package org.apidesign.apifest08.currency;

 import java.math.BigDecimal;

 import java.util.Currency;

 /**

  * The exchange rate between two currencies.

  *

  * @author D'Arcy Smith

  * @version 1.0

  */

 public final class ExchangeRate

 {

     /**

      * 

      */

     private final Currency currencyA;

     /**

      * 

      */

     private final Currency currencyB;

     /**

      * 

      */

     private final BigDecimal rateAtoB;

     /**

      * 

      */

     private final BigDecimal rateBtoA;

     /**

      * Construct an ExchangeRate with the specified values.

      * 

      * @param a the first currency

      * @param b the second currency

      * @param ra the rate to convert a to b

      * @param rb the rate to covertt b to a

      * @throws IllegalArgumentException if any parameter is null.

      */

     public ExchangeRate(final Currency   a,

                         final Currency   b,

                         final BigDecimal ra,

                         final BigDecimal rb)

     {

         if(a == null)

         {

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

         }

         if(b == null)

         {

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

         }

         if(ra == null)

         {

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

         }

         if(rb == null)

         {

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

         }

         if(ra.compareTo(BigDecimal.ZERO) <= 0)

         {

             throw new IllegalArgumentException("ra cannot be <= 0, was: " + ra);

         }

         if(rb.compareTo(BigDecimal.ZERO) <= 0)

         {

             throw new IllegalArgumentException("rb cannot be <= 0, was: " + ra);

         }

         currencyA = a;

         currencyB = b;

         rateAtoB  = ra;

         rateBtoA  = rb;

     }

     /**

      * Get the first currency.

      * 

      * @return the first currency.

      */

     public Currency getCurrencyA()

     {

         return currencyA;

     }

     /**

      * Get the second currency.

      * 

      * @return the second currency.

      */

     public Currency getCurrencyB()

     {

         return currencyB;

     }

     /**

      * Get the conversion rate from currencyA to currencyB.

      * 

      * @return the conversion rate from currencyA to currencyB.

      */

     public BigDecimal getRateAtoB()

     {

         return rateAtoB;

     }

     /**

      * Get the conversion rate from currencyB to currencyA.

      * 

      * @return the conversion rate from currencyB to currencyA.

      */

     public BigDecimal getRateBtoA()

     {

         return rateBtoA;

     }

 }