japod@6: package org.apidesign.apifest08.currency;
japod@6: 
japod@21: import static org.apidesign.apifest08.currency.Assert.notNull;
japod@21: 
japod@6: import java.math.BigDecimal;
japod@21: import java.math.RoundingMode;
japod@38: import java.util.ArrayList;
japod@6: import java.util.Currency;
japod@38: import java.util.List;
japod@6: 
japod@52: /**
japod@52:  * Currency covertor.
japod@52:  */
japod@21: public final class Convertor {
japod@6: 	
japod@38: 	private List<ConvertorDelegate> convertorDelegates = new ArrayList<ConvertorDelegate>();
japod@21: 	
japod@38: 	
japod@38: 	/**
japod@38: 	 * Create new instance of the converter for the given currencies and its rate.
japod@38: 	 * 
japod@38: 	 * @param rateValue the rate between the first and the second currency
japod@38: 	 * @param currencyFirst the first currency
japod@38: 	 * @param currencySecond the second currency
japod@38: 	 */
japod@21: 	public Convertor(BigDecimal rateValue, Currency currencyFirst, Currency currencySecond) {
japod@21: 		notNull(currencyFirst, "currencyFirst");
japod@21: 		notNull(currencySecond, "currencySecond");		
japod@38: 		notNull(rateValue, "rateValue");	
japod@52: 		convertorDelegates.add(new ConvertorDelegate(new StaticRateProvider(rateValue), currencyFirst, currencySecond));
japod@52: 	}
japod@52: 	
japod@52: 	/**
japod@52: 	 * Create new instance of the converter for the given currencies and its rate. 
japod@52: 	 * A rate value is provided by {@link RateProvider}.
japod@52: 	 * 
japod@52: 	 * @param rateProvider the rate provider
japod@52: 	 * @param currencyFirst the first currency
japod@52: 	 * @param currencySecond the second currency
japod@52: 	 */
japod@52: 	public Convertor(RateProvider rateProvider, Currency currencyFirst, Currency currencySecond) {
japod@52: 		notNull(currencyFirst, "currencyFirst");
japod@52: 		notNull(currencySecond, "currencySecond");		
japod@52: 		notNull(rateProvider, "rateProvider");
japod@52: 		convertorDelegates.add(new ConvertorDelegate(rateProvider, currencyFirst, currencySecond));
japod@38: 	}
japod@38: 	
japod@38: 	/**
japod@38: 	 * Create new instance of the convertor from the given convertors. 
japod@38: 	 * @param convertors the convertors
japod@38: 	 */
japod@38: 	public Convertor(Convertor... convertors) {
japod@38: 		notNull(convertors, "convertors");
japod@38: 		if(convertors.length == 0) {
japod@38: 			throw new IllegalArgumentException("There must be at least one converter.");
japod@38: 		}
japod@21: 		
japod@38: 		for(Convertor convertor: convertors) {
japod@38: 			if(convertor != null) {
japod@38: 				convertorDelegates.addAll(convertor.convertorDelegates);
japod@38: 			}
japod@38: 		}
japod@21: 	}
japod@21:     	
japod@6: 	/**
japod@21: 	 * Converts an amount value between the two currencies of this converter.
japod@6: 	 *  
japod@6: 	 * @param amount an amount
japod@6: 	 * @param fromCurrency an amount currency
japod@6: 	 * @param toCurrency to a target currency
japod@6: 	 * @return a converted amount value
japod@6: 	 * 
japod@6: 	 * @throws ConversionException if the conversion fails
japod@6: 	 * @throws UnsupportedConversionException if the conversion between a given currencies is not supported.
