package org.apidesign.apifest08.currency;

import java.util.Currency;

import java.util.HashMap;

import java.util.Map;

/**

 * A {@link Convertor} that works from a pre-set conversion table.

 * First use {@link #putIntoTable(org.apidesign.apifest08.currency.ConversionRate)} to set the conversion table.

 * Then invoke the {@link #convert(org.apidesign.apifest08.currency.Convertor.ConversionRequest)} method as many times as you wish.

 * @author jdvorak

 */

public class TableConvertor implements Convertor {

    private final Map<Currency, Map<Currency, ConversionRate>> conversionTable = new HashMap<Currency, Map<Currency, ConversionRate>>();

    public TableConvertor() {

    }

    /**

     * Puts a rate into the table.

     * @param rate

     */

    public void putIntoTable( final ConversionRate rate ) {

        final Currency srcCurrency = rate.getSrcUnitAmount().getCurrency();

        final Currency tgtCurrency = rate.getTgtUnitAmount().getCurrency();

        synchronized ( conversionTable ) {

            Map<Currency, ConversionRate> targetTable = conversionTable.get( srcCurrency );

            if ( targetTable == null ) {

                targetTable = new HashMap<Currency, ConversionRate>();

                conversionTable.put( srcCurrency, targetTable );

            }

            targetTable.put( tgtCurrency, rate );

        }

    }

    /**

     * Carries out the conversion.

     * If the table does not contain a conversion from the source currency to the target one,

     * a {@link ConversionResult} is returned that has null netAmount.

     * This implementation works with any {@link ConversionRequest}, it won't throw {@link IllegalRequestSubtypeException}.

     * @param req the conversion request

     * @return the conversion result

     */

    public ConversionResult convert( final ConversionRequest req ) {

        final Currency srcCurrency = req.getSrcAmount().getCurrency();

        final Currency tgtCurrency = req.getTgtCurrency();

        final ConversionRate rate = findConversionRate( srcCurrency, tgtCurrency );

        if ( rate != null ) {

            final MonetaryAmount tgtAmount = rate.convert( req.getSrcAmount() );

            return new ConversionResult( tgtAmount );

        } else {

            return new ConversionResult( null );    // did not find the pair of currencies in the table

        }

    }

    /**

     * Looks up the conversion between the given currencies in the table.

     * @param srcCurrency the source currency

     * @param tgtCurrency the target currency

     * @return the conversion rate; null means no conversion between the currencies was found in the table

     */

    protected ConversionRate findConversionRate( final Currency srcCurrency, final Currency tgtCurrency ) {

        synchronized ( conversionTable ) {

            final Map<Currency, ConversionRate> targetTable = conversionTable.get(srcCurrency);

            final ConversionRate rate = (targetTable != null) ? targetTable.get(tgtCurrency) : null;

            return rate;

        }

    }

}