package org.apidesign.apifest08.currency;

import java.math.BigDecimal;

import java.util.Currency;

import java.util.HashMap;

import java.util.Map;

import java.util.Timer;

import java.util.TimerTask;

/**

 * Keeps track of the current value for each currency as USD.  

 * 

 * @author D'Arcy Smith

 * @version 1.0

 */

class CurrencyValues

{

    /**

     * The values expressed in USD.

     */

    private static Map<Currency, BigDecimal> values;

    /**

     * Update the values periodically

     */

    private static final Timer refresher;

    static

    {

        final Refresher refresherTask;

        final long delay;

        // load the map NOW! (don't use the scheduler to do it just because we want

        // to be 100% certain it is loaded before anything else can be called.

        refresh();

        refresherTask = new Refresher();

        refresher = new Timer("CurrencyValues Refresher", true);

        // update once an hour

        delay = 1000 * 60 * 60;

        refresher.scheduleAtFixedRate(refresherTask, delay, delay);

    }

    /**

     * Prevent accidental creation.

     */

    private CurrencyValues()

    {

    }

    /**

     * Refresh the currency values.

     */

    static void refresh()

    {

        Map<Currency, BigDecimal> newValues;    

        Currency                  currency;

        newValues = new HashMap<Currency, BigDecimal>();

        // these would update from a data source, database, web service, something...

        currency = Currency.getInstance("USD");

        newValues.put(currency, BigDecimal.valueOf(1.0).setScale(2));

        currency = Currency.getInstance("CZK");

        newValues.put(currency, BigDecimal.valueOf(17.0));

        currency = Currency.getInstance("SKK");

        newValues.put(currency, BigDecimal.valueOf(21.25));

        // don't sycnhronize all of it because clients can use slightly out of

        // date information.

        synchronized(CurrencyValues.class)

        {

            values = newValues;

        }

    }

    /**

     * Get the value of the specified currency in USD.

     * 

     * @param currency the corrency to get.

     * @return the value of the currency in USD.

     * @throws IllegalArgumentException if currency is null.

     */

    static BigDecimal getValue(final Currency currency)

    {

        final BigDecimal value;

        if(currency == null)

        {

            throw new IllegalArgumentException("currencyName cannot be null");

        }

        // make sure we are not updating the map right now

        synchronized(CurrencyValues.class)

        {

            value = values.get(currency);

        }

        return (value);

    }

    /**

     * Used to update the currency map periodically.

     */

    private static class Refresher

        extends TimerTask

    {

        /**

         * call the refresh method.

         */

        @Override

        public void run() 

        {

            refresh();

        }

    }

}