japod@6: 	 */
japod@21: 	public Amount convert(BigDecimal amount, Currency fromCurrency, Currency toCurrency) throws ConversionException {
japod@21: 		notNull(amount, "amount");
japod@21: 		notNull(fromCurrency, "fromCurrency");
japod@21: 		notNull(toCurrency, "toCurrency");
japod@38: 		ConvertorDelegate appropriateDelegate = null;
japod@21: 		
japod@38: 		//try find an appropriate delegate for conversion
japod@38: 		for(ConvertorDelegate delegate : convertorDelegates) {
japod@38: 			if(delegate.isConversionSupported(fromCurrency, toCurrency)) {
japod@38: 				appropriateDelegate = delegate;
japod@38: 				break;
japod@38: 			}
japod@38: 		}
japod@38: 		
japod@38: 		if(appropriateDelegate == null) {
japod@21: 			throw new UnsupportedConversionException(fromCurrency, toCurrency);
japod@38: 		}
japod@38: 		
japod@38: 		return appropriateDelegate.convert(amount, fromCurrency, toCurrency);	
japod@21: 	}
japod@21: 	
japod@38: 	/**
japod@38: 	 * Internal delegate implements a logic for conversion between two currencies
japod@38: 	 * and vice versa.
japod@38: 	 * @see #isConversionSupported(Currency, Currency)
japod@38: 	 */
japod@38: 	private static class ConvertorDelegate {
japod@38: 		private final Currency first;
japod@38: 		private final Currency second;
japod@52: 		private final RateProvider rateProvider;
japod@38: 		public static final BigDecimal one = new BigDecimal(1);
japod@21: 		
japod@52: 		
japod@52: 		private ConvertorDelegate(RateProvider rateProvider, Currency currencyFirst, Currency currencySecond) {
japod@52: 			this.rateProvider = rateProvider;
japod@38: 			this.first = currencyFirst;
japod@38: 			this.second = currencySecond;
japod@21: 		}
japod@21: 		
japod@38: 		private Amount convert(BigDecimal amount, Currency fromCurrency, Currency toCurrency) throws ConversionException {
japod@38: 			BigDecimal rateValue = getRateValue(fromCurrency, toCurrency);
japod@38: 			BigDecimal result = rateValue.multiply(amount);			
japod@38: 			return new Amount(result, toCurrency);	
japod@38: 		}
japod@38: 		
japod@38: 		private BigDecimal getRateValue(Currency fromCurrency, Currency toCurrency) {		
japod@38: 			
japod@38: 			BigDecimal retVal;
japod@38: 			
japod@38: 			if(first == fromCurrency) {
japod@52: 				BigDecimal rateValue = rateProvider.getRate();
japod@52: 				if(rateValue == null) {
japod@52: 					throw new NullPointerException("Rate cannot be null!");
japod@52: 				}
japod@38: 				retVal = rateValue;
japod@38: 			} else {	
japod@52: 				BigDecimal rateValue = rateProvider.getRate();
japod@52: 				if(rateValue == null) {
japod@52: 					throw new NullPointerException("Rate cannot be null!");
japod@52: 				}
japod@38: 				//reverse rate	
japod@38: 				retVal = one.divide(rateValue, 10 ,RoundingMode.HALF_UP);
japod@38: 			}
japod@38: 			
japod@38: 			return retVal;
japod@38: 		}
japod@38: 		
japod@38: 		/**
japod@38: 		 * @return <code>true</code> if the delegate is able to convert from the given currency
japod@38: 		 * to the given currency and vice versa otherwise <code>false</code>.
japod@38: 		 */
japod@38: 		private boolean isConversionSupported(Currency fromCurrency, Currency toCurrency) {
japod@38: 			return ((fromCurrency == first || fromCurrency == second) && (toCurrency == first || toCurrency == second));
japod@38: 		}
japod@21: 	}
japod@52: 	
japod@52: 	/**
japod@52: 	 * A rate provider. This class represents a way how could be "static" convertor
japod@52: 	 * extended in order converts according to current rate.
japod@52: 	 */
japod@52: 	public static abstract class RateProvider { 
japod@52: 		
japod@52: 		/**
japod@52: 		 * @return a rate between the from currency and the to currency associated with
japod@52: 		 * a given convertor.
japod@52: 		 */
japod@52: 		public abstract BigDecimal getRate();
japod@52: 	}
japod@52: 	
japod@52: 	private static class StaticRateProvider extends RateProvider{
japod@52: 		private final BigDecimal rateValue;
japod@52: 		
japod@52: 		private StaticRateProvider(BigDecimal rateValue){
japod@52: 			this.rateValue = rateValue;
japod@52: 		}
japod@52: 		
japod@52: 		public BigDecimal getRate() {
japod@52: 			return this.rateValue;
japod@52: 		}
japod@52: 	}
japod@6: }