package org.mai.dep810.cer;

import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.math.BigDecimal;
import java.util.Currency;

import static org.junit.Assert.*;


public class CurrencyExchangeRateTest {
    @Before
    public void setUp() throws Exception {
    }

    @After
    public void tearDown() throws Exception {
    }

    @Test(expected = IncorrectExchangeRateException.class)
    public void convertTest() throws Exception {
        Currency usd = Currency.getInstance("USD");
        Currency gbp = Currency.getInstance("GBP");
        Currency eur = Currency.getInstance("EUR");

        Money hundredDollars = new Money(usd, new BigDecimal(100));
        Money hundredEurs = new Money(eur, new BigDecimal(100));

        CurrencyExchangeRate usdToPound = new CurrencyExchangeRate(new BigDecimal(0.75), usd, gbp);

        Money usdConvertedToPounds = usdToPound.convert(hundredDollars);

        assertEquals(usdConvertedToPounds.getCurrency(), gbp);
        assertEquals(usdConvertedToPounds.getAmount(), new BigDecimal(75).setScale(2));

        Money eurCoverted = usdToPound.convert(hundredEurs);
    }

}

package org.mai.dep810.cer;

import java.math.BigDecimal;
import java.util.Currency;

public class CurrencyExchangeRate {

    BigDecimal rate;
    Currency from;
    Currency to;

    public CurrencyExchangeRate(BigDecimal rate, Currency from, Currency to) {
        this.rate = rate;
        this.from = from;
        this.to = to;
    }

    public Money convert(Money m) {
        if(m.getCurrency().equals(from)) {
            return new Money(to, m.getAmount().multiply(rate));
        } else {
            throw new IncorrectExchangeRateException("Unable to convert currency "+m.getCurrency().getCurrencyCode() + " from "+from.getCurrencyCode());
        }
    }
}