fix(cron): next time calculation for expressions with L or W modifiers (#168)

Author: reugn

internal/csm/day_node.go

@@ -94,15 +94,50 @@ func (n *DayNode) findForward() result {
 }
 
 func (n *DayNode) isValid() bool {
-	withinLimits := n.isValidDay()
+	if !n.isValidDay() {
+		return false
+	}
+
 	if n.isWeekday() {
-		withinLimits = withinLimits && n.isValidWeekday()
+		return n.isValidWeekday()
 	}
-	return withinLimits
+
+	return n.isValidDayOfMonth()
 }
 
 func (n *DayNode) isValidWeekday() bool {
-	return contains(n.weekdayValues, n.getWeekday())
+	if n.n == 0 {
+		return contains(n.weekdayValues, n.getWeekday())
+	}
+
+	daysOfWeek := n.daysOfWeekInMonth()
+	if n.n > len(daysOfWeek) {
+		return false
+	}
+
+	if n.n > 0 {
+		return n.Value() == daysOfWeek[n.n-1]
+	}
+
+	return n.Value() == daysOfWeek[len(daysOfWeek)-1]
+}
+
+func (n *DayNode) isValidDayOfMonth() bool {
+	switch {
+	case n.n == 0:
+	case n.n < 0:
+		return n.Value() == n.max()+n.n
+	case n.n == NLastDayOfMonth:
+		return n.Value() == n.max()
+	case n.n&NWeekday != 0:
+		dayDate := n.dayDate()
+		if n.n&NLastDayOfMonth != 0 {
+			return n.Value() == n.max() && isWeekday(dayDate)
+		}
+		return isWeekday(dayDate)
+	}
+
+	return true
 }
 
 func (n *DayNode) isValidDay() bool {
@@ -114,18 +149,20 @@ func (n *DayNode) isWeekday() bool {
 }
 
 func (n *DayNode) getWeekday() int {
-	date := makeDateTime(n.year.Value(), n.month.Value(), n.c.value)
-	return int(date.Weekday())
+	return int(n.dayDate().Weekday())
 }
 
 func (n *DayNode) addDays(offset int) (overflowed bool) {
 	overflowed = n.Value()+offset > n.max()
-	today := makeDateTime(n.year.Value(), n.month.Value(), n.c.value)
-	newDate := today.AddDate(0, 0, offset)
+	newDate := n.dayDate().AddDate(0, 0, offset)
 	n.c.value = newDate.Day()
 	return
 }
 
+func (n *DayNode) dayDate() time.Time {
+	return makeDateTime(n.year.Value(), n.month.Value(), n.c.value)
+}
+
 func (n *DayNode) max() int {
 	month := time.Month(n.month.Value())
 	year := n.year.Value()

quartz/cron_test.go

@@ -285,10 +285,18 @@ func TestCronExpressionDayOfMonth(t *testing.T) {
 			expression: "0 15 10 L * ?",
 			expected:   "Mon Mar 31 10:15:00 2025",
 		},
+		{
+			expression: "0 15 12 L * ?",
+			expected:   "Mon Mar 31 12:15:00 2025",
+		},
 		{
 			expression: "0 15 10 L-5 * ?",
 			expected:   "Wed Mar 26 10:15:00 2025",
 		},
+		{
+			expression: "0 15 12 L-25 * ?",
+			expected:   "Thu Mar 6 12:15:00 2025",
+		},
 		{
 			expression: "0 15 10 15W * ?",
 			expected:   "Fri Mar 14 10:15:00 2025",
@@ -305,6 +313,11 @@ func TestCronExpressionDayOfMonth(t *testing.T) {
 			expression: "0 15 10 LW * ?",
 			expected:   "Mon Mar 31 10:15:00 2025",
 		},
+		// Verify no trigger in January, and in months with fewer than 31 days.
+		{
+			expression: "0 0 12 L-30 * ?",
+			expected:   "Sun Mar 1 12:00:00 2026",
+		},
 	}
 
 	prev := time.Date(2024, 1, 1, 12, 00, 00, 00, time.UTC).UnixNano()
@@ -330,6 +343,10 @@ func TestCronExpressionDayOfWeek(t *testing.T) {
 			expression: "0 15 10 ? * L",
 			expected:   "Sat Oct 26 10:15:00 2024",
 		},
+		{
+			expression: "0 15 12 ? * L",
+			expected:   "Sat Oct 26 12:15:00 2024",
+		},
 		{
 			expression: "0 15 10 ? * 5L",
 			expected:   "Thu Oct 31 10:15:00 2024",
@@ -342,6 +359,10 @@ func TestCronExpressionDayOfWeek(t *testing.T) {
 			expression: "0 15 10 ? * 2#1",
 			expected:   "Mon Nov 4 10:15:00 2024",
 		},
+		{
+			expression: "0 15 12 ? * 2#1",
+			expected:   "Mon Oct 7 12:15:00 2024",
+		},
 		{
 			expression: "0 15 10 ? * MON#1",
 			expected:   "Mon Nov 4 10:15:00 2024",