/*
 * Copyright (C) 2010 eXo Platform SAS.
 *
 * This is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation; either version 2.1 of
 * the License, or (at your option) any later version.
 *
 * This software 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
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this software; if not, write to the Free
 * Software Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
 * 02110-1301 USA, or see the FSF site: http://www.fsf.org.
 */

package org.exoplatform.commons.xml;

import java.io.IOException;
import java.io.Writer;

import javax.xml.stream.XMLOutputFactory;
import javax.xml.stream.XMLStreamException;
import javax.xml.stream.XMLStreamWriter;

import org.exoplatform.commons.utils.HTMLEntityEncoder;
import org.exoplatform.services.log.ExoLogger;
import org.exoplatform.services.log.Log;
import org.w3c.dom.Attr;
import org.w3c.dom.CDATASection;
import org.w3c.dom.CharacterData;
import org.w3c.dom.Element;
import org.w3c.dom.NamedNodeMap;
import org.w3c.dom.Node;
import org.w3c.dom.NodeList;

/**
 * An high performance and custom DOM serializer based on stax {@link XMLStreamWriter}.
 *
 * <p>
 * The serializer takes care of correctly writing empty script elements with their non empty form, because we want to ouput
 * xhtml text that will still work on html browsers.
 * </p>
 *
 * @author <a href="mailto:julien.viet@exoplatform.com">Julien Viet</a>
 * @version $Revision$
 */
public class DOMSerializer {

    /** . */
    private static final Log            log                        = ExoLogger.getLogger(DOMSerializer.class);

    /** Thread safe. */
    private static final XMLOutputFactory outputFactory;

    /** . */
    private static final String DEFAULT_XML_OUTPUT_FACTORY = "com.sun.xml.internal.stream.XMLOutputFactoryImpl";

    static {
        XMLOutputFactory tmp;
        try {
            Class<XMLOutputFactory> cl = (Class<XMLOutputFactory>) Thread.currentThread().getContextClassLoader()
                    .loadClass(DEFAULT_XML_OUTPUT_FACTORY);
            tmp = cl.newInstance();
        } catch (Exception e) {
            tmp = XMLOutputFactory.newInstance();
            log.warn("Could not instantiate " + DEFAULT_XML_OUTPUT_FACTORY + " will use default provided by runtime instead "
                    + tmp.getClass().getName());
        }

        //
        outputFactory = tmp;
    }

    public static void serialize(Element element, Writer writer) throws IOException, XMLStreamException {
        XMLStreamWriter xml = outputFactory.createXMLStreamWriter(writer);
        serialize(element, xml);
        xml.writeEndDocument();
        xml.flush();
    }

    private static void serialize(Element element, XMLStreamWriter writer) throws IOException, XMLStreamException {
        String tagName = element.getTagName();

        // Determine if empty
        // Note that we won't accumulate the elements that would be serialized for performance reason
        // we will just reiterate later before ending the element
        boolean empty;
        if (tagName.equalsIgnoreCase("script")) {
            empty = false;
        } else {
            empty = true;
            NodeList children = element.getChildNodes();
            int length = children.getLength();
            for (int i = 0; i < length && empty; i++) {
                Node child = children.item(i);
                if (child instanceof CharacterData) {
                    empty = false;
                } else if (child instanceof Element) {
                    empty = false;
                }
            }
        }

        //
        if (empty) {
            writer.writeEmptyElement(tagName);
        } else {
            writer.writeStartElement(tagName);
        }

        // Write attributes
        if (element.hasAttributes()) {
            NamedNodeMap attrs = element.getAttributes();
            int length = attrs.getLength();
            for (int i = 0; i < length; i++) {
                Attr attr = (Attr) attrs.item(i);
                writer.writeAttribute(attr.getName(), attr.getValue());
            }
        }

        //
        if (!empty) {
            // Serialize children that are worth to be
            NodeList children = element.getChildNodes();
            int length = children.getLength();
            for (int i = 0; i < length; i++) {
                Node child = children.item(i);
                if (child instanceof CDATASection) {
                    writer.writeCData(((CDATASection) child).getData());
                } else if (child instanceof CharacterData) {
                    writeTextData(writer, ((CharacterData) child).getData());
                } else if (child instanceof Element) {
                    serialize((Element) child, writer);
                }
            }

            // Close
            writer.writeEndElement();
        }
    }

    private static void writeTextData(XMLStreamWriter writer, String data) throws XMLStreamException {
        StringBuilder builder = new StringBuilder();

        for (int i = 0; i < data.length(); i++) {
            char c = data.charAt(i);
            String encodedValue = HTMLEntityEncoder.getInstance().lookupEntityName(c);

            if (encodedValue == null) {
                builder.append(c);
            } else {
                builder.append(encodedValue);
            }
        }

        writer.writeCharacters(builder.toString());
    }
}
