package org.apidesign.apifest08.currency;

 import java.util.*;

 final class MultiCurrencyConstantRateConverter implements CurrencyConverter {

 	private final Map<Currency, Double> rates;

 	public MultiCurrencyConstantRateConverter(Map<Currency, Double> rates) {

 		this.rates = rates;

 	}

 	/**

 	 * This is convenience method for convert(Currency.getInstance(from), Currency.getInstance(to)).

 	 *

 	 * @param value that should be converted form one currency to the other

 	 * @param from  ISO-4217 code of the currency of the value provided

 	 * @param to	ISO-4212 code of the currency to which the value should be converted

 	 *

 	 * @return value expressed in the target value

 	 *

 	 * @throws IllegalArgumentException if any of the arguments is not a valid ISO code

 	 * @throws CurrencyConversionException

 	 *                                  if the conversion cannot be performed with desired parameters, for

 	 *                                  example the exchange rates are not current, connection to exchange rates

 	 *                                  provider is not available

 	 * @throws NullPointerException	 if any of the specified currency ISO codes is null

 	 */

 	// this method is provided to ensure future compatibility for converters supporting more than 2 currencies

 	//		- simpler methods with fewer arguments would make using such converters less intuitive

 	@Override

 	public double convert(double value, /*@NotNull*/ String from, /*@NotNull*/ String to)

 			throws CurrencyConversionException, NullPointerException, IllegalArgumentException {

 		return convert(value, Currency.getInstance(from), Currency.getInstance(to));

 	}

 	/**

 	 * Converts the specified value from one currency (from) to target currency (to).

 	 *

 	 * @param value that should be converted form one currency to the other

 	 * @param from  ISO-4217 code of the currency of the value provided

 	 * @param to	ISO-4212 code of the currency to which the value should be converted

 	 *

 	 * @return value expressed in the target value

 	 *

 	 * @throws IllegalArgumentException if any of the arguments is not a valid ISO code

 	 * @throws CurrencyConversionException

 	 *                                  if the conversion cannot be performed with desired parameters, for

 	 *                                  example the exchange rates are not current, connection to exchange rates

 	 *                                  provider is not available

 	 * @throws NullPointerException	 if any of the specified currency ISO codes is null

 	 */

 	@Override

 	public double convert(double value, /*@NotNull*/ Currency from, /*@NotNull*/ Currency to)

 			throws CurrencyConversionException, NullPointerException {

 		// this is not necessary, but we let users know that nulls are not allowed here - should be handled by annotations

 		if (from == null || to == null)

 			throw new NullPointerException("One of the specified currencies in null");

 		Double fromRate = rates.get(from);

 		Double toRate = rates.get(to);

 		if (fromRate == null)

 			throw new CurrencyConversionException(from, to, String.format("Currency %1$s not supported", from));

 		if (toRate == null)

 			throw new CurrencyConversionException(from, to, String.format("Currency %1$s not supported", to));

 		return (value / fromRate) * toRate;

 	}

 }