/*
 * Copyright (c) 2010 by Intevation GmbH
 *
 * This program is free software under the LGPL (>=v2.1)
 * Read the file LGPL.txt coming with the software for details
 * or visit http://www.gnu.org/licenses/ if it does not exist.
 */

package de.intevation.artifactdatabase;

import java.io.File;
import java.io.IOException;
import java.io.OutputStream;

import javax.xml.namespace.NamespaceContext;
import javax.xml.namespace.QName;

import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerConfigurationException;
import javax.xml.transform.TransformerException;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.TransformerFactoryConfigurationError;

import javax.xml.transform.dom.DOMSource;

import javax.xml.transform.stream.StreamResult;

import javax.xml.xpath.XPath;
import javax.xml.xpath.XPathConstants;
import javax.xml.xpath.XPathExpressionException;
import javax.xml.xpath.XPathFactory;

import org.apache.log4j.Logger;

import org.w3c.dom.Attr;
import org.w3c.dom.Document;
import org.w3c.dom.Element;

import org.xml.sax.SAXException;

/**
 * Some helper functions to ease work with XML concering namespaces, XPATH
 * and so on.
 *  @author <a href="mailto:sascha.teichmann@intevation.de">Sascha L. Teichmann</a>
 */
public final class XMLUtils
{
    /**
     * W3C URL of XForms
     */
    public static final String XFORM_URL    = "http://www.w3.org/2002/xforms";
    /**
     * W3C prefix of XForms
     */
    public static final String XFORM_PREFIX = "xform";

    private static Logger logger = Logger.getLogger(XMLUtils.class);

    private XMLUtils() {
    }

    /**
     * Helper class to generate elements and attributes with
     * namespaces.
     */
    public static class ElementCreator
    {
        /**
         * owner document of the elements to be created
         */
        protected Document document;
        /**
         * namespace to be used
         */
        protected String   ns;
        /**
         * prefix to be used
         */
        protected String   prefix;

        /**
         * Constructor to create an element/attribute creator
         * with a given namespace and namespace prefix using a
         * given owner document.
         * @param document The owning document
         * @param ns       The namespace
         * @param prefix   The namespace prefix
         */
        public ElementCreator(Document document, String ns, String prefix) {
            this.document = document;
            this.ns       = ns;
            this.prefix   = prefix;
        }

        /**
         * Creates a new element using the owning document with
         * the this creators namespace and namespace prefix.
         * @param name The name of the element
         * @return     The new element
         */
        public Element create(String name) {
            Element element = document.createElementNS(ns, name);
            element.setPrefix(prefix);
            return element;
        }

        /**
         * Adds a new attribute and its value to a given element.
         * It does not set the namespace prefix.
         * @param element The element to add the attribute to
         * @param name    The name of the attribute
         * @param value   The value of the attribute
         */
        public void addAttr(Element element, String name, String value) {
            addAttr(element, name, value, false);
        }

        /**
         * Adds a new attribute and its value to a given element.
         * If the namespace prefix is used is decided by the 'addPrefix' flag.
         * @param element The element to add the attribute to
         * @param name    The name of the attribute
         * @param value   The value of the attribute
         * @param addPrefix If true the creators namespace prefix is
         * set on the attribute.
         */
        public void addAttr(
            Element element,
            String  name,
            String  value,
            boolean addPrefix
        ) {
            Attr attr = document.createAttributeNS(ns, name);
            attr.setValue(value);

            if (addPrefix)
                attr.setPrefix(prefix);

            element.setAttributeNode(attr);
        }
    } // class ElementCreator

    /**
     * Creates a new XML document
     * @return the new XML document ot null if something went wrong during
     * creation.
     */
    public static final Document newDocument() {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(true);

        try {
            return factory.newDocumentBuilder().newDocument();
        }
        catch (ParserConfigurationException pce) {
            logger.error(pce.getLocalizedMessage(), pce);
        }
        return null;
    }

