/**
 * Copyright (c) 2007-2012, JGraph Ltd
 */
package com.mxgraph.util;

import java.io.StringReader;
import java.io.StringWriter;
import java.util.logging.Level;
import java.util.logging.Logger;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.dom.DOMSource;
import javax.xml.transform.stream.StreamResult;

import org.w3c.dom.Document;
import org.w3c.dom.Node;

import org.xml.sax.InputSource;

/**
 * Contains various XML helper methods for use with mxGraph.
 */
public class mxXmlUtils
{

	private static final Logger log = Logger.getLogger(mxXmlUtils.class.getName());

	/**
	 * 
	 */
	private static DocumentBuilder documentBuilder = null;
	
	/**
	 * 
	 */
	public static DocumentBuilder getDocumentBuilder()
	{
		if (documentBuilder == null)
		{
			DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
			dbf.setExpandEntityReferences(false);
			dbf.setXIncludeAware(false);
			dbf.setValidating(false);

			try
			{
				dbf.setFeature("http://apache.org/xml/features/nonvalidating/load-external-dtd", false);
				dbf.setFeature("http://xml.org/sax/features/external-parameter-entities", false);
				dbf.setFeature("http://xml.org/sax/features/external-general-entities", false);
			}
			catch (ParserConfigurationException e)
			{
				log.log(Level.SEVERE, "Failed to set feature", e);
			}

			try
			{
				documentBuilder = dbf.newDocumentBuilder();
			}
			catch (Exception e)
			{
				log.log(Level.SEVERE, "Failed to construct a document builder", e);
			}
		}
		
		return documentBuilder;
	}
	
	/**
	 * Returns a new document for the given XML string. External entities and DTDs are ignored.
	 * 
	 * @param xml
	 *            String that represents the XML data.
	 * @return Returns a new XML document.
	 */
	public static Document parseXml(String xml)
	{
		try
		{
			return getDocumentBuilder().parse(new InputSource(new StringReader(xml)));
		}
		catch (Exception e)
		{
			log.log(Level.SEVERE, "Failed to parse XML", e);
		}
		
		return null;
	}

	/**
	 * Returns a string that represents the given node.
	 * 
	 * @param node
	 *            Node to return the XML for.
	 * @return Returns an XML string.
	 */
	public static String getXml(Node node)
	{
		try
		{
			Transformer tf = TransformerFactory.newInstance().newTransformer();

			tf.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
			tf.setOutputProperty(OutputKeys.ENCODING, "UTF-8");

			StreamResult dest = new StreamResult(new StringWriter());
			tf.transform(new DOMSource(node), dest);

			return dest.getWriter().toString();
		}
		catch (Exception e)
		{
			log.log(Level.SEVERE, "Failed to convert XML object to string", e);
		}

		return "";
	}
}
