SET TERM ^ ;

CREATE OR ALTER FUNCTION GET_LAST_DAY_OF (PERIOD STRING16, D DATE)
RETURNS DATE
AS
BEGIN
  IF (D IS NULL) THEN
    D = CURRENT_DATE;

  IF ((UPPER(PERIOD) = 'WEEK') OR (UPPER(PERIOD) = 'W'))  THEN
    RETURN  DATEADD(DAY, 6 - MOD(EXTRACT(WEEKDAY FROM D) + 6, 7), D);

  IF ((UPPER(PERIOD) = 'MONTH') OR (UPPER(PERIOD) = 'M'))  THEN
    RETURN DATEADD(1 MONTH TO D) - EXTRACT(DAY FROM DATEADD(1 MONTH TO D));
END
^

SET TERM ; ^