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");

        }

    }

}