feat(cron): add support for day-of-month special characters

README.md

@@ -108,7 +108,7 @@ Several common Job implementations can be found in the [job](./job) package.
 | Seconds      | YES       | 0-59            | , - * /                    |
 | Minutes      | YES       | 0-59            | , - * /                    |
 | Hours        | YES       | 0-23            | , - * /                    |
-| Day of month | YES       | 1-31            | , - * ? /                  |
+| Day of month | YES       | 1-31            | , - * ? / L W              |
 | Month        | YES       | 1-12 or JAN-DEC | , - * /                    |
 | Day of week  | YES       | 1-7 or SUN-SAT  | , - * ? / L #              |
 | Year         | NO        | empty, 1970-    | , - * /                    |

internal/csm/common_node.go

@@ -70,7 +70,7 @@ func (n *CommonNode) nextInRange() bool {
 func (n *CommonNode) isValid() bool {
 	withinLimits := n.value >= n.min && n.value <= n.max
 	if n.hasRange() {
-		withinLimits = withinLimits && contained(n.value, n.values)
+		withinLimits = withinLimits && contains(n.values, n.value)
 	}
 	return withinLimits
 }

internal/csm/day_node.go

@@ -2,6 +2,11 @@ package csm
 
 import "time"
 
+const (
+	NLastDayOfMonth = 1
+	NWeekday        = 2
+)
+
 type DayNode struct {
 	c             CommonNode
 	weekdayValues []int
@@ -12,10 +17,11 @@ type DayNode struct {
 
 var _ csmNode = (*DayNode)(nil)
 
-func NewMonthDayNode(value, min, max int, dayOfMonthValues []int, month, year csmNode) *DayNode {
+func NewMonthDayNode(value, min, max, n int, dayOfMonthValues []int, month, year csmNode) *DayNode {
 	return &DayNode{
 		c:             CommonNode{value, min, max, dayOfMonthValues},
 		weekdayValues: make([]int, 0),
+		n:             n,
 		month:         month,
 		year:          year,
 	}
@@ -47,7 +53,10 @@ func (n *DayNode) Next() (overflowed bool) {
 		}
 		return n.nextWeekdayN()
 	}
-	return n.nextDay()
+	if n.n == 0 {
+		return n.nextDay()
+	}
+	return n.nextDayN()
 }
 
 func (n *DayNode) nextWeekday() (overflowed bool) {
@@ -91,7 +100,7 @@ func (n *DayNode) isValid() bool {
 }
 
 func (n *DayNode) isValidWeekday() bool {
-	return contained(n.getWeekday(), n.weekdayValues)
+	return contains(n.weekdayValues, n.getWeekday())
 }
 
 func (n *DayNode) isValidDay() bool {
@@ -103,13 +112,13 @@ func (n *DayNode) isWeekday() bool {
 }
 
 func (n *DayNode) getWeekday() int {
-	date := time.Date(n.year.Value(), time.Month(n.month.Value()), n.c.value, 0, 0, 0, 0, time.UTC)
+	date := makeDateTime(n.year.Value(), n.month.Value(), n.c.value)
 	return int(date.Weekday())
 }
 
 func (n *DayNode) addDays(offset int) (overflowed bool) {
 	overflowed = n.Value()+offset > n.max()
-	today := time.Date(n.year.Value(), time.Month(n.month.Value()), n.c.value, 0, 0, 0, 0, time.UTC)
+	today := makeDateTime(n.year.Value(), n.month.Value(), n.c.value)
 	newDate := today.AddDate(0, 0, offset)
 	n.c.value = newDate.Day()
 	return
@@ -126,10 +135,63 @@ func (n *DayNode) max() int {
 		month++
 	}
 
-	date := time.Date(year, month, 0, 0, 0, 0, 0, time.UTC)
+	date := makeDateTime(year, int(month), 0)
 	return date.Day()
 }
 
