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;

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(rateValue, 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 BigDecimal rateValue; // a rate between the first currency and the second currency

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

		private ConvertorDelegate(BigDecimal rateValue, Currency currencyFirst, Currency currencySecond) {

			this.rateValue = rateValue;

			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) {

				retVal = rateValue;

			} else {	

				//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));

		}

	}

}