diff -r f6073056b9fe -r a7e6f84fb078 task2/solution13/src/org/apidesign/apifest08/currency/Convertor.java
--- a/task2/solution13/src/org/apidesign/apifest08/currency/Convertor.java	Wed Oct 01 10:43:05 2008 +0200
+++ b/task2/solution13/src/org/apidesign/apifest08/currency/Convertor.java	Tue Oct 07 01:18:23 2008 +0200
@@ -5,23 +5,54 @@
 import java.math.RoundingMode;
 
 /** Convertor able to convert amount from one currency to other currency.
+ * <p>
+ * Conversion method are:
+ * <ul>
+ * <li>{@link #convert(ConvertorCurrency, ConvertorCurrency, BigDecimal)} - convert using exchange rate specified in exchange rate provide. <em>Do not try use reverted excahnage rate</em>. 
+ * <li>{@link #convertWithReversibleRates(ConvertorCurrency, ConvertorCurrency, BigDecimal)} - convert using exchange rate specified in exchange rate provide. <em>Try use reverted excahnage rate</em>. 
+ * </ul>
  * 
  * Exchange rate is provided by {@link ExchangeRateProvider}.
  */
 public class Convertor {
-    boolean remainderAllowed = false; //if false, remained is not allowed (should be true ideally, but can't handle it now)
+    private Convertor[] convertors;
+
+    /** Create new <code>Convertor</code> as merge of provided convertors. Merged convertor will use
+     * provided convertors to convert between currencies.
+     * <p>
+     * Only one should be able to provide conversion between currencies. If more than one convertos
+     * are able to convert currency, one of conversions will be used (it is not defined which).
+     * 
+     * @since version 2
+     * @param convertors Convertor used to create merge-convertor.
+     * @return Returns new convertor instance.
+     */
+    public static Convertor createConvertorAsMerge(Convertor[] convertors) {
+        return new Convertor(convertors);
+    }
+    
+    boolean remainderAllowed = true; //if false, remained is not allowed (should be true ideally, but can't handle it now)
     ExchangeRateProvider exchangeRateProvider; 
     
+    /** Create simle convertor.
+     */
     private Convertor() {
-        
+        this.convertors=new Convertor[0];
+    }
+    
+    /** Create merge convertor.
+     */            
+    private Convertor(Convertor[] convertors) {
+        this.convertors = convertors;       
     }
     
     /**
-     * Static method used to create convertor.
+     * Create new <code>Convertor</code> using <code>ExchangeRateProvider</code>.
      * 
      * @param exchangeRateProvider {@link ExchangeRateProvider} used to get exchange rate.
      * 
      * @return Returns <code>Convertor</code> which can be used to convert money.
+     * @since version1
      */
     public static Convertor createConvertor(ExchangeRateProvider exchangeRateProvider) {
         Convertor c = new Convertor();
@@ -36,9 +67,11 @@
      * 
      * @param amount Amount which should be converted. Can't be negative value (can be zero or positive).
      * @return Return <code>ConversionResult</code> which holds conversion result.
+     * @since version1
+     * @deprecated since version2. Use {@link #convert(ConvertorCurrency, ConvertorCurrency, BigDecimal) } - explicitly specify conversion currencies.
      */
     public ConversionResult convert(BigDecimal amount) {
-        return convertValue(amount, false);
+        return convertValue(exchangeRateProvider.getFromCurrency(), exchangeRateProvider.getToCurrency(),amount, false,false);
     }
     
     /**
@@ -47,32 +80,44 @@
      * 
      * @param amount Amount which should be converted. Can't be negative value (can be zero or positive).
      * @return Return <code>ConversionResult</code> which holds conversion result.
+     * @since version1
+     * @deprecated since version2. Use {@link #convert(ConvertorCurrency, ConvertorCurrency, BigDecimal) } - explicitly specify conversion currencies.
      */
     public ConversionResult convertBack(BigDecimal amount) {
-        return convertValue(amount, true);
+        return convertValue(exchangeRateProvider.getFromCurrency(), exchangeRateProvider.getToCurrency(),amount, true,false);
     }
 
-    private ConversionResult convertValue(BigDecimal amount, boolean convertBack) throws RuntimeException {
+    private ConversionResult convertUsingSimpleConvertor(ConvertorCurrency fromCurrency, ConvertorCurrency toCurrency, boolean reversibleExRate, BigDecimal amount, boolean convertBack) throws ConversionNotSupportedException, RuntimeException {
         ConversionResult result = new ConversionResult();
-        
-        ExchangeRate rate = exchangeRateProvider.getExchangeRate();
-        int fromFranctionDigits = exchangeRateProvider.getFromCurrency().getDefaultFractionDigits();
-        int toFractionDigits = exchangeRateProvider.getToCurrency().getDefaultFractionDigits();
-         
-        if (toFractionDigits!=2) {
-            throw new RuntimeException("Can't process currency with defaultFractionDigits!=2, "+exchangeRateProvider.getToCurrency()+" has "+toFractionDigits+" defaultFractionDigits");
+
+        //ExchangeRate rate = exchangeRateProvider.getExchangeRate();
+        ExchangeRate rate;
+        if (reversibleExRate) {
+            rate = exchangeRateProvider.getReversibleExchangeRate(fromCurrency, toCurrency);
+        } else {
+            rate = exchangeRateProvider.getExchangeRate(fromCurrency, toCurrency);
         }
-        if (fromFranctionDigits!=2) {
-            throw new RuntimeException("Can't process currency with defaultFractionDigits!=2, "+exchangeRateProvider.getFromCurrency()+" has "+fromFranctionDigits+" defaultFractionDigits");
+        if (rate == null) {
+            return null;
         }
         
