Add 3-Day Outlook generation

internal/timeutil/periods.go

@@ -24,6 +24,21 @@ func (p Period) Contains(t time.Time) bool {
 	return !t.Before(p.Start) && t.Before(p.End)
 }
 
+func (p Period) Intersection(other Period) (Period, bool) {
+	if !p.Overlaps(other) {
+		return Period{}, false
+	}
+	start := p.Start
+	if other.Start.After(start) {
+		start = other.Start
+	}
+	end := p.End
+	if other.End.Before(end) {
+		end = other.End
+	}
+	return Period{Start: start, End: end}, true
+}
+
 func ParseClock(value string) (time.Duration, error) {
 	parts := strings.Split(value, ":")
 	if len(parts) != 2 {