package org.apidesign.apifest08.currency;

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

 import java.math.BigDecimal;

 import java.math.RoundingMode;

 import java.util.ArrayList;

 import java.util.Currency;

 import java.util.List;

 /**

  * Currency covertor.

  */

 public final class Convertor {

 	private List<ConvertorDelegate> convertorDelegates = new ArrayList<ConvertorDelegate>();

 	/**

 	 * Create new instance of the converter for the given currencies and its rate.

 	 * 

 	 * @param rateValue the rate between the first and the second currency

 	 * @param currencyFirst the first currency

 	 * @param currencySecond the second currency

 	 */

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

 		notNull(currencyFirst, "currencyFirst");

 		notNull(currencySecond, "currencySecond");		

 		notNull(rateValue, "rateValue");	

 		convertorDelegates.add(new ConvertorDelegate(new StaticRateProvider(rateValue), currencyFirst, currencySecond));

 	}

 	/**

 	 * Create new instance of the converter for the given currencies and its rate. 

 	 * A rate value is provided by {@link RateProvider}.

 	 * 

 	 * @param rateProvider the rate provider

 	 * @param currencyFirst the first currency

 	 * @param currencySecond the second currency

 	 */

 	public Convertor(RateProvider rateProvider, Currency currencyFirst, Currency currencySecond) {

 		notNull(currencyFirst, "currencyFirst");

 		notNull(currencySecond, "currencySecond");		

 		notNull(rateProvider, "rateProvider");

 		convertorDelegates.add(new ConvertorDelegate(rateProvider, currencyFirst, currencySecond));

 	}

 	/**

 	 * Create new instance of the convertor from the given convertors. 

 	 * @param convertors the convertors

 	 */

 	public Convertor(Convertor... convertors) {

 		notNull(convertors, "convertors");

 		if(convertors.length == 0) {

 			throw new IllegalArgumentException("There must be at least one converter.");

 		}

 		for(Convertor convertor: convertors) {

 			if(convertor != null) {

 				convertorDelegates.addAll(convertor.convertorDelegates);

 			}

 		}

 	}

 	/**

 	 * 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");

 		ConvertorDelegate appropriateDelegate = null;

 		//try find an appropriate delegate for conversion

 		for(ConvertorDelegate delegate : convertorDelegates) {

 			if(delegate.isConversionSupported(fromCurrency, toCurrency)) {

 				appropriateDelegate = delegate;

 				break;

 			}

 		}

 		if(appropriateDelegate == null) {

 			throw new UnsupportedConversionException(fromCurrency, toCurrency);

 		}

 		return appropriateDelegate.convert(amount, fromCurrency, toCurrency);	

 	}

 	/**

 	 * Internal delegate implements a logic for conversion between two currencies

 	 * and vice versa.

 	 * @see #isConversionSupported(Currency, Currency)

 	 */

 	private static class ConvertorDelegate {

 		private final Currency first;

 		private final Currency second;

 		private final RateProvider rateProvider;

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

 		private ConvertorDelegate(RateProvider rateProvider, Currency currencyFirst, Currency currencySecond) {

 			this.rateProvider = rateProvider;

 			this.first = currencyFirst;

 			this.second = currencySecond;

 		}

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

 			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) {

 				BigDecimal rateValue = rateProvider.getRate();

 				if(rateValue == null) {

 					throw new NullPointerException("Rate cannot be null!");

 				}

 				retVal = rateValue;

 			} else {	

 				BigDecimal rateValue = rateProvider.getRate();

 				if(rateValue == null) {

 					throw new NullPointerException("Rate cannot be null!");

 				}

 				//reverse rate	

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

 			}

 			return retVal;

 		}

 		/**

 		 * @return <code>true</code> if the delegate is able to convert from the given currency

 		 * to the given currency and vice versa otherwise <code>false</code>.

 		 */

 		private boolean isConversionSupported(Currency fromCurrency, Currency toCurrency) {

 			return ((fromCurrency == first || fromCurrency == second) && (toCurrency == first || toCurrency == second));

 		}

 	}

 	/**

 	 * A rate provider. This class represents a way how could be "static" convertor

 	 * extended in order converts according to current rate.

 	 */

 	public static abstract class RateProvider { 

 		/**

 		 * @return a rate between the from currency and the to currency associated with

 		 * a given convertor.

 		 */

 		public abstract BigDecimal getRate();

 	}

 	private static class StaticRateProvider extends RateProvider{

 		private final BigDecimal rateValue;

 		private StaticRateProvider(BigDecimal rateValue){

 			this.rateValue = rateValue;

 		}

 		public BigDecimal getRate() {

 			return this.rateValue;

 		}

 	}

 }