+func (n *DayNode) nextDayN() (overflowed bool) {
+	switch n.n {
+	case NWeekday:
+		n.nextWeekdayOfMonth()
+	default:
+		n.nextLastDayOfMonth()
+	}
+	return
+}
+
+func (n *DayNode) nextWeekdayOfMonth() {
+	year := n.year.Value()
+	month := n.month.Value()
+
+	monthLastDate := lastDayOfMonth(year, month)
+	date := n.c.values[0]
+	if date > monthLastDate {
+		date = monthLastDate
+	}
+
+	monthDate := makeDateTime(year, month, date)
+	closest := closestWeekday(monthDate)
+	if n.c.value >= closest {
+		n.c.value = 0
+		n.advanceMonth()
+		n.nextWeekdayOfMonth()
+		return
+	}
+
+	n.c.value = closest
+}
+
+func (n *DayNode) nextLastDayOfMonth() {
+	year := n.year.Value()
+	month := n.month.Value()
+
+	firstDayOfMonth := makeDateTime(year, month, 1)
+	offset := n.n
+	if offset == NLastDayOfMonth {
+		offset = 0
+	}
+	dayOfMonth := firstDayOfMonth.AddDate(0, 1, offset-1)
+
+	if n.c.value >= dayOfMonth.Day() {
+		n.c.value = 0
+		n.advanceMonth()
+		n.nextLastDayOfMonth()
+		return
+	}
+
+	n.c.value = dayOfMonth.Day()
+}
+
 func (n *DayNode) nextWeekdayN() (overflowed bool) {
 	n.c.value = n.getDayInMonth(n.daysOfWeekInMonth())
 	return
@@ -170,10 +232,10 @@ func (n *DayNode) daysOfWeekInMonth() []int {
 	// the day of week specified for the node
 	weekday := n.weekdayValues[0]
 
-	var dates []int
+	dates := make([]int, 0, 5)
 	// iterate through all the days of the month
 	for day := 1; ; day++ {
-		currentDate := time.Date(year, time.Month(month), day, 0, 0, 0, 0, time.UTC)
+		currentDate := makeDateTime(year, month, day)
 		// stop if we have reached the next month
 		if currentDate.Month() != time.Month(month) {
 			break

internal/csm/util.go

@@ -1,11 +1,50 @@
 package csm
 
-// Returns true if the element is included in the slice.
-func contained[T comparable](element T, slice []T) bool {
+import (
+	"time"
+)
+
+// contains returns true if the element is included in the slice.
+func contains[T comparable](slice []T, element T) bool {
 	for _, e := range slice {
 		if element == e {
 			return true
 		}
 	}
 	return false
 }
+
+// closestWeekday returns the day of the closest weekday within the month of
+// the given time t.
+func closestWeekday(t time.Time) int {
+	if isWeekday(t) {
+		return t.Day()
+	}
+
+	for i := 1; i <= 7; i++ {
+		prevDay := t.AddDate(0, 0, -i)
+		if prevDay.Month() == t.Month() && isWeekday(prevDay) {
+			return prevDay.Day()
+		}
+
+		nextDay := t.AddDate(0, 0, i)
+		if nextDay.Month() == t.Month() && isWeekday(nextDay) {
+			return nextDay.Day()
+		}
+	}
+
+	return t.Day()
+}
+
+func isWeekday(t time.Time) bool {
+	return t.Weekday() != time.Saturday && t.Weekday() != time.Sunday
+}
+
+func lastDayOfMonth(year, month int) int {
+	firstDayOfMonth := makeDateTime(year, month, 1)
+	return firstDayOfMonth.AddDate(0, 1, -1).Day()
+}
+
+func makeDateTime(year, month, day int) time.Time {
+	return time.Date(year, time.Month(month), day, 0, 0, 0, 0, time.UTC)
+}

