package org.apidesign.apifest08.currency;

import java.util.Currency;

/** This is the skeleton class for your API. You need to make it public, so

 * it is accessible to your client code (currently in Task1Test.java) file.

 * <p>

 * Feel free to create additional classes or rename this one, just keep all

 * the API and its implementation in this package. Do not spread it outside

 * to other packages.

 */

public interface Convertor {

    /**

     * Converts by taking a request and producing a response.

     * If a convertor finds it cannot perform the requested conversion,

     * it should return a non-null {@link ConversionResult} that has null {@link ConversionResult#getNetAmount()}.

     * A convertor must not convert to a different currency than the one specified in the request.

     * <p>

     * When the need comes to extend the semantics, one subclasses the ConversionRequest and/or ConversionResult classes.

     * <p>

     * This method can be called as many times as you like.

     * A {@link Convertor} shall be considered immutable wrt calls to {@link #convert(org.apidesign.apifest08.currency.Convertor.ConversionRequest).

     * This method of a single {@link Convertor} can be called from many threads concurrently.

     * @param req the conversion request; mustn't be null

     * @return the result of carrying out the conversion request; never null

     * @throws IllegalRequestSubtypeException when the particular implementation cannot handle a specific ConversionRequest type

     */

    public ConversionResult convert( final ConversionRequest req ) throws IllegalRequestSubtypeException;

    /**

     * The request for converting a monetary amout into another currency.

     * Immutable.

     */

    public class ConversionRequest {

        private final MonetaryAmount srcAmount;

        private final Currency tgtCurrency;

        /**

         * A request to convert srcAmount into tgtCurrency.

         * @param srcAmount the source amount; must not be null

         * @param tgtCurrency the currency we want it in afterwards; must not be null

         */

        public ConversionRequest( final MonetaryAmount srcAmount, final Currency tgtCurrency ) {

            this.srcAmount = srcAmount;

            this.tgtCurrency = tgtCurrency;

            if ( srcAmount == null ) {

                throw new NullPointerException( "The source amount" );

            }

            if ( tgtCurrency == null ) {

                throw new NullPointerException( "The target currency" );

            }

            if ( srcAmount.getCurrency().equals( tgtCurrency ) ) {

                throw new IllegalArgumentException( "Cannot request conversion from " + srcAmount.getCurrency() + " to " + tgtCurrency );

            }

        }

        /**

         * The source amount.

         */

        public MonetaryAmount getSrcAmount() {

            return srcAmount;

        }

        /**

         * The target currency.

         */

        public Currency getTgtCurrency() {

            return tgtCurrency;

        }

    }

    /**

     * The result of converting a monetary amount into another currency.

     * For now it records just the net amount one recieves from the conversion.

     * Immutable.

     * <p>

     * <b>Extension note:</b> 

     * Other items can be added further down the road, as the need for them arises.

     * These items might provide info on other aspects of the conversion,

     * such as the fee or a reason why the conversion might not be admissible.

     */

    public class ConversionResult {

        private final MonetaryAmount netAmount;

        /**

         * A new conversion result.

         * @param netAmount the amount one recieves from the conversion; 

         * null means the conversion was not admissible

         */

        public ConversionResult( final MonetaryAmount netAmount ) {

            this.netAmount = netAmount;

        }

        /**

         * The amount one recieves from the conversion.

         * If null, the conversion is not admissible.

         * @return the amount

         */

        public MonetaryAmount getNetAmount() {

            return netAmount;

        }

    }

}