Meeting / calendar scheduler

final class TimeRange {
  private final Instant start;
  private final Instant end;

  TimeRange(Instant start, Instant end) {
    if (!start.isBefore(end)) throw new InvertedRange();
    this.start = start;
    this.end = end;
  }

  boolean overlaps(TimeRange other) {
    return start.isBefore(other.end) && other.start.isBefore(end);
  }
}

interface RecurrenceRule {
  List<TimeRange> occurrences(TimeRange window);
}

/** Weekly at a wall-clock LocalTime in a ZoneId: not DayOfWeek + Instant alone. */
class WeeklyRule implements RecurrenceRule {
  private final DayOfWeek day;
  private final LocalTime localStart; // e.g. 10:00 in the calendar's zone
  private final Duration length;
  private final ZoneId zone;
  private final LocalDate until;
  public List<TimeRange> occurrences(TimeRange window) {
    // expand LocalDate + localStart → ZonedDateTime → Instant;
    // DST: spring gap may skip/adjust; fall overlap pick offset policy
  }
}

class Calendar {
  private final List<Meeting> meetings = new ArrayList<>();
  boolean hasConflict(TimeRange range) {
    return meetings.stream().anyMatch(m -> m.occupies().overlaps(range));
  }
}

class Scheduler {
  Optional<TimeRange> findSlot(List<Calendar> people, Duration duration, TimeRange window);
}