/*
 *
 * Copyright (c) 2013 - 2017 Lijun Liao
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License version 3
 * as published by the Free Software Foundation with the addition of the
 * following permission added to Section 15 as permitted in Section 7(a):
 *
 * FOR ANY PART OF THE COVERED WORK IN WHICH THE COPYRIGHT IS OWNED BY
 * THE AUTHOR LIJUN LIAO. LIJUN LIAO DISCLAIMS THE WARRANTY OF NON INFRINGEMENT
 * OF THIRD PARTY RIGHTS.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU Affero General Public License for more details.
 *
 * You should have received a copy of the GNU Affero General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 *
 * The interactive user interfaces in modified source and object code versions
 * of this program must display Appropriate Legal Notices, as required under
 * Section 5 of the GNU Affero General Public License.
 *
 * You can be released from the requirements of the license by purchasing
 * a commercial license. Buying such a license is mandatory as soon as you
 * develop commercial activities involving the XiPKI software without
 * disclosing the source code of your own applications.
 *
 * For more information, please contact Lijun Liao at this
 * address: lijun.liao@gmail.com
 */

package org.xipki.pki.ca.dbtool.diffdb.io;

import java.io.IOException;
import java.io.InputStream;
import java.io.StringReader;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
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 org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;
import org.xipki.commons.common.util.ParamUtil;
import org.xml.sax.EntityResolver;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

/**
 * @author Lijun Liao
 * @since 2.0.0
 */

public class XmlDocumentReader {

    private final Document doc;

    private final XPathFactory xpathfactory;

    public XmlDocumentReader(final InputStream xmlStream, final boolean namespaceAware)
            throws ParserConfigurationException, SAXException, IOException {
        ParamUtil.requireNonNull("xmlStream", xmlStream);

        DocumentBuilderFactory builderFactory = DocumentBuilderFactory.newInstance();
        builderFactory.setNamespaceAware(namespaceAware);
        DocumentBuilder newDocumentBuilder = builderFactory.newDocumentBuilder();
        disableDtdValidation(newDocumentBuilder);
        doc = newDocumentBuilder.parse(xmlStream);

        xpathfactory = XPathFactory.newInstance();
    }

    private static void disableDtdValidation(final DocumentBuilder db) {
        db.setEntityResolver(new EntityResolver() {
            @Override
            public InputSource resolveEntity(final String publicId, final String systemId)
                    throws SAXException, IOException {
                return new InputSource(new StringReader(""));
            }
        });
    }

    public String getValue(final String xpathExpression) throws XPathExpressionException {
        ParamUtil.requireNonNull("xpathExpression", xpathExpression);
        Node node = getNode(xpathExpression);
        return (node != null) ? node.getFirstChild().getTextContent() : null;
    }

    private Node getNode(final String xpathExpression) throws XPathExpressionException {
        XPath xpath = xpathfactory.newXPath();
        XPathExpression xpathE = xpath.compile(xpathExpression);
        NodeList nl = (NodeList) xpathE.evaluate(doc.getDocumentElement(), XPathConstants.NODESET);
        if (nl != null && nl.getLength() > 0) {
            return nl.item(0);
        }

        return null;
    }

}