quartz/cron.go

@@ -29,6 +29,8 @@ import (
 //	"0 15 10 15 * ?"         Fire at 10:15am on the 15th day of every month
 //	"0 15 10 ? * 6L"         Fire at 10:15am on the last Friday of every month
 //	"0 15 10 ? * 6#3"        Fire at 10:15am on the third Friday of every month
+//	"0 15 10 L * ?"          Fire at 10:15am on the last day of every month
+//	"0 15 10 L-2 * ?"        Fire at 10:15am on the 2nd-to-last last day of every month
 type CronTrigger struct {
 	expression  string
 	fields      []*cronField
@@ -94,14 +96,8 @@ func (ct *CronTrigger) Description() string {
 type cronField struct {
 	// stores the parsed and sorted numeric values for the field
 	values []int
-	// n specifies the occurrence of the day of week within a
-	// month when '#' is used in the day-of-week field.
-	// When 'L' (last) is used, it will be set to -1.
-	//
-	// Examples:
-	//
-	//  - For "5#3" (third Thursday of the month), n will be 3.
-	//  - For "2L" (last Sunday of the month), n will be -1.
+	// n is used to store special values for the day-of-month
+	// and day-of-week fields
 	n int
 }
 
@@ -200,7 +196,7 @@ func buildCronField(tokens []string) ([]*cronField, error) {
 		return nil, err
 	}
 	// day-of-month field
-	fields[3], err = parseField(tokens[3], 1, 31)
+	fields[3], err = parseDayOfMonthField(tokens[3], 1, 31)
 	if err != nil {
 		return nil, err
 	}
@@ -269,12 +265,46 @@ func parseField(field string, min, max int, translate ...[]string) (*cronField,
 }
 
 var (
-	cronLastCharacterRegex = regexp.MustCompile(`^[0-9]*L$`)
-	cronHashCharacterRegex = regexp.MustCompile(`^[0-9]+#[0-9]+$`)
+	cronLastMonthDayRegex = regexp.MustCompile(`^L(-[0-9]+)?$`)
+	cronWeekdayRegex      = regexp.MustCompile(`^[0-9]+W$`)
+
+	cronLastWeekdayRegex = regexp.MustCompile(`^[0-9]*L$`)
+	cronHashRegex        = regexp.MustCompile(`^[0-9]+#[0-9]+$`)
 )
 
+func parseDayOfMonthField(field string, min, max int, translate ...[]string) (*cronField, error) {
+	if strings.ContainsRune(field, lastRune) && cronLastMonthDayRegex.MatchString(field) {
+		if field == string(lastRune) {
+			return newCronFieldN([]int{}, cronLastDayOfMonthN), nil
+		}
+		values := strings.Split(field, string(rangeRune))
+		if len(values) != 2 {
+			return nil, newInvalidCronFieldError("last", field)
+		}
+		n, err := strconv.Atoi(values[1])
+		if err != nil || !inScope(n, 1, 30) {
+			return nil, newInvalidCronFieldError("last", field)
+		}
+		return newCronFieldN([]int{}, -n), nil
+	}
+
+	if strings.ContainsRune(field, weekdayRune) && cronWeekdayRegex.MatchString(field) {
+		day := strings.TrimSuffix(field, string(weekdayRune))
+		if day == "" {
+			return nil, newInvalidCronFieldError("weekday", field)
+		}
+		dayOfMonth, err := strconv.Atoi(day)
+		if err != nil || !inScope(dayOfMonth, min, max) {
+			return nil, newInvalidCronFieldError("weekday", field)
+		}
+		return newCronFieldN([]int{dayOfMonth}, cronWeekdayN), nil
+	}
+
+	return parseField(field, min, max, translate...)
+}
+
 func parseDayOfWeekField(field string, min, max int, translate ...[]string) (*cronField, error) {
-	if strings.ContainsRune(field, lastRune) && cronLastCharacterRegex.MatchString(field) {
+	if strings.ContainsRune(field, lastRune) && cronLastWeekdayRegex.MatchString(field) {
 		day := strings.TrimSuffix(field, string(lastRune))
 		if day == "" { // Saturday
 			return newCronFieldN([]int{7}, -1), nil
@@ -286,7 +316,7 @@ func parseDayOfWeekField(field string, min, max int, translate ...[]string) (*cr
 		return newCronFieldN([]int{dayOfWeek}, -1), nil
 	}
 
