first version

internal/timeutil/clock.go

@@ -0,0 +1,93 @@
+package timeutil
+
+import (
+	"fmt"
+	"time"
+)
+
+type Clock interface {
+	Now() time.Time
+	Sleep(ctxDone <-chan struct{}, d time.Duration) bool
+}
+
+type RealClock struct {
+	Loc *time.Location
+}
+
+func (c RealClock) Now() time.Time {
+	now := time.Now()
+	if c.Loc != nil {
+		return now.In(c.Loc)
+	}
+	return now
+}
+
+func (c RealClock) Sleep(ctxDone <-chan struct{}, d time.Duration) bool {
+	timer := time.NewTimer(d)
+	defer timer.Stop()
+	select {
+	case <-timer.C:
+		return true
+	case <-ctxDone:
+		return false
+	}
+}
+
+type TimeOfDay struct {
+	Duration time.Duration
+}
+
+func ParseTimeOfDay(raw string) (TimeOfDay, error) {
+	parsed, err := time.Parse("15:04:05", raw)
+	if err != nil {
+		return TimeOfDay{}, fmt.Errorf("parse time of day %q: %w", raw, err)
+	}
+	return TimeOfDay{
+		Duration: time.Duration(parsed.Hour())*time.Hour +
+			time.Duration(parsed.Minute())*time.Minute +
+			time.Duration(parsed.Second())*time.Second,
+	}, nil
+}
+
+func (t *TimeOfDay) UnmarshalText(text []byte) error {
+	parsed, err := ParseTimeOfDay(string(text))
+	if err != nil {
+		return err
+	}
+	*t = parsed
+	return nil
+}
+
+func (t TimeOfDay) String() string {
+	total := int64(t.Duration.Seconds())
+	h := total / 3600
+	m := (total % 3600) / 60
+	s := total % 60
+	return fmt.Sprintf("%02d:%02d:%02d", h, m, s)
+}
+
+func (t TimeOfDay) On(date time.Time, loc *time.Location) time.Time {
+	local := date.In(loc)
+	y, m, d := local.Date()
+	midnight := time.Date(y, m, d, 0, 0, 0, 0, loc)
+	return midnight.Add(t.Duration)
+}
+
+type Window struct {
+	Start TimeOfDay
+	End   TimeOfDay
+}
+
+func (w Window) Contains(now time.Time, loc *time.Location) bool {
+	start := w.Start.On(now, loc)
+	end := w.End.On(now, loc)
+	return !now.Before(start) && now.Before(end)
+}
+
+func Drift(local, server time.Time) time.Duration {
+	d := local.Sub(server)
+	if d < 0 {
+		return -d
+	}
+	return d
+}