package org.apidesign.apifest08.currency;

 import java.math.BigDecimal;

 import java.util.Currency;

 import java.util.Set;

 /**

  * A Convertor that looks up the exchange rate with each call to "convert".

  *

  * @author D'Arcy Smith

  * @version 1.0

  */

 public class OnlineConvertor

     implements Convertor

 {

     /**

      * The currency to convert from.

      */

     private final Currency currencyA;

     /**

      * The currency to convert to.

      */

     private final Currency currencyB;

     /**

      * Used to find the current exchange rate.

      */

     private final ExchangeRateFinder finder;

     /**

      * The convertor to perform the conversion.

      */

     private Convertor realConvertor;

     /**

      * Constructs an OnlinConvertor with the specified currencies.

      * 

      * @param a the currency to convert from.

      * @param b the currency to convert to.

      * @param f the finder used to obtanin the current exchange rate.

      * @throws IllegalArgumentException if either a or b are null.

      */

     public OnlineConvertor(final Currency           a,

                            final Currency           b,

                            final ExchangeRateFinder f)

     {

         if(a == null)        

         {

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

         }

         if(b == null)

         {

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

         }

         if(f == null)

         {

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

         }

         currencyA     = a;

         currencyB     = b;

         finder        = f;

         realConvertor = lookupRate();

     }

     /**

      * Convert an amount from one currency to another.  Before the conversion takes place 

      * the current exchange rate is looked up.

      *

      * @param from the currency to convert from.

      * @param to the currency to convert to.

      * @param amount the amount to convert.

      * @return the converted amount.

      * @throws IllegalArgumentException if any of the arguments are null.

      * @throws InvalidConversionException if either from or to are not equal to the currencies passed to the constructor.

      */

     public BigDecimal convert(final Currency   from, 

                               final Currency   to, 

                               final BigDecimal amount) 

         throws InvalidConversionException

     {

         final BigDecimal value;

         synchronized(this)

         {

             realConvertor = lookupRate();

             value         = realConvertor.convert(from, to, amount);

         }

         return (value);

     }

     /**

      * Lookup the current exchange rate.

      * 

      * @return

      */

     private final Convertor lookupRate()

     {

         final Convertor convertor;

         final ExchangeRate rate;

         rate      = finder.findRate(currencyA, currencyB);

         convertor = ConvertorFactory.getConvertor(rate.getCurrencyA(), rate.getRateAtoB(), rate.getCurrencyB(), rate.getRateBtoA());

         return (convertor);

     }

     /**

      * Check to see if converting between the two currencies is possible.

      * 

      * @param from the currency to convert from.

      * @param to the currency to convert to.

      * @return true if the conversion is possible.

      * @throws IllegalArgumentException if either from or to are null.

      */

     public boolean canConvert(final Currency from, 

                               final Currency to) 

     {

         if(from == null)

         {

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

         }

         if(to == null)

         {

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

         }

         return (realConvertor.canConvert(from, to));

     }

     /**

      * Get the currencies that the convertor supports.

      * 

      * @return the supported currencies.

      */

     public Set<Currency> getCurrencies() 

     {

         return (realConvertor.getCurrencies());

     }

     /**

      * Get the conversion rate between two currencies.  This does not lookup the current

      * conversion rate (it probably should, but given the way the contest works that might 

      * not be a good idea - if it were the real world way it might be a good idea).

      * 

      * @param from the currency to convert from.

      * @param to the currency to convert to.

      * @return the conversion rate between the two currencies.

      * @throws InvalidConversionException if canConvert would return false.

      * @throws IllegalArgumentException if either from or to are null.

      */

     public BigDecimal getConversionRate(final Currency from, 

                                         final Currency to) 

         throws InvalidConversionException 

     {        

         if(from == null)

         {

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

         }

         if(to == null)

         {

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

         }

         return (realConvertor.getConversionRate(from, to));

     }    

 }