feat: add cron segment checker

checker.go

@@ -0,0 +1,92 @@
+package gronx
+
+import (
+	"strconv"
+	"strings"
+	"time"
+)
+
+type Checker interface {
+	GetRef() time.Time
+	SetRef(ref time.Time)
+	CheckDue(segment string, pos int) (bool, error)
+}
+
+type SegmentChecker struct {
+	ref time.Time
+}
+
+func (c *SegmentChecker) GetRef() time.Time {
+	return c.ref
+}
+
+func (c *SegmentChecker) SetRef(ref time.Time) {
+	c.ref = ref
+}
+
+func (c *SegmentChecker) CheckDue(segment string, pos int) (bool, error) {
+	ref := c.GetRef()
+	val, loc := valueByPos(ref, pos), ref.Location()
+
+	for _, offset := range strings.Split(segment, ",") {
+		mod := pos == 2 || pos == 4
+		due, err := c.isOffsetDue(offset, val)
+
+		if due || (!mod && err != nil) {
+			return due, err
+		}
+		if mod && !strings.ContainsAny(offset, "LW#") {
+			continue
+		}
+
+		last := time.Date(ref.Year(), ref.Month(), 1, 0, 0, 0, 0, loc).AddDate(0, 1, 0).Add(-time.Nanosecond).Day()
+		if pos == 2 {
+			return isValidMonthDay(offset, last, ref)
+		}
+		if pos == 4 {
+			return isValidWeekDay(offset, last, ref)
+		}
+	}
+
+	return false, nil
+}
+
+func (c *SegmentChecker) isOffsetDue(offset string, val int) (bool, error) {
+	if strings.Contains(offset, "/") && inStep(val, offset) {
+		return true, nil
+	}
+
+	if strings.Contains(offset, "-") && inRange(val, offset) {
+		return true, nil
+	}
+
+	if val == 0 || offset == "0" {
+		return offset == "0" && val == 0, nil
+	}
+
+	nval, err := strconv.Atoi(offset)
+	if err != nil {
+		return false, err
+	}
+
+	return nval == val, nil
+}
+
+func valueByPos(ref time.Time, pos int) int {
+	switch pos {
+	case 0:
+		return ref.Minute()
+	case 1:
+		return ref.Hour()
+	case 2:
+		return ref.Day()
+	case 3:
+		return int(ref.Month())
+	case 4:
+		return int(ref.Weekday())
+	case 5:
+		return ref.Year()
+	}
+
+	return 0
+}