1 files changed, 231 insertions, 0 deletions
diff --git a/modules/cron/parser.go b/modules/cron/parser.go
new file mode 100644
index 0000000000..4224fa9308
--- /dev/null
+++ b/modules/cron/parser.go
@@ -0,0 +1,231 @@
+package cron
+
+import (
+	"fmt"
+	"log"
+	"math"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Parse returns a new crontab schedule representing the given spec.
+// It returns a descriptive error if the spec is not valid.
+//
+// It accepts
+//   - Full crontab specs, e.g. "* * * * * ?"
+//   - Descriptors, e.g. "@midnight", "@every 1h30m"
+func Parse(spec string) (_ Schedule, err error) {
+	// Convert panics into errors
+	defer func() {
+		if recovered := recover(); recovered != nil {
+			err = fmt.Errorf("%v", recovered)
+		}
+	}()
+
+	if spec[0] == '@' {
+		return parseDescriptor(spec), nil
+	}
+
+	// Split on whitespace.  We require 5 or 6 fields.
+	// (second) (minute) (hour) (day of month) (month) (day of week, optional)
+	fields := strings.Fields(spec)
+	if len(fields) != 5 && len(fields) != 6 {
+		log.Panicf("Expected 5 or 6 fields, found %d: %s", len(fields), spec)
+	}
+
+	// If a sixth field is not provided (DayOfWeek), then it is equivalent to star.
+	if len(fields) == 5 {
+		fields = append(fields, "*")
+	}
+
+	schedule := &SpecSchedule{
+		Second: getField(fields[0], seconds),
+		Minute: getField(fields[1], minutes),
+		Hour:   getField(fields[2], hours),
+		Dom:    getField(fields[3], dom),
+		Month:  getField(fields[4], months),
+		Dow:    getField(fields[5], dow),
+	}
+
+	return schedule, nil
+}
+
+// getField returns an Int with the bits set representing all of the times that
+// the field represents.  A "field" is a comma-separated list of "ranges".
+func getField(field string, r bounds) uint64 {
+	// list = range {"," range}
+	var bits uint64
+	ranges := strings.FieldsFunc(field, func(r rune) bool { return r == ',' })
+	for _, expr := range ranges {
+		bits |= getRange(expr, r)
+	}
+	return bits
+}
+
+// getRange returns the bits indicated by the given expression:
+//   number | number "-" number [ "/" number ]
+func getRange(expr string, r bounds) uint64 {
+
+	var (
+		start, end, step uint
+		rangeAndStep     = strings.Split(expr, "/")
+		lowAndHigh       = strings.Split(rangeAndStep[0], "-")
+		singleDigit      = len(lowAndHigh) == 1
+	)
+
+	var extra_star uint64
+	if lowAndHigh[0] == "*" || lowAndHigh[0] == "?" {
+		start = r.min
+		end = r.max
+		extra_star = starBit
+	} else {
+		start = parseIntOrName(lowAndHigh[0], r.names)
+		switch len(lowAndHigh) {
+		case 1:
+			end = start
+		case 2:
+			end = parseIntOrName(lowAndHigh[1], r.names)
+		default:
+			log.Panicf("Too many hyphens: %s", expr)
+		}
+	}
+
+	switch len(rangeAndStep) {
+	case 1:
+		step = 1
+	case 2:
+		step = mustParseInt(rangeAndStep[1])
+
+		// Special handling: "N/step" means "N-max/step".
+		if singleDigit {
+			end = r.max
+		}
+	default:
+		log.Panicf("Too many slashes: %s", expr)
+	}
+
+	if start < r.min {
+		log.Panicf("Beginning of range (%d) below minimum (%d): %s", start, r.min, expr)
+	}
+	if end > r.max {
+		log.Panicf("End of range (%d) above maximum (%d): %s", end, r.max, expr)
+	}
+	if start > end {
+		log.Panicf("Beginning of range (%d) beyond end of range (%d): %s", start, end, expr)
+	}
+
+	return getBits(start, end, step) | extra_star
+}
+
+// parseIntOrName returns the (possibly-named) integer contained in expr.
+func parseIntOrName(expr string, names map[string]uint) uint {
+	if names != nil {
+		if namedInt, ok := names[strings.ToLower(expr)]; ok {
+			return namedInt
+		}
+	}
+	return mustParseInt(expr)
+}
+
+// mustParseInt parses the given expression as an int or panics.
+func mustParseInt(expr string) uint {
+	num, err := strconv.Atoi(expr)
+	if err != nil {
+		log.Panicf("Failed to parse int from %s: %s", expr, err)
+	}
+	if num < 0 {
+		log.Panicf("Negative number (%d) not allowed: %s", num, expr)
+	}
+
+	return uint(num)
+}
+
+// getBits sets all bits in the range [min, max], modulo the given step size.
+func getBits(min, max, step uint) uint64 {
+	var bits uint64
+
+	// If step is 1, use shifts.
+	if step == 1 {
+		return ^(math.MaxUint64 << (max + 1)) & (math.MaxUint64 << min)
+	}
+
+	// Else, use a simple loop.
+	for i := min; i <= max; i += step {
+		bits |= 1 << i
+	}
+	return bits
+}
+
+// all returns all bits within the given bounds.  (plus the star bit)
+func all(r bounds) uint64 {
+	return getBits(r.min, r.max, 1) | starBit
+}
+
+// parseDescriptor returns a pre-defined schedule for the expression, or panics
+// if none matches.
+func parseDescriptor(spec string) Schedule {
+	switch spec {
+	case "@yearly", "@annually":
+		return &SpecSchedule{
+			Second: 1 << seconds.min,
+			Minute: 1 << minutes.min,
+			Hour:   1 << hours.min,
+			Dom:    1 << dom.min,
+			Month:  1 << months.min,
+			Dow:    all(dow),
+		}
+
+	case "@monthly":
+		return &SpecSchedule{
+			Second: 1 << seconds.min,
+			Minute: 1 << minutes.min,
+			Hour:   1 << hours.min,
+			Dom:    1 << dom.min,
+			Month:  all(months),
+			Dow:    all(dow),
+		}
+
+	case "@weekly":
+		return &SpecSchedule{
+			Second: 1 << seconds.min,
+			Minute: 1 << minutes.min,
+			Hour:   1 << hours.min,
+			Dom:    all(dom),
+			Month:  all(months),
+			Dow:    1 << dow.min,
+		}
+
+	case "@daily", "@midnight":
+		return &SpecSchedule{
+			Second: 1 << seconds.min,
+			Minute: 1 << minutes.min,
+			Hour:   1 << hours.min,
+			Dom:    all(dom),
+			Month:  all(months),
+			Dow:    all(dow),
+		}
+
+	case "@hourly":
+		return &SpecSchedule{
+			Second: 1 << seconds.min,
+			Minute: 1 << minutes.min,
+			Hour:   all(hours),
+			Dom:    all(dom),
+			Month:  all(months),
+			Dow:    all(dow),
+		}
+	}
+
+	const every = "@every "
+	if strings.HasPrefix(spec, every) {
+		duration, err := time.ParseDuration(spec[len(every):])
+		if err != nil {
+			log.Panicf("Failed to parse duration %s: %s", spec, err)
+		}
+		return Every(duration)
+	}
+
+	log.Panicf("Unrecognized descriptor: %s", spec)
+	return nil
+}