(i));
         if (c != 0) {
           return c;
         }
       }
 
       return 0; // all equal
     }
 
     /**
      * Writes a namespace binding for catalog entry <code>name</code> to the documents root element.
      * <code>xmlns:prefix="namespace"</code>
      */
     private void bindNamespaceFor(Document document, EName name) {
       Element root = (Element) document.getFirstChild();
       String namespace = name.getNamespaceURI();
       // Do not bind the "xml" namespace. It is bound by default
       if (!XML_NS_URI.equals(namespace)) {
         root.setAttribute(XMLNS_ATTRIBUTE + ":" + XMLCatalogImpl.this.getPrefix(name.getNamespaceURI()),
                 name.getNamespaceURI());
       }
     }
 
     @Override
     public String toString() {
       return value;
     }
   }
 
   static int doCompareTo(EName k1, String v1, EName k2, String v2) {
     final int c = k1.compareTo(k2);
     return c != 0 ? c : v1.compareTo(v2);
   }
 
   private static final Comparator<Map.Entry<EName, String>> attributeComparator =
       new Comparator<Map.Entry<EName, String>>() {
         @Override public int compare(Entry<EName, String> o1, Entry<EName, String> o2) {
           return doCompareTo(o1.getKey(), o1.getValue(), o2.getKey(), o2.getValue());
         }
       };
 
   private static final Comparator<CatalogEntry> catalogEntryComparator =
       new Comparator<CatalogEntry>() {
         @Override public int compare(CatalogEntry o1, CatalogEntry o2) {
           return o1.compareTo(o2);
         }
       };
 
   // --------------------------------------------------------------------------------------------
 
   // --
 
   /**
    * {@inheritDoc}
    *
    * @see org.opencastproject.mediapackage.XMLCatalog#toXml(java.io.OutputStream, boolean)
    */
   @Override
   public void toXml(OutputStream out, boolean format) throws IOException {
     try {
       Document doc = this.toXml();
       DOMImplementationRegistry reg = DOMImplementationRegistry.newInstance();
       DOMImplementationLS impl = (DOMImplementationLS) reg.getDOMImplementation("LS");
       LSSerializer serializer = impl.createLSSerializer();
       serializer.getDomConfig().setParameter("format-pretty-print", format);
       LSOutput output = impl.createLSOutput();
       output.setByteStream(out);
       serializer.write(doc, output);
     } catch (ParserConfigurationException e) {
       throw new IOException("unable to parse document");
     } catch (TransformerException e) {
       throw new IOException("unable to transform dom to a stream");
     } catch (ClassNotFoundException | IllegalAccessException | InstantiationException e) {
       throw new IOException("unable to serialize DOM");
     }
   }
 
   /**
    * {@inheritDoc}
    *
    * @see org.opencastproject.mediapackage.XMLCatalog#toXmlString()
    */
   @Override
   public String toXmlString() throws IOException {
     ByteArrayOutputStream out = new ByteArrayOutputStream();
     toXml(out, true);
     return new String(out.toByteArray(), StandardCharsets.UTF_8);
   }
 
 }