-	if strings.ContainsRune(field, hashRune) && cronHashCharacterRegex.MatchString(field) {
+	if strings.ContainsRune(field, hashRune) && cronHashRegex.MatchString(field) {
 		values := strings.Split(field, string(hashRune))
 		if len(values) != 2 {
 			return nil, newInvalidCronFieldError("hash", field)

quartz/cron_test.go

@@ -238,6 +238,47 @@ func TestCronExpressionSpecial(t *testing.T) {
 	}
 }
 
+func TestCronExpressionDayOfMonth(t *testing.T) {
+	t.Parallel()
+	tests := []struct {
+		expression string
+		expected   string
+	}{
+		{
+			expression: "0 15 10 L * ?",
+			expected:   "Mon Mar 31 10:15:00 2025",
+		},
+		{
+			expression: "0 15 10 L-5 * ?",
+			expected:   "Wed Mar 26 10:15:00 2025",
+		},
+		{
+			expression: "0 15 10 15W * ?",
+			expected:   "Fri Mar 14 10:15:00 2025",
+		},
+		{
+			expression: "0 15 10 1W 1/2 ?",
+			expected:   "Wed Jul 1 10:15:00 2026",
+		},
+		{
+			expression: "0 15 10 31W * ?",
+			expected:   "Mon Mar 31 10:15:00 2025",
+		},
+	}
+
+	prev := time.Date(2024, 1, 1, 12, 00, 00, 00, time.UTC).UnixNano()
+	for _, tt := range tests {
+		test := tt
+		t.Run(test.expression, func(t *testing.T) {
+			t.Parallel()
+			cronTrigger, err := quartz.NewCronTrigger(test.expression)
+			assert.IsNil(t, err)
+			result, _ := iterate(prev, cronTrigger, 15)
+			assert.Equal(t, result, test.expected)
+		})
+	}
+}
+
 func TestCronExpressionDayOfWeek(t *testing.T) {
 	t.Parallel()
 	tests := []struct {
@@ -370,6 +411,14 @@ func TestCronExpressionParseError(t *testing.T) {
 		"0 0 0 * * 50#2",
 		"0 5,7 14 ? * 8L *",
 		"0 5,7 14 ? * -1L *",
+		"0 5,7 14 ? * 0L *",
+		"0 15 10 W * ?",
+		"0 15 10 0W * ?",
+		"0 15 10 32W * ?",
+		"0 15 10 W15 * ?",
+		"0 15 10 L- * ?",
+		"0 15 10 L-a * ?",
+		"0 15 10 L-32 * ?",
 	}
 
 	for _, tt := range tests {

quartz/csm.go

@@ -6,14 +6,19 @@ import (
 	CSM "github.com/reugn/go-quartz/internal/csm"
 )
 
+const (
+	cronLastDayOfMonthN = CSM.NLastDayOfMonth
+	cronWeekdayN        = CSM.NWeekday
+)
+
 func newCSMFromFields(prev time.Time, fields []*cronField) *CSM.CronStateMachine {
 	year := CSM.NewCommonNode(prev.Year(), 0, 999999, fields[6].values)
 	month := CSM.NewCommonNode(int(prev.Month()), 1, 12, fields[4].values)
 	var day *CSM.DayNode
 	if len(fields[5].values) != 0 {
 		day = CSM.NewWeekDayNode(prev.Day(), 1, 31, fields[5].n, fields[5].values, month, year)
 	} else {
-		day = CSM.NewMonthDayNode(prev.Day(), 1, 31, fields[3].values, month, year)
+		day = CSM.NewMonthDayNode(prev.Day(), 1, 31, fields[3].n, fields[3].values, month, year)
 	}
 	hour := CSM.NewCommonNode(prev.Hour(), 0, 59, fields[2].values)
 	minute := CSM.NewCommonNode(prev.Minute(), 0, 59, fields[1].values)