datetime - Groovy - idiomatic way of coding The Last Weekday - First of Month -

what groovy idiomatic way of asking last past weekday (ex. monday)? (or current week, first day of week)?

also there similar asking current month, first of month?

static date firstdayinweek(date day) {     day.cleartime()     return day - day.calendardate.dayofweek }