package org.apidesign.apifest08.currency;

 import java.math.BigDecimal;

 import java.math.MathContext;

 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 {

     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;       

     }

     /**

      * 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();

         c.exchangeRateProvider = exchangeRateProvider;

         return c;

     }

     /**

      * Convert <code>amount</code> from <code>fromCurrency</code> to <code>toCurrency</code> as specified

      * in <code>ExchangeRateProvider</code>.

      * 

      * @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(exchangeRateProvider.getFromCurrency(), exchangeRateProvider.getToCurrency(),amount, false,false);

     }

     /**

      * Convert <code>amount</code> from <code>toCurrency</code> to <code>fromCurrency</code> as specified

      * in <code>ExchangeRateProvider</code>. This is <em>reverted</em> order than suggested by  names of currency fields in <code>ExchangeRate</code>.

      * 

      * @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(exchangeRateProvider.getFromCurrency(), exchangeRateProvider.getToCurrency(),amount, true,false);

     }

     private ConversionResult convertUsingSimpleConvertor(ConvertorCurrency fromCurrency, ConvertorCurrency toCurrency, boolean reversibleExRate, BigDecimal amount, boolean convertBack) throws ConversionNotSupportedException, RuntimeException {

         ConversionResult result = new ConversionResult();

         //ExchangeRate rate = exchangeRateProvider.getExchangeRate();

         ExchangeRate rate;

         if (reversibleExRate) {

             rate = exchangeRateProvider.getReversibleExchangeRate(fromCurrency, toCurrency);

         } else {

             rate = exchangeRateProvider.getExchangeRate(fromCurrency, toCurrency);

         }

         if (rate == null) {

             return null;

         }

         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) {

             //converting in reverted way

             to = rate.getFromValue();

             from = rate.getToValue();

         } else {

             //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);

         if (!remainderAllowed && !(BigDecimal.ZERO.equals(division[1]))) {

             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);

         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;

     }

 }