D-Net

package eu.dnetlib.goldoa.service;

import eu.dnetlib.goldoa.domain.Currency;

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.

 */

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();

            }

        }

    }

}