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;

	}

}