D-Net

package eu.dnetlib.goldoa.service;

import eu.dnetlib.goldoa.domain.Currency;

import org.springframework.stereotype.Service;

import org.w3c.dom.Document;

import javax.annotation.PostConstruct;

import javax.annotation.PreDestroy;

import javax.xml.parsers.DocumentBuilder;

import javax.xml.parsers.DocumentBuilderFactory;

import javax.xml.parsers.ParserConfigurationException;

import javax.xml.xpath.XPath;

import javax.xml.xpath.XPathExpression;

import javax.xml.xpath.XPathExpressionException;

import javax.xml.xpath.XPathFactory;

import java.util.HashMap;

import java.util.Map;

import java.util.concurrent.Executors;

import java.util.concurrent.ScheduledExecutorService;

import java.util.concurrent.TimeUnit;

/*

 * Created by antleb on 5/4/15.

*/

@Service("currencyConverter")

public class CurrencyConverter {

	private ScheduledExecutorService executorService = Executors.newSingleThreadScheduledExecutor();

	private Map<Currency, Float> rateMap = new HashMap<Currency, Float>();

	@PostConstruct

	public void init() throws XPathExpressionException, ParserConfigurationException {

		executorService.scheduleAtFixedRate(new RateUpdater(), 0, 1, TimeUnit.HOURS);

	}

	@PreDestroy

	public void destroy() {

		executorService.shutdownNow();

	}

	public float convert(Currency from, Currency to, float amount) {

		float fromRate = rateMap.get(from);

		float toRate = rateMap.get(to);

		return (toRate / fromRate) * amount;

	}

	class RateUpdater implements Runnable {

		private Map<Currency, XPathExpression> xpaths = new HashMap<Currency, XPathExpression>();

		DocumentBuilder builder;

		public RateUpdater() throws ParserConfigurationException, XPathExpressionException {

			DocumentBuilderFactory factory = DocumentBuilderFactory.newInstance();

			builder = factory.newDocumentBuilder();

			XPathFactory xPathfactory = XPathFactory.newInstance();

			XPath xpath = xPathfactory.newXPath();

			for (Currency currency : Currency.values())

				if (!currency.equals(Currency.EUR))

					xpaths.put(currency, xpath.compile("//*[local-name()='Cube' and @*[local-name()='currency']='" + currency.name() + "']/@rate"));

		}

		@Override

		public void run() {

			try {

				Document doc = builder.parse("http://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml");

				rateMap.put(Currency.EUR, 1.0f);

				for (Currency currency : xpaths.keySet()) {

					String rate = xpaths.get(currency).evaluate(doc);

					if (rate != null)

						rateMap.put(currency, Float.parseFloat(rate));

				}

			} catch (Exception e) {

				e.printStackTrace();

			}

		}

	}

}