package org.apidesign.apifest08.currency;

import static org.apidesign.apifest08.currency.Assert.notNull;

import java.math.BigDecimal;

import java.math.RoundingMode;

import java.util.Currency;

public final class Convertor {

	private final Currency first;

	private final Currency second;

	private final BigDecimal rateValue; // a rate between the first currency and the second currency

	public static final BigDecimal one = new BigDecimal(1);	

	public Convertor(BigDecimal rateValue, Currency currencyFirst, Currency currencySecond) {

		notNull(currencyFirst, "currencyFirst");

		notNull(currencySecond, "currencySecond");		

		notNull(rateValue, "rateValue");

		this.rateValue = rateValue;

		this.first = currencyFirst;

		this.second = currencySecond;

	}

	/**

	 * Converts an amount value between the two currencies of this converter.

	 *  

	 * @param amount an amount

	 * @param fromCurrency an amount currency

	 * @param toCurrency to a target currency

	 * @return a converted amount value

	 * 

	 * @throws ConversionException if the conversion fails

	 * @throws UnsupportedConversionException if the conversion between a given currencies is not supported.

	 */

	public Amount convert(BigDecimal amount, Currency fromCurrency, Currency toCurrency) throws ConversionException {

		notNull(amount, "amount");

		notNull(fromCurrency, "fromCurrency");

		notNull(toCurrency, "toCurrency");

		if((fromCurrency != first && fromCurrency != second) || (toCurrency != first && toCurrency != second)) {

			throw new UnsupportedConversionException(fromCurrency, toCurrency);

		}		

		BigDecimal rateValue = getRateValue(fromCurrency, toCurrency);

		BigDecimal result = rateValue.multiply(amount);			

		return new Amount(result, toCurrency);	

	}

	private BigDecimal getRateValue(Currency fromCurrency, Currency toCurrency) {		

		BigDecimal retVal;

		if(first == fromCurrency) {

			retVal = rateValue;

		} else {	

			//reverse rate	

			retVal = one.divide(rateValue, 10 ,RoundingMode.HALF_UP);

		}

		return retVal;

	}

}