package org.apidesign.apifest08.currency;

import java.lang.ref.WeakReference;

import java.math.BigDecimal;

import java.util.Currency;

import java.util.Map;

import java.util.WeakHashMap;

/**

 * Create convertors using a flyweight to reduce the number of repetative creations of the same convertor.

 * 

 * @author D'Arcy Smith

 * @version 1.0

 */

public final class ConvertorFactory

{

    /**

     * flyweight so that only one vestion of each converter is created at a time.

     */

    private final static Map<String, WeakReference<Convertor>> convertors;

    static

    {

        convertors = new WeakHashMap<String, WeakReference<Convertor>>();

    }

    /** 

     * Prevent accidental construction.

     */

    private ConvertorFactory()

    {        

    }

    /**

     * Get the convertor for the specified currencies.  The currency name format

     * must be acceptable to java.util.Currency.getInstance(String)

     * 

     * @param a the currency to convert from.

     * @param aRate the exchange rate for a to b.

     * @param b the currency to convert to.

     * @param bRate the echante rate for b to a.

     * @return the convertor for the specified currencies.

     * @throws IllegalArgumentException if any of the arguments are null.

     */

    public static Convertor getConvertor(final String     a,

                                         final BigDecimal aRate,

                                         final String     b,

                                         final BigDecimal bRate)

    {

        final Currency  currencyA;

        final Currency  currencyB;

        final Convertor convertor;

        currencyA = Currency.getInstance(a);

        currencyB = Currency.getInstance(b);        

        convertor = getConvertor(currencyA, aRate, currencyB, bRate);

        return (convertor);

    }

    /**

     * Get the convertor for the specified currencies.

     * 

     * @param a the currency to convert from.

     * @param aRate the exchange rate for a to b.

     * @param b the currency to convert to.

     * @param bRate the echante rate for b to a.

     * @return the convertor for the specified currencies.

     * @throws IllegalArgumentException if either any of the arguments are null or if either rate <= 0.

     */

    public static Convertor getConvertor(final Currency   a,

                                         final BigDecimal aRate,

                                         final Currency   b,

                                         final BigDecimal bRate)

    {

        final String key;        

        Convertor    convertor;

        if(a == null)

        {

            throw new IllegalArgumentException("a cannot be null");

        }

        if(b == null)

        {

            throw new IllegalArgumentException("b cannot be null");

        }

        if(aRate == null)

        {

            throw new IllegalArgumentException("aRate cannot be null");

        }

        if(bRate == null)

        {

            throw new IllegalArgumentException("bRate cannot be null");

        }

        key = a.getCurrencyCode() + aRate + b.getCurrencyCode() + bRate;

        // make sure that we don't try to overwrite one

        synchronized(convertors)

        {

            if(!(convertors.containsKey(key)))

            {        

                convertor = new ConvertorImpl(a, aRate, b, bRate);

                convertors.put(key, new WeakReference(convertor));

            }

        }

        convertor = convertors.get(key).get();

        return (convertor);

    }

}