package org.apidesign.apifest08.currency;

 import java.util.*;

 final class ConstantRateConverter implements CurrencyConverter {

 	private final Currency from;

 	private final Currency to;

 	private final double rate;

 	public ConstantRateConverter(Currency from, Currency to, double rate) throws IllegalArgumentException {

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

 			throw new NullPointerException("None of the currencies can be null");

 		if (from.equals(to))

 			throw new IllegalArgumentException("Cannot create converter with two equal currencies");

 		this.from = from;

 		this.to = to;

 		this.rate = rate;

 	}

 	@Override

 	public double convert(double value, String from, String to)

 			throws CurrencyConversionException, NullPointerException {

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

 	}

 	@Override

 	public double convert(double value, Currency from, Currency to)

 			throws NullPointerException, CurrencyConversionException {

 		if (this.from.equals(from)) {

 			if (!this.to.equals(to))

 				throw new CurrencyConversionException(from, to, "Unsupported currency");

 			return value * rate;

 		}

 		if (this.from.equals(to)) {

 			if (!this.to.equals(from))

 				throw new CurrencyConversionException(from, to, "Unsupported currency");

 			return value / rate;

 		}

 		throw new CurrencyConversionException(from, to, "Unsupported currency"); 

 	}

 }