/*
    * Licensed to the Apache Software Foundation (ASF) under one or more
    * contributor license agreements.  See the NOTICE file distributed with
    * this work for additional information regarding copyright ownership.
    * The ASF licenses this file to You 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
    *
    *     https://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 org.apache.commons.configuration2;
  
  import java.io.PrintWriter;
  import java.io.Reader;
  import java.io.Writer;
  import java.nio.charset.StandardCharsets;
  import java.util.List;
  import java.util.Objects;
  
  import javax.xml.parsers.SAXParser;
  import javax.xml.parsers.SAXParserFactory;
  
  import org.apache.commons.configuration2.convert.ListDelimiterHandler;
  import org.apache.commons.configuration2.ex.ConfigurationException;
  import org.apache.commons.configuration2.io.FileLocator;
  import org.apache.commons.configuration2.io.FileLocatorAware;
  import org.apache.commons.text.StringEscapeUtils;
  import org.w3c.dom.Document;
  import org.w3c.dom.Element;
  import org.w3c.dom.Node;
  import org.w3c.dom.NodeList;
  import org.xml.sax.Attributes;
  import org.xml.sax.InputSource;
  import org.xml.sax.XMLReader;
  import org.xml.sax.helpers.DefaultHandler;
  
  /**
   * This configuration implements the XML properties format introduced in Java, see
   * https://docs.oracle.com/javase/8/docs/api/java/util/Properties.html. An XML properties file looks like this:
   *
   * <pre>
   * &lt;?xml version="1.0"?&gt;
   * &lt;!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"&gt;
   * &lt;properties&gt;
   *   &lt;comment&gt;Description of the property list&lt;/comment&gt;
   *   &lt;entry key="key1"&gt;value1&lt;/entry&gt;
   *   &lt;entry key="key2"&gt;value2&lt;/entry&gt;
   *   &lt;entry key="key3"&gt;value3&lt;/entry&gt;
   * &lt;/properties&gt;
   * </pre>
   *
   * The Java runtime is not required to use this class. The default encoding for this configuration format is UTF-8.
   * Note that unlike {@code PropertiesConfiguration}, {@code XMLPropertiesConfiguration} does not support includes.
   *
   * <em>Note:</em>Configuration objects of this type can be read concurrently by multiple threads. However if one of
   * these threads modifies the object, synchronization has to be performed manually.
   *
   * @since 1.1
   */
  public class XMLPropertiesConfiguration extends BaseConfiguration implements FileBasedConfiguration, FileLocatorAware {
  
      /**
       * SAX Handler to parse a XML properties file.
       *
       * @since 1.2
       */
      private final class XMLPropertiesHandler extends DefaultHandler {
          /** The key of the current entry being parsed. */
          private String key;
  
          /** The value of the current entry being parsed. */
          private StringBuilder value = new StringBuilder();
  
          /** Indicates that a comment is being parsed. */
          private boolean inCommentElement;
  
          /** Indicates that an entry is being parsed. */
          private boolean inEntryElement;
  
          @Override
          public void characters(final char[] chars, final int start, final int length) {
              /**
               * We're currently processing an element. All character data from now until the next endElement() call will be the data
               * for this element.
               */
              value.append(chars, start, length);
          }
  
          @Override
          public void endElement(final String uri, final String localName, final String qName) {
              if (inCommentElement) {
                  // We've just finished a <comment> element so set the header
                 setHeader(value.toString());
                 inCommentElement = false;
             }
 
             if (inEntryElement) {
                 // We've just finished an <entry> element, so add the key/value pair
                 addProperty(key, value.toString());
                 inEntryElement = false;
             }
 
             // Clear the element value buffer
             value = new StringBuilder();
         }
 
         @Override
         public void startElement(final String uri, final String localName, final String qName, final Attributes attrs) {
             if ("comment".equals(qName)) {
                 inCommentElement = true;
             }
 
             if ("entry".equals(qName)) {
                 key = attrs.getValue("key");
                 inEntryElement = true;
             }
         }
     }
 
     /**
      * The default encoding (UTF-8 as specified by https://docs.oracle.com/javase/8/docs/api/java/util/Properties.html)
      */
     public static final String DEFAULT_ENCODING = StandardCharsets.UTF_8.name();
 
     /**
      * Default string used when the XML is malformed
      */
     private static final String MALFORMED_XML_EXCEPTION = "Malformed XML";
 
     /** The temporary file locator. */
     private FileLocator locator;
 
     /** Stores a header comment. */
     private String header;
 
     /**
      * Creates an empty XMLPropertyConfiguration object which can be used to synthesize a new Properties file by adding
      * values and then saving(). An object constructed by this constructor cannot be tickled into loading included files because
      * it cannot supply a base for relative includes.
      */
     public XMLPropertiesConfiguration() {
     }
 
     /**
      * Creates and loads the XML properties from the specified DOM node.
      *
      * @param element The non-null DOM element.
      * @throws ConfigurationException Error while loading the Element.
      * @since 2.0
      */
     public XMLPropertiesConfiguration(final Element element) throws ConfigurationException {
         load(Objects.requireNonNull(element, "element"));
     }
 
     /**
      * Escapes a property value before it is written to disk.
      *
      * @param value the value to be escaped
      * @return the escaped value
      */
     private String escapeValue(final Object value) {
         final String v = StringEscapeUtils.escapeXml10(String.valueOf(value));
         return String.valueOf(getListDelimiterHandler().escape(v, ListDelimiterHandler.NOOP_TRANSFORMER));
     }
 
