1 files changed, 280 insertions, 0 deletions
diff --git a/schedule/sched.go b/schedule/sched.go
new file mode 100644
index 0000000..417f3d8
--- /dev/null
+++ b/schedule/sched.go
@@ -0,0 +1,280 @@
+package schedule
+
+import (
+	"errors"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+	"time"
+)
+
+type TimeUnit int
+
+const timefmt = "2006-01-02 15:04:05"
+
+const (
+	Minute TimeUnit = iota
+	Hour
+	Day
+	Week
+	Month
+	Year
+)
+
+var nilTime time.Time
+
+var tuLookup = map[string]TimeUnit{
+	"Minute": Minute,
+	"Hour":   Hour,
+	"Day":    Day,
+	"Week":   Week,
+	"Month":  Month,
+	"Year":   Year,
+}
+
+func (tu TimeUnit) String() string {
+	switch tu {
+	case Minute:
+		return "Minute"
+	case Hour:
+		return "Hour"
+	case Day:
+		return "Day"
+	case Week:
+		return "Week"
+	case Month:
+		return "Month"
+	case Year:
+		return "Year"
+	default:
+		return "(Unknown TimeUnit)"
+	}
+}
+
+func (tu TimeUnit) minApprox() time.Duration {
+	const (
+		maMinute = time.Minute
+		maHour   = time.Hour
+		maDay    = 24*time.Hour - time.Second
+		maWeek   = 7 * maDay
+		maMonth  = 28 * maDay
+		maYear   = 365 * maDay
+	)
+
+	switch tu {
+	case Minute:
+		return maMinute
+	case Hour:
+		return maHour
+	case Day:
+		return maDay
+	case Week:
+		return maWeek
+	case Month:
+		return maMonth
+	case Year:
+		return maYear
+	default:
+		return 0
+	}
+}
+
+func (tu TimeUnit) maxApprox() time.Duration {
+	const (
+		maMinute = time.Minute
+		maHour   = time.Hour
+		maDay    = 24*time.Hour + time.Second
+		maWeek   = 7 * maDay
+		maMonth  = 31 * maDay
+		maYear   = 366 * maDay
+	)
+
+	switch tu {
+	case Minute:
+		return maMinute
+	case Hour:
+		return maHour
+	case Day:
+		return maDay
+	case Week:
+		return maWeek
+	case Month:
+		return maMonth
+	case Year:
+		return maYear
+	default:
+		return 0
+	}
+}
+
+type Frequency struct {
+	Unit  TimeUnit
+	Count uint
+}
+
+func (f Frequency) String() string {
+	return fmt.Sprintf("%d %s", f.Count, f.Unit)
+}
+
+func (f Frequency) addTo(t time.Time, mul uint) time.Time {
+	sec := t.Second()
+	min := t.Minute()
+	hour := t.Hour()
+	day := t.Day()
+	month := t.Month()
+	year := t.Year()
+	loc := t.Location()
+
+	fq := int(f.Count * mul)
+
+	switch f.Unit {
+	case Minute:
+		return t.Add(time.Minute * time.Duration(fq))
+	case Hour:
+		return t.Add(time.Hour * time.Duration(fq))
+	case Day:
+		return time.Date(year, month, day+fq, hour, min, sec, 0, loc)
+	case Week:
+		return time.Date(year, month, day+fq*7, hour, min, sec, 0, loc)
+	case Month:
+		return time.Date(year, month+time.Month(fq), day, hour, min, sec, 0, loc)
+	case Year:
+		return time.Date(year+fq, month, day, hour, min, sec, 0, loc)
+	default:
+		return nilTime
+	}
+}
+
+func (f Frequency) minApprox() time.Duration { return time.Duration(f.Count) * f.Unit.minApprox() }
+func (f Frequency) maxApprox() time.Duration { return time.Duration(f.Count) * f.Unit.maxApprox() }
+
+// Schedule describes a time schedule. It has a start and optional end point and an optional frequency.
+type Schedule struct {
+	Start, End time.Time
+	Freq       Frequency
+}
+
+// NextAfter calculates the next time in the schedule after t. If no such time exists, nil is returned (test with Time.IsZero()).
+func (c Schedule) NextAfter(t time.Time) time.Time {
+	if !t.After(c.Start) {
+		return c.Start
+	}
+	if c.Freq.Count == 0 {
+		return nilTime
+	}
+
+	d := t.Sub(c.Start)
+
+	fmin := uint(math.Floor(float64(d) / float64(c.Freq.maxApprox())))
+	fmax := uint(math.Ceil(float64(d) / float64(c.Freq.minApprox())))
+
+	for f := fmin; f <= fmax; f++ {
+		t2 := c.Freq.addTo(c.Start, f)
+		if t2.Before(c.Start) || t2.Before(t) {
+			continue
+		}
+		if (!c.End.IsZero()) && t2.After(c.End) {
+			return nilTime
+		}
+		return t2
+	}
+
+	return nilTime // Should actually never happen...
+}
+
+func (c Schedule) String() string {
+	s := c.Start.UTC().Format(timefmt)
+	if c.Freq.Count > 0 {
+		s += " +" + c.Freq.String()
+		if !c.End.IsZero() {
+			s += " !" + c.End.UTC().Format(timefmt)
+		}
+	}
+	return s
+}
+
+func ParseSchedule(s string) (c Schedule, err error) {
+	elems := strings.Split(s, " ")
+
+	switch len(elems) {
+	case 6: // Everything specified
+		_end := elems[4] + " " + elems[5]
+		if c.End, err = time.ParseInLocation(timefmt, _end[1:], time.UTC); err != nil {
+			return
+		}
+		fallthrough
+	case 4: // start time and frequency
+		var count uint64
+		if count, err = strconv.ParseUint(elems[2][1:], 10, 32); err != nil {
+			return
+		}
+		c.Freq.Count = uint(count)
+
+		var ok bool
+		if c.Freq.Unit, ok = tuLookup[elems[3]]; !ok {
+			err = fmt.Errorf("Unknown timeunit %s", elems[3])
+			return
+		}
+		fallthrough
+	case 2: // Only start time
+		if c.Start, err = time.ParseInLocation(timefmt, elems[0]+" "+elems[1], time.UTC); err != nil {
+			return
+		}
+	default:
+		err = errors.New("Unknown schedule format")
+	}
+
+	return
+}
+
+type MultiSchedule []Schedule
+
+func (mc MultiSchedule) NextAfter(t time.Time) time.Time {
+	var nearest time.Time
+
+	for _, c := range mc {
+		next := c.NextAfter(t)
+		if next.IsZero() {
+			continue
+		}
+
+		if nearest.IsZero() {
+			nearest = next
+		} else if next.Before(nearest) {
+			nearest = next
+		}
+	}
+
+	return nearest
+}
+
+func (mc MultiSchedule) String() (s string) {
+	sep := ""
+
+	for _, c := range mc {
+		s += sep + c.String()
+		sep = "\n"
+	}
+
+	return
+}
+
+func ParseMultiSchedule(s string) (mc MultiSchedule, err error) {
+	parts := strings.Split(s, "\n")
+	for l, _part := range parts {
+		part := strings.TrimSpace(_part)
+		if part == "" {
+			continue
+		}
+
+		c, err := ParseSchedule(part)
+		if err != nil {
+			return nil, fmt.Errorf("Line %d: %s", l+1, err)
+		}
+
+		mc = append(mc, c)
+	}
+
+	return
+}