Refactor some on-spec logic into helper types

core/cron.go

@@ -80,17 +80,63 @@ var weekdays = map[string]time.Weekday{
 	"Sat": time.Saturday,
 }
 
+type ymd struct {
+	Year  int
+	Month time.Month
+	Day   int
+}
+
+type onSpecDate interface {
+	getDates(base time.Time) []ymd
+}
+
+type onSpecWeekday struct {
+	weekday time.Weekday
+}
+
+func (date *onSpecWeekday) getDates(base time.Time) (dates []ymd) {
+	// For a weekday, add the next of that weekday 0-6 days ahead and 7-13 days ahead.
+	// The first date ensures that we don't miss multiple updates on the same day of the week
+	// (e.g. "on Sun at 06:00,18:00") and the second date ensures that we don't get stuck with
+	// only a date in the past (e.g. "on Sun at 02:00" when base is Sun 03:00).
+	daysForward := (int(date.weekday) - int(base.Weekday()) + 7) % 7 // value in [0,6]
+	day0_6 := base.AddDate(0, 0, daysForward)
+	dates = append(dates, ymd{day0_6.Year(), day0_6.Month(), day0_6.Day()})
+	day7_13 := base.AddDate(0, 0, daysForward+7)
+	dates = append(dates, ymd{day7_13.Year(), day7_13.Month(), day7_13.Day()})
+	return
+}
+
+type onSpecEveryMonth struct {
+	day int
+}
+
+func (date *onSpecEveryMonth) getDates(base time.Time) (dates []ymd) {
+	// For every-month, add the date for the current month and the date for the next month.
+	dates = append(dates, ymd{base.Year(), base.Month(), date.day})
+	nextMonth := base.AddDate(0, 1, 0)
+	dates = append(dates, ymd{nextMonth.Year(), nextMonth.Month(), date.day})
+	return
+}
+
+type onSpecMonthDay struct {
+	month int
+	day   int
+}
+
+func (date *onSpecMonthDay) getDates(base time.Time) (dates []ymd) {
+	// For month/day, add the date for the base year and the next year.
+	dates = append(dates, ymd{base.Year(), time.Month(date.month), date.day})
+	dates = append(dates, ymd{base.Year() + 1, time.Month(date.month), date.day})
+	return
+}
+
 // Get the next instances of the on-spec times after the base time.
 // An on-spec is in the pattern DOW[,DOW[...]] where DOW is an abbreviated weekday
 // or M/D[,M/D[...]] where M/D is a month and day.
 // As a special case, "*/N" matches the Nth day of every month.
 // An on-spec may be followed by an at-spec; otherwise, "at 00:00" is implied.
 func parseOnSpec(base time.Time, onSpec string) (nextUpdates []time.Time, err error) {
-	type Date struct {
-		Year  int
-		Month time.Month
-		Day   int
-	}
 	type Time struct {
 		Hour   int
 		Minute int
@@ -111,38 +157,27 @@ func parseOnSpec(base time.Time, onSpec string) (nextUpdates []time.Time, err er
 		atTimes = append(atTimes, Time{hour, minute})
 	}
 
-	var dates []Date
+	var dates []ymd
 	for _, daySpec := range strings.Split(onSpec, ",") {
+		var date onSpecDate
 		if weekday, ok := weekdays[daySpec]; ok {
-			// For a weekday, add the next of that weekday 0-6 days ahead and 7-13 days ahead.
-			// The first date ensures that we don't miss multiple updates on the same day of the week
-			// (e.g. "on Sun at 06:00,18:00") and the second date ensures that we don't get stuck with
-			// only a date in the past (e.g. "on Sun at 02:00" when base is Sun 03:00).
-			daysForward := (int(weekday) - int(base.Weekday()) + 7) % 7 // value in [0,6]
-			day0_6 := base.AddDate(0, 0, daysForward)
-			dates = append(dates, Date{day0_6.Year(), day0_6.Month(), day0_6.Day()})
-			day7_13 := base.AddDate(0, 0, daysForward+7)
-			dates = append(dates, Date{day7_13.Year(), day7_13.Month(), day7_13.Day()})
+			date = &onSpecWeekday{weekday}
 		} else if strings.HasPrefix(daySpec, "*/") {
-			// For every-month, add the date for the current month and the date for the next month.
 			var day int
 			_, err := fmt.Sscanf(daySpec, "*/%d", &day)
 			if err != nil {
 				return nil, fmt.Errorf("could not parse month/day %s: %v", daySpec, err)
 			}
-			dates = append(dates, Date{base.Year(), base.Month(), day})
-			nextMonth := base.AddDate(0, 1, 0)
-			dates = append(dates, Date{nextMonth.Year(), nextMonth.Month(), day})
+			date = &onSpecEveryMonth{day}
 		} else {
-			// For month/day, add the date for the base year and the next year.
 			var month, day int
 			_, err := fmt.Sscanf(daySpec, "%d/%d", &month, &day)
 			if err != nil {
 				return nil, fmt.Errorf("could not parse month/day %s: %v", daySpec, err)
 			}
-			dates = append(dates, Date{base.Year(), time.Month(month), day})
-			dates = append(dates, Date{base.Year() + 1, time.Month(month), day})
+			date = &onSpecMonthDay{month, day}
 		}
+		dates = append(dates, date.getDates(base)...)
 	}
 
 	// Now, for each date, create a datetime based on the at-spec.