package org.apidesign.apifest08.currency;

 /**

  * ConvetorImpl it the basic implementaion of Convertor interface.

  * @see Convertor Convertor for more details.

  * The 100 pences makes 1 amount of the currency.

  *

  * @author jindra

  */

 final class ConvertorImpl implements Convertor {

     private static final double P_TO_AM = 100;

     private double exchangeRate;

     ConvertorImpl(double exchangeRate) {

         this.exchangeRate = exchangeRate;

     }

     public Amount convert(Amount amount) {

         verifyInput(amount);

         double result = convertToDouble(amount) * exchangeRate;

         return convertToAmount(result);

     }

     public Amount convertBack(Amount amount) {

         if (amount == null) {

             throw new IllegalArgumentException("Amount must be not null");

         }

         double result = convertToDouble(amount) / exchangeRate;

         return convertToAmount(result);

     }

     private double convertToDouble(Amount amount) {

         double am = amount.getAmount();

         double pc = amount.getPence();

         return am + (pc / P_TO_AM);

     }

     private Amount convertToAmount(double result) {

         long resultAm = Math.round(Math.floor(result));

         long resultPc = Math.round(Math.floor((result * P_TO_AM - resultAm * P_TO_AM)));

         return new Amount(resultAm, resultPc);

     }

     private void verifyInput(Amount amount) {

         if (amount == null) {

             throw new IllegalArgumentException("Amount must be not null");

         }

         if (amount.getPence() < 0) {

             throw new IllegalArgumentException("Pences must not be negative");

         }

         if (amount.getPence() > P_TO_AM) {

             throw new IllegalArgumentException("Pences must not be over P_TO_AM");

         }

     }

 }