code: public static int weekDayMapping(final WeekDay source, final WeekDay target, final int weekday) {
          return source.mapTo(weekday, target);
      }
docs: Performs weekday mapping between two weekday definitions.
  
  @param source  - source
  @param target  - target weekday definition
  @param weekday - value in source range.
  @return int - mapped value