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();

         }

     }

 }