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;

 	}

 }