-        if (amount.signum()==-1) {
-            throw new RuntimeException("Can convert only non-negative value, current value is "+amount);
+        int fromFranctionDigits = fromCurrency.getDefaultFractionDigits();
+        int toFractionDigits = toCurrency.getDefaultFractionDigits();
+
+        if (toFractionDigits != 2) {
+            throw new ConvertorException("Can't process currency with defaultFractionDigits!=2, " + exchangeRateProvider.getToCurrency() + " has " + toFractionDigits + " defaultFractionDigits");
         }
-        
-        
+        if (fromFranctionDigits != 2) {
+            throw new ConvertorException("Can't process currency with defaultFractionDigits!=2, " + exchangeRateProvider.getFromCurrency() + " has " + fromFranctionDigits + " defaultFractionDigits");
+        }
+
+        if (amount.signum() == -1) {
+            throw new RuntimeException("Can convert only non-negative value, current value is " + amount);
+        }
+
+
         MathContext context = new MathContext(0, RoundingMode.DOWN);
-        
+
         BigDecimal from;
         BigDecimal to;
         if (convertBack) {
@@ -80,26 +125,89 @@
             to = rate.getFromValue();
             from = rate.getToValue();
         } else {
-            //converting in mornak way
+            //converting in normal way
             from = rate.getFromValue();
             to = rate.getToValue();
         }
 
         BigDecimal amountCent = amount.movePointRight(2);
-        
-        final BigDecimal multiplied = amountCent.multiply(to,context);
-        BigDecimal[] division = multiplied.divideAndRemainder(from,context);
+
+        final BigDecimal multiplied = amountCent.multiply(to, context);
+        BigDecimal[] division = multiplied.divideAndRemainder(from, context);
 
         if (!remainderAllowed && !(BigDecimal.ZERO.equals(division[1]))) {
-            throw new RuntimeException("Remained is not allowed - remaining amount is " + division[1]+ " cents");
+            throw new RuntimeException("Remained is not allowed - remaining amount is " + division[1] + " cents");
         } else {
             result.setRemainder(BigDecimal.ZERO);
         }
-        
-        final BigDecimal converted = division[0].movePointLeft(2);        
+
+        final BigDecimal converted = division[0].movePointLeft(2);
         result.setConverted(converted);
         //result.setRemainder(...);
-
         return result;
     }
+    
+
+    private ConversionResult convertValue(ConvertorCurrency fromCurrency, ConvertorCurrency toCurrency,BigDecimal amount, boolean convertBack,boolean reversibleExRate) throws RuntimeException {
+        //result.setRemainder(...);
+        if (convertors.length==0) {
+            return convertUsingSimpleConvertor(fromCurrency, toCurrency, reversibleExRate, amount, convertBack);
+        } else {
+            ConversionResult result = null;
+            for (int i = 0;i<convertors.length;i++) {
+                Convertor subConvertor = convertors[i];
+                result = subConvertor.convertValue(fromCurrency, toCurrency, amount, convertBack, reversibleExRate);
+                if (result!=null) {
+                    break;
+                }
+            }
+            return result;
+        }
+    }
+    
+    /**
+     * Convert <code>value</code> from <code>fromCurrency</code> to <code>toCurrency</code>.
+     * <p>
+     * Exchange rate is provided by exchange rate provider which was specified when Convertor was created.
+     * This method is using only exchange rate from->to and not trying to use reverted excange rate to->from.
+     * 
+     * @param fromCurrency Source currency to convert from.
+     * @param toCurrency Target currency to convert to.
+     * @param value Value in source currency which should be converted.
+     * @return Return conversion result.
+     * @since version2
+     * @throws ConversionNotSupportedException If conversion from <code>fromCurrency</code> to <code>toCurrency</code> is not supported.
+     */
+    public ConversionResult convert(ConvertorCurrency fromCurrency, ConvertorCurrency toCurrency, BigDecimal value) {
+        ConversionResult result = convertValue(fromCurrency, toCurrency, value, false,false);
+        if (result==null) {
+            //throw new ConversionNotSupportedException("Conversion from " + fromCurrency + " to " + toCurrency + " is not supported");
+            throw new ConversionNotSupportedException(fromCurrency.getCurrencyCode(),toCurrency.getCurrencyCode(),false);
+        }
+        return result;
+    }
+    
+    /**
+     * Convert <code>value</code> from <code>fromCurrency</code> to <code>toCurrency</code>.
+     * Exchange rate is provided by exchange rate provider which was specified when Convertor was created.
+     * <p>
+     *  This method is using only exchange rate from->to and if not found, it is trying to use reverted excange rate to->from.
+     * 
+     * @param fromCurrency Source currency to convert from.
+     * @param toCurrency Target currency to convert to.
+     * @param value Value in source currency which should be converted.
+     * @return Return conversion result.
+     * @since version2
+     * @throws ConversionNotSupportedException If conversion from <code>fromCurrency</code> to <code>toCurrency</code> 
+     *         is not supported and neither conversion from <code>toCurrency</code> to <code>fromCurrency</code> is not supported.
+     */
+    public ConversionResult convertWithReversibleRates(ConvertorCurrency fromCurrency, ConvertorCurrency toCurrency, BigDecimal value) {
+        ConversionResult result = convertValue(fromCurrency, toCurrency, value, false,true);
+        if (result==null) {
+            //throw new ConversionNotSupportedException("Neither onversion nor reverted conversion from " + fromCurrency + " to " + toCurrency + "  is not supported,");
+            throw new ConversionNotSupportedException(fromCurrency.getCurrencyCode(),toCurrency.getCurrencyCode(),true);
+        }
+        return result;
+    }
+    
 }