package org.apidesign.apifest08.currency;

 import java.io.Serializable;

 /**

  * Value class, holding an exchange rate between two currencies.

  * Designed to be an immutable.

  * 

  * @author ked

  */

 public final class ExchangeRateValue<AmountType, IdentifierType> implements Serializable {

     private final CurrencyValue<AmountType, IdentifierType> currencyA;

     private final CurrencyValue<AmountType, IdentifierType> currencyB;

     private ExchangeRateValue(

             CurrencyValue<AmountType, IdentifierType> currencyA,

             CurrencyValue<AmountType, IdentifierType> currencyB) {

         if (currencyA.getIdentifier() == null ||

             currencyB.getIdentifier() == null ||

             currencyA.getIdentifier().equals(currencyB)) {

                 throw new IllegalArgumentException("Inappropriate exchange rates' identifiers!");

         }

         this.currencyA = currencyA;

         this.currencyB = currencyB;

     }

     public CurrencyValue<AmountType, IdentifierType> getCurrencyA() {

         return currencyA;

     }

     public CurrencyValue<AmountType, IdentifierType> getCurrencyB() {

         return currencyB;

     }

     @Override

     public boolean equals(Object obj) {

         if (obj == null) {

             return false;

         }

         if (getClass() != obj.getClass()) {

             return false;

         }

         final ExchangeRateValue other = (ExchangeRateValue) obj;

         if (this.currencyA != other.currencyA && (this.currencyA == null || !this.currencyA.equals(other.currencyA))) {

             return false;

         }

         if (this.currencyB != other.currencyB && (this.currencyB == null || !this.currencyB.equals(other.currencyB))) {

             return false;

         }

         return true;

     }

     @Override

     public int hashCode() {

         int hash = 3;

         hash = 71 * hash + (this.currencyA != null ? this.currencyA.hashCode() : 0);

         hash = 71 * hash + (this.currencyB != null ? this.currencyB.hashCode() : 0);

         return hash;

     }

     /**

      * Creates new instance.

      * Generic types of the new instance are derived from types of the parameters.

      * 

      * @param <AmountType> type of the currency amount

      * @param <IdentifierType> type of the currency identifier

      * @param currencyA one currency of the exchange rate

      * @param currencyB another currency of the exchange rate

      * @return new instance

      */

     public static <AmountType, IdentifierType> ExchangeRateValue<AmountType, IdentifierType> getExchangeRate(

             CurrencyValue<AmountType, IdentifierType> currencyA,

             CurrencyValue<AmountType, IdentifierType> currencyB) {

         return new ExchangeRateValue<AmountType, IdentifierType>(currencyA, currencyB);

     }

 }