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the public API of appNG
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/*
 * Copyright 2011-2019 the original author or authors.
 *
 * 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.appng.api.support;

import java.io.IOException;
import java.io.InputStream;
import java.util.Stack;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;

import org.w3c.dom.Document;
import org.w3c.dom.Element;
import org.w3c.dom.Node;
import org.xml.sax.Attributes;
import org.xml.sax.Locator;
import org.xml.sax.SAXException;
import org.xml.sax.helpers.DefaultHandler;

/**
 * XML Reader creating a {@link Document} with line information for each node. This has been inspired by the following
 * blog post https://eyalsch.wordpress.com/2010/11/30/xml-dom-2/
 * 
 * 
 * @author Claus Stümke, aiticon GmbH, 2017
 *
 */
public class PositionalXMLReader {
	final static String LINE_NUMBER_KEY_NAME = "lineNumber";

	public static Document readXML(final InputStream is) throws IOException, SAXException {
		final Document doc;
		SAXParser parser;
		try {
			final SAXParserFactory factory = SAXParserFactory.newInstance();
			parser = factory.newSAXParser();
			final DocumentBuilderFactory docBuilderFactory = DocumentBuilderFactory.newInstance();
			final DocumentBuilder docBuilder = docBuilderFactory.newDocumentBuilder();
			doc = docBuilder.newDocument();
		} catch (final ParserConfigurationException e) {
			throw new RuntimeException("Can't create SAX parser / DOM builder.", e);
		}

		final Stack elementStack = new Stack();
		final StringBuilder textBuffer = new StringBuilder();
		final DefaultHandler handler = new DefaultHandler() {
			private Locator locator;

			@Override
			public void setDocumentLocator(final Locator locator) {
				this.locator = locator; // Save the locator, so that it can be used later for line tracking when
										// traversing nodes.
			}

			@Override
			public void startElement(final String uri, final String localName, final String qName,
					final Attributes attributes) throws SAXException {
				addTextIfNeeded();
				final Element el = doc.createElement(qName);
				el.setUserData(LINE_NUMBER_KEY_NAME, Integer.valueOf(this.locator.getLineNumber()), null);
				for (int i = 0; i < attributes.getLength(); i++) {
					el.setAttribute(attributes.getQName(i), attributes.getValue(i));
				}
				elementStack.push(el);
			}

			@Override
			public void endElement(final String uri, final String localName, final String qName) {
				addTextIfNeeded();
				final Element closedEl = elementStack.pop();
				if (elementStack.isEmpty()) { // Is this the root element?
					doc.appendChild(closedEl);
				} else {
					final Element parentEl = elementStack.peek();
					parentEl.appendChild(closedEl);
				}
			}

			@Override
			public void characters(final char ch[], final int start, final int length) throws SAXException {
				textBuffer.append(ch, start, length);
			}

			// Outputs text accumulated under the current node
			private void addTextIfNeeded() {
				if (textBuffer.length() > 0) {
					final Element el = elementStack.peek();
					final Node textNode = doc.createTextNode(textBuffer.toString());
					el.appendChild(textNode);
					textBuffer.delete(0, textBuffer.length());
				}
			}
		};
		parser.parse(is, handler);

		return doc;
	}
}