/* 
    * Licensed 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
    *
    * http://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.esigate.xml;
  
  import java.io.IOException;
  import java.io.StringReader;
  import java.io.Writer;
  
  import javax.xml.xpath.XPath;
  import javax.xml.xpath.XPathConstants;
  import javax.xml.xpath.XPathExpression;
  import javax.xml.xpath.XPathExpressionException;
  import javax.xml.xpath.XPathFactory;
  
  import nu.validator.htmlparser.common.DoctypeExpectation;
  import nu.validator.htmlparser.dom.Dom2Sax;
  import nu.validator.htmlparser.dom.HtmlDocumentBuilder;
  
  import org.esigate.Renderer;
  import org.esigate.impl.DriverRequest;
  import org.w3c.dom.Document;
  import org.w3c.dom.NodeList;
  import org.xml.sax.InputSource;
  import org.xml.sax.SAXException;
  
  /**
   * XML renderer.
   * <p>
   * Applies optional XPath evaluation and XSLT transformation to the retrieved data.
   * 
   * @author Stanislav Bernatskyi
   */
  public class XpathRenderer implements Renderer {
      private static final HtmlNamespaceContext HTML_NAMESPACE_CONTEXT = new HtmlNamespaceContext();
      private static final XPathFactory X_PATH_FACTORY = XPathFactory.newInstance();
      private final XPathExpression expr;
  
      public XpathRenderer(String xpath) {
          try {
              XPath xpathObj = X_PATH_FACTORY.newXPath();
              xpathObj.setNamespaceContext(HTML_NAMESPACE_CONTEXT);
              this.expr = xpathObj.compile(xpath);
          } catch (XPathExpressionException e) {
              throw new ProcessingFailedException("failed to compile XPath expression", e);
          }
      }
  
      /** {@inheritDoc} */
      @Override
      public void render(DriverRequest httpRequest, String src, Writer out) throws IOException {
          try {
              HtmlDocumentBuilder htmlDocumentBuilder = new HtmlDocumentBuilder();
              htmlDocumentBuilder.setDoctypeExpectation(DoctypeExpectation.NO_DOCTYPE_ERRORS);
              Document document = htmlDocumentBuilder.parse(new InputSource(new StringReader(src)));
              NodeList matchingNodes = (NodeList) expr.evaluate(document, XPathConstants.NODESET);
              XhtmlSerializer serializer = new XhtmlSerializer(out);
              Dom2Sax dom2Sax = new Dom2Sax(serializer, serializer);
              for (int i = 0; i < matchingNodes.getLength(); i++) {
                  dom2Sax.parse(matchingNodes.item(i));
              }
          } catch (XPathExpressionException e) {
              throw new ProcessingFailedException("Failed to evaluate XPath expression", e);
          } catch (SAXException e) {
              throw new ProcessingFailedException("Unable to parse source", e);
          }
      }
  }