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" );

        }

    }

}