Initial Backupper Unraid plugin

internal/scheduler/cron.go

@@ -0,0 +1,96 @@
+package scheduler
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"time"
+)
+
+type Expression struct{ fields [5]field }
+type field map[int]bool
+
+var bounds = [5][2]int{{0, 59}, {0, 23}, {1, 31}, {1, 12}, {0, 6}}
+
+func Parse(spec string) (Expression, error) {
+	parts := strings.Fields(spec)
+	if len(parts) != 5 {
+		return Expression{}, fmt.Errorf("cron requires five fields")
+	}
+	var expression Expression
+	for i, part := range parts {
+		parsed, err := parseField(part, bounds[i][0], bounds[i][1])
+		if err != nil {
+			return Expression{}, fmt.Errorf("cron field %d: %w", i+1, err)
+		}
+		expression.fields[i] = parsed
+	}
+	return expression, nil
+}
+
+func parseField(value string, min, max int) (field, error) {
+	result := field{}
+	for _, segment := range strings.Split(value, ",") {
+		step := 1
+		base := segment
+		if strings.Contains(segment, "/") {
+			parts := strings.Split(segment, "/")
+			if len(parts) != 2 {
+				return nil, fmt.Errorf("invalid step %q", segment)
+			}
+			base = parts[0]
+			var err error
+			step, err = strconv.Atoi(parts[1])
+			if err != nil || step < 1 {
+				return nil, fmt.Errorf("invalid step %q", parts[1])
+			}
+		}
+		start, end := min, max
+		if base != "*" {
+			if strings.Contains(base, "-") {
+				parts := strings.Split(base, "-")
+				if len(parts) != 2 {
+					return nil, fmt.Errorf("invalid range %q", base)
+				}
+				start, _ = strconv.Atoi(parts[0])
+				end, _ = strconv.Atoi(parts[1])
+			} else {
+				var err error
+				start, err = strconv.Atoi(base)
+				end = start
+				if err != nil {
+					return nil, fmt.Errorf("invalid value %q", base)
+				}
+			}
+		}
+		if start < min || end > max || start > end {
+			return nil, fmt.Errorf("value outside %d-%d", min, max)
+		}
+		for n := start; n <= end; n += step {
+			result[n] = true
+		}
+	}
+	return result, nil
+}
+
+func (e Expression) Matches(t time.Time) bool {
+	values := [5]int{t.Minute(), t.Hour(), t.Day(), int(t.Month()), int(t.Weekday())}
+	for i, value := range values {
+		if !e.fields[i][value] {
+			return false
+		}
+	}
+	return true
+}
+
+func (e Expression) Next(after time.Time) time.Time {
+	t := after.Truncate(time.Minute).Add(time.Minute)
+	limit := t.AddDate(2, 0, 0)
+	for t.Before(limit) {
+		if e.Matches(t) {
+			return t
+		}
+		t = t.Add(time.Minute)
+	}
+	return time.Time{}
+}