package com.skatestown.invoice;

import java.io.File;
import org.xml.sax.Attributes;
import org.xml.sax.SAXException;
import javax.xml.parsers.SAXParser;
import javax.xml.parsers.SAXParserFactory;
import org.xml.sax.helpers.DefaultHandler;

/**
 * Check Skatestown invoice totals using a SAX parser
 */
 
 public class InvoiceCheckerSAX
   extends DefaultHandler
   implements InvoiceChecker 
   {
	   // Class-level data
	   double runningTotal = 0.0;
	   double total = 0.0; // invoice total
	   
	   // Utility for extracting amounts from content
	   boolean isMoneyContent = false;
	   double amount = 0.0;
	   
	   /**
	    * Check invoice totals
		* @param inoviceXML Invoice XML document
		* @exception Exception any exception returned during processing
		*/
		public void checkInvoice(File invoiceXML) throws Exception {
			// Use default (non-validating) parser
			SAXParserFactory factory = SAXParserFactory.newInstance();
			SAXParser saxParser = factory.newSAXParser();
			
			// Parse the input, we are the handler of SAX events
			saxParser.parse(invoiceXML, this);
		}
		
		// SAX DocumentHandler methods
		public void startDocument() throws SAXException {
			runningTotal = 0.0; 
			total = 0.0;
			isMoneyContent = false;
		}
		
		public void endDocument() throws SAXException {
			// Use delta equality to prevent cumulative binary arithmetic errors. 
			// Choose delta = 1/2 of one cent
			if (Math.abs(runningTotal - total) >= .005) {
				throw new SAXException(
				  "Invoice error: total is " + Double.toString(total) + 
				  " while our calculation shows a total of " + 
				  Double.toString(Math.round(runningTotal * 100) / 100.0));
			}
		}
		
		public void startElement(String namespaceURI, String localName, String qualifiedName,
		Attributes attrs) throws SAXException {
			if (localName.equals("item")) {
				// Find item subtotal; add it to running total
				runningTotal += Integer.valueOf(attrs.getValue(namespaceURI, "quantity")).intValue() *
				    Double.valueOf(attrs.getValue(namespaceURI, "unitPrice")).doubleValue();
			} else if (localName.equals("tax") || (localName.equals("shippingAndHandling")) ||
			(localName.equals("totalCost"))) {
				isMoneyContent = true; // prepare to extract money amount
			}
		}
		
		public void startElement(String namespaceURI, String localName, String qualifiedName) 
		    throws SAXException {
	        if (isMoneyContent) {
				if (localName.equals("totalCost")) {
					total = amount;
				} else {
					// It must be tax or shipping and handling
					runningTotal += amount;
				}
				isMoneyContent = false;
			}
		}
		
		public void characters(char buf[], int offset, int len) throws SAXException
		{
			if (isMoneyContent) {
				String value = new String(buf, offset, len);
				amount = Double.valueOf(value).doubleValue();
			}
		}
}