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. This method is not try 

 * use reverted excahnage rate. 

 * <li>{@link #convertWithReversibleRates(ConvertorCurrency, ConvertorCurrency, BigDecimal)} - 

 * convert using exchange rate specified in exchange rate provide. This method

 * is not trying to use reverted exchange rate.

 * </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(toFractionDigits);

        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);

        }

        BigDecimal converted = division[0].movePointLeft(toFractionDigits);

        converted = converted.setScale(toFractionDigits); //XXX ugly

        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;

    }

}