    /**
     * Loads a XML document namespace aware from a file
     * @param file The file to load.
     * @return the XML document or null if something went wrong
     * during loading.
     */
    public static final Document parseDocument(File file) {
        DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();
        factory.setNamespaceAware(true);

        try {
            return factory.newDocumentBuilder().parse(file);
        }
        catch (ParserConfigurationException pce) {
            logger.error(pce.getLocalizedMessage(), pce);
        }
        catch (SAXException se) {
            logger.error(se.getLocalizedMessage(), se);
        }
        catch (IOException ioe) {
            logger.error(ioe.getLocalizedMessage(), ioe);
        }
        return null;
    }

    /**
     * Creates a new XPath without a namespace context.
     * @return the new XPath.
     */
    public static final XPath newXPath() {
        return newXPath(null);
    }

    /**
     * Creates a new XPath with a given namespace context.
     * @param namespaceContext The namespace context to be used or null
     * if none should be used.
     * @return The new XPath
     */
    public static final XPath newXPath(NamespaceContext namespaceContext) {
        XPathFactory factory = XPathFactory.newInstance();
        XPath        xpath   = factory.newXPath();
        if (namespaceContext != null) {
            xpath.setNamespaceContext(namespaceContext);
        }
        return xpath;
    }

    /**
     * Evaluates an XPath query on a given object and returns the result
     * as a given type. No namespace context is used.
     * @param root  The object which is used as the root of the tree to
     * be searched in.
     * @param query The XPath query
     * @param returnTyp The type of the result.
     * @return The result of type 'returnTyp' or null if something
     * went wrong during XPath evaluation.
     */
    public static final Object xpath(
        Object root,
        String query,
        QName  returnTyp
    ) {
        return xpath(root, query, returnTyp, null);
    }

    /**
     * Evaluates an XPath query on a given object and returns the result
     * as a string. A given namespace context is used.
     * @param root  The object which is used as the root of the tree to
     * be searched in.
     * @param query The XPath query
     * @param namespaceContext The namespace context to be used or null
     * if none should be used.
     * @return The result of the query or null if something went wrong
     * during XPath evaluation.
     */
    public static final String xpathString(
        Object root, String query, NamespaceContext namespaceContext
    ) {
        return (String)xpath(
            root, query, XPathConstants.STRING, namespaceContext);
    }

    /**
     * Evaluates an XPath query on a given object and returns the result
     * as a given type. Optionally a namespace context is used.
     * @param root The object which is used as the root of the tree to
     * be searched in.
     * @param query The XPath query
     * @param returnType The type of the result.
     * @param namespaceContext The namespace context to be used or null
     * if none should be used.
     * @return The result of type 'returnTyp' or null if something
     * went wrong during XPath evaluation.
     */
    public static final Object xpath(
        Object           root,
        String           query,
        QName            returnType,
        NamespaceContext namespaceContext
    ) {
        if (root == null) {
            return null;
        }

        try {
            XPath xpath = newXPath(namespaceContext);
            if (xpath != null) {
                return xpath.evaluate(query, root, returnType);
            }
        }
        catch (XPathExpressionException xpee) {
            logger.error(xpee.getLocalizedMessage(), xpee);
        }

        return null;
    }

    /**
     * Streams out an XML document to a given output stream.
     * @param document The document to be streamed out.
     * @param out      The output stream to be used.
     * @return true if operation succeeded else false.
     */
    public static boolean toStream(Document document, OutputStream out) {
        try {
            Transformer transformer =
                TransformerFactory.newInstance().newTransformer();
            DOMSource    source = new DOMSource(document);
            StreamResult result = new StreamResult(out);
            transformer.transform(source, result);
            return true;
        }
        catch (TransformerConfigurationException tce) {
            logger.error(tce.getLocalizedMessage(), tce);
        }
        catch (TransformerFactoryConfigurationError tfce) {
            logger.error(tfce.getLocalizedMessage(), tfce);
        }
        catch (TransformerException te) {
            logger.error(te.getLocalizedMessage(), te);
        }

        return false;
    }
}
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