     /**
      * Gets the header comment of this configuration.
      *
      * @return the header comment
      */
     public String getHeader() {
         return header;
     }
 
     /**
      * Initializes this object with a {@code FileLocator}. The locator is accessed during load and save operations.
      *
      * @param locator the associated {@code FileLocator}
      */
     @Override
     public void initFileLocator(final FileLocator locator) {
         this.locator = locator;
     }
 
     /**
      * Parses a DOM element containing the properties. The DOM element has to follow the XML properties format introduced in
      * Java, see https://docs.oracle.com/javase/8/docs/api/java/util/Properties.html
      *
      * @param element The DOM element
      * @throws ConfigurationException Error while interpreting the DOM
      * @since 2.0
      */
     public void load(final Element element) throws ConfigurationException {
         if (!element.getNodeName().equals("properties")) {
             throw new ConfigurationException(MALFORMED_XML_EXCEPTION);
         }
         final NodeList childNodes = element.getChildNodes();
         for (int i = 0; i < childNodes.getLength(); i++) {
             final Node item = childNodes.item(i);
             if (item instanceof Element) {
                 if (item.getNodeName().equals("comment")) {
                     setHeader(item.getTextContent());
                 } else if (item.getNodeName().equals("entry")) {
                     final String key = ((Element) item).getAttribute("key");
                     addProperty(key, item.getTextContent());
                 } else {
                     throw new ConfigurationException(MALFORMED_XML_EXCEPTION);
                 }
             }
         }
     }
 
     @Override
     public void read(final Reader in) throws ConfigurationException {
         final SAXParserFactory factory = SAXParserFactory.newInstance();
         factory.setNamespaceAware(false);
         factory.setValidating(true);
 
         try {
             final SAXParser parser = factory.newSAXParser();
 
             final XMLReader xmlReader = parser.getXMLReader();
             xmlReader.setEntityResolver((publicId, systemId) -> new InputSource(getClass().getClassLoader().getResourceAsStream("properties.dtd")));
             xmlReader.setContentHandler(new XMLPropertiesHandler());
             xmlReader.parse(new InputSource(in));
         } catch (final Exception e) {
             throw new ConfigurationException("Unable to parse the configuration file", e);
         }
 
         // todo: support included properties ?
     }
 
     /**
      * Writes the configuration as child to the given DOM node
      *
      * @param document The DOM document to add the configuration to.
      * @param parent The DOM parent node.
      * @since 2.0
      */
     public void save(final Document document, final Node parent) {
         final Element properties = document.createElement("properties");
         parent.appendChild(properties);
         if (getHeader() != null) {
             final Element comment = document.createElement("comment");
             properties.appendChild(comment);
             comment.setTextContent(StringEscapeUtils.escapeXml10(getHeader()));
         }
         forEach((k, v) -> {
             if (v instanceof List) {
                 writeProperty(document, properties, k, (List<?>) v);
             } else {
                 writeProperty(document, properties, k, v);
             }
         });
     }
 
     /**
      * Sets the header comment of this configuration.
      *
      * @param header the header comment
      */
     public void setHeader(final String header) {
         this.header = header;
     }
 
     @Override
     public void write(final Writer out) throws ConfigurationException {
         final PrintWriter writer = new PrintWriter(out);
         String encoding = locator != null ? locator.getEncoding() : null;
         if (encoding == null) {
             encoding = DEFAULT_ENCODING;
         }
         writer.println("<?xml version=\"1.0\" encoding=\"" + encoding + "\"?>");
         writer.println("<!DOCTYPE properties SYSTEM \"http://java.sun.com/dtd/properties.dtd\">");
         writer.println("<properties>");
         if (getHeader() != null) {
             writer.println("  <comment>" + StringEscapeUtils.escapeXml10(getHeader()) + "</comment>");
         }
         forEach((k, v) -> {
             if (v instanceof List) {
                 writeProperty(writer, k, (List<?>) v);
             } else {
                 writeProperty(writer, k, v);
             }
         });
         writer.println("</properties>");
         writer.flush();
     }
 
     private void writeProperty(final Document document, final Node properties, final String key, final List<?> values) {
         values.forEach(value -> writeProperty(document, properties, key, value));
     }
 
     private void writeProperty(final Document document, final Node properties, final String key, final Object value) {
         final Element entry = document.createElement("entry");
         properties.appendChild(entry);
 
         // escape the key
         final String k = StringEscapeUtils.escapeXml10(key);
         entry.setAttribute("key", k);
 
         if (value != null) {
             final String v = escapeValue(value);
             entry.setTextContent(v);
         }
     }
 
     /**
      * Writes a list property.
      *
      * @param out the output stream
      * @param key the key of the property
      * @param values a list with all property values
      */
     private void writeProperty(final PrintWriter out, final String key, final List<?> values) {
         values.forEach(value -> writeProperty(out, key, value));
     }
 
     /**
      * Writes a property.
      *
      * @param out the output stream
      * @param key the key of the property
      * @param value the value of the property
      */
     private void writeProperty(final PrintWriter out, final String key, final Object value) {
         // escape the key
         final String k = StringEscapeUtils.escapeXml10(key);
 
         if (value != null) {
             final String v = escapeValue(value);
             out.println("  <entry key=\"" + k + "\">" + v + "</entry>");
         } else {
             out.println("  <entry key=\"" + k + "\"/>");
         }
     }
 }