package gw.currency

uses gw.pl.currency.MonetaryAmount

uses java.lang.IllegalArgumentException
uses java.lang.Iterable

@ReadOnly
enhancement GWIterableOfMonetaryAmountCoreEnhancement: Iterable<MonetaryAmount> {

  /**
   * Return the average of the MonetaryAmount elements,
   *   which must all be of the specified currency.
   */
  function average(currency : Currency) : MonetaryAmount {
    return this.average(currency, \ amt -> amt)
  }


  /**
   * Sums up the MonetaryAmount elements,
   *   which must all be of the specified currency.
   */
  function sum(currency : Currency) : MonetaryAmount {
    return this.sum(currency, \ amt -> amt)
  }

  /**
   * Sums up the MonetaryAmount elements, which must all be of the same currency.
   * In addition the Iterable must have at least one non-null element to dynamically
   * determine the needed currency.
   *
   * MAKE SURE TO CALL THIS METHOD ONLY IF YOU KNOW THAT YOU HAVE AT LEAST ONE
   * NON-NULL MONETARYAMOUNT IN THE ITERABLE.
   */
  function sumWithAtLeastOneNonNullCurrency() : MonetaryAmount {
    var currency = this.firstWhere(\ ma -> ma != null).Currency
    if (currency == null) {
      throw new IllegalArgumentException("This Iterable needs to have at least one non-null MonetaryAmount")
    }
    return this.sum(currency, \ amt -> amt)
  }
}