package org.apidesign.apifest08.currency;

 import java.math.BigDecimal;

 import java.math.RoundingMode;

 /**

  * A rate of conversion from one currency to another.

  * @author jdvorak

  */

 public class ConversionRate {

     private final MonetaryAmount srcUnitAmount;

     private final MonetaryAmount tgtUnitAmount;

     private final int tgtScale;

     private final RoundingMode roundingMode;

     /**

      * A new conversion rate that gives tgtUnitAmount per every srcUnitAmount.

      * @param srcUnitAmount the amount of source currency

      * @param tgtUnitAmount the corresponding amount of target currency

      * @param tgtScale the scale of the target amounts

      * @param roundingMode the rounding mode to use when producing the target amounts

      */

     public ConversionRate( final MonetaryAmount srcUnitAmount, final MonetaryAmount tgtUnitAmount, final int targetScale, final RoundingMode roundingMode ) {

         this.srcUnitAmount = srcUnitAmount;

         this.tgtUnitAmount = tgtUnitAmount;

         this.tgtScale = targetScale;

         this.roundingMode = roundingMode;

     }

     /**

      * A new conversion rate that gives tgtUnitAmount per every srcUnitAmount, default number of fraction digits and the given rounding mode.

      * @param srcUnitAmount the amount of source currency

      * @param tgtUnitAmount the corresponding amount of target currency

      * @param roundingMode the rounding mode to use

      */

     public ConversionRate( final MonetaryAmount srcUnitAmount, final MonetaryAmount tgtUnitAmount, final RoundingMode roundingMode ) {

         this( srcUnitAmount, tgtUnitAmount, tgtUnitAmount.getCurrency().getDefaultFractionDigits(), roundingMode );

     }

     /**

      * A new conversion rate that gives tgtUnitAmount per every srcUnitAmount, default number of fraction digits and {@link RoundingMode#HALF_EVEN}.

      * @param srcUnitAmount the amount of source currency

      * @param tgtUnitAmount the corresponding amount of target currency

      */

     public ConversionRate( final MonetaryAmount srcUnitAmount, final MonetaryAmount tgtUnitAmount ) {

         this( srcUnitAmount, tgtUnitAmount, RoundingMode.HALF_EVEN );

     }

     public RoundingMode getRoundingMode() {

         return roundingMode;

     }

     public MonetaryAmount getSrcUnitAmount() {

         return srcUnitAmount;

     }

     public int getTgtScale() {

         return tgtScale;

     }

     public MonetaryAmount getTgtUnitAmount() {

         return tgtUnitAmount;

     }

     /**

      * Multiplies the given amount with the given rate.

      * @param srcAmount

      * @return

      */

     public BigDecimal convert( final BigDecimal srcAmount ) {

         return srcAmount

             .multiply( tgtUnitAmount.getAmount() )

             .divide( srcUnitAmount.getAmount(), tgtScale, roundingMode );

     }

     /**

      * Creates a monetary amount that corresponds to the given source amount multiplied by the rate.

      * @param srcAmount the source amount

      * @return the monetary amount in the target currency

      * @throws IllegalArgumentException if the currency of srcAmount is not equal to the source currency of this rate

      */

     public MonetaryAmount convert( final MonetaryAmount srcAmount ) {

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

             return new MonetaryAmount( convert( srcAmount.getAmount() ), tgtUnitAmount.getCurrency() );

         } else {

             throw new IllegalArgumentException( "This rate converts from " + srcUnitAmount.getCurrency() + ", but a conversion from " + srcAmount.getCurrency() + " is attempted" );

         }

     }

 }