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"); 

	}

}