criar função personalizada para diferença de data excluindo fins de semana e feriados no oracle sql

CREATE FUNCTION getWorkingDays (
  in_start_date IN  DATE,
  in_end_date   IN  DATE
) RETURN NUMBER DETERMINISTIC
IS
  p_start_date   DATE;
  p_end_date     DATE;
  p_working_days NUMBER;
  p_holiday_days NUMBER;
BEGIN
  IF in_start_date IS NULL OR in_end_date IS NULL THEN
    RETURN NUll;
  END IF;

  p_start_date := LEAST( in_start_date, in_end_date );
  p_end_date   := GREATEST( in_start_date, in_end_date );

  -- 5/7 * ( Number of days between monday of the week containing the start date
  --         and monday of the week containing the end date )
  -- + LEAST( day of week for end date, 5 )
  -- - LEAST( day of week for start date, 5 )
  p_working_days := ( TRUNC( p_end_date, 'IW' ) - TRUNC( p_start_date, 'IW' ) ) * 5 / 7
                    + LEAST( p_end_date - TRUNC( p_end_date, 'IW' ), 5 )
                    - LEAST( p_start_date - TRUNC( p_start_date, 'IW' ), 5 );

  SELECT COALESCE(
           SUM(
             LEAST( p_end_date, holiday_date + INTERVAL '1' DAY )
             - GREATEST( p_start_date, holiday_date )
           ),
           0
         )
  INTO   p_holiday_days
  FROM   Holidays
  WHERE  HOLIDAY_DATE BETWEEN TRUNC( p_start_date )
                      AND     TRUNC( p_end_date )
  AND    HOLIDAY_DATE - TRUNC( HOLIDAY_DATE, 'IW' ) < 5;

  RETURN GREATEST( p_working_days - p_holiday_days, 0 );
END;
/