import java.util.*;
import java.io.*;
import java.sql.Timestamp;
import org.w3c.dom.*;

/**
 * The WeatherExtractor class extracts weather information from
 * a web page and saves it in XML format. If a weather XML file
 * all ready exists, the data is merged with that file, otherwise
 * a new XML data file is created
 */

public class WeatherExtractor {
	
	// The location of the various resources and files
	private static final String source = 
		"http://weather.yahoo.com/forecast/Seattle_WA_US_f.html";
	private static final String xslFile = "weather.xsl";
	private static final String xmlFile = "result.xml";
	
	public static void main(String args[]) {
		try {
			// Retrieve the source document as XML
			Document xhtml = XMLHelper.tidyHTML(source);
			// Parse the XSL document
			Document xsl   = XMLHelper.parseXMLFromFile(xslFile);
			// Get the current data by applying the XSL transform
			Document data  = XMLHelper.transformXML(xhtml, xsl);
			// For convenience, add a timestamp to what we have done
			Date now = new Date();
			Timestamp time = new Timestamp(now.getTime());
			Element root = data.getDocumentElement();
			NodeList nl = root.getElementsByTagName("WEATHER");
			Element weather = (Element)nl.item(0);
			weather.setAttribute("Retreived",time.toString());
			// Write the output file, merging if necessary
			File dataFile  = new File(xmlFile);
			if (dataFile.exists()) {
				// If we have extracted before, merge the data and write the file
				Document oldData = XMLHelper.parseXMLFromFile(dataFile);
				XMLHelper.mergeXML(oldData.getDocumentElement(), weather, false);
				XMLHelper.outputXMLToFile(oldData, xmlFile);
			} else {
				// If this is our first extraction, just write the file
				XMLHelper.outputXMLToFile(data, xmlFile);
			}
		} catch (XMLHelperException xmlhe) {
			System.err.println(
				"There was an error in the extraction process:\n" + 
				xmlhe.getMessage());
		}
	}
}