Defining Conditional Types with Schema or Plain TypeScript?

type ExternalCalendarEventMap = {
  cancelled: CancelledSeminarMetadata;
  "hotel-event": HotelEventMetadata;
  "business-school": BusinessSchoolMetadata;
  "online-seminar": OnlineSeminarMetadata;
};

type ExternalCalendarEvent<
  S extends CalendarEventSourceType = CalendarEventSourceType,
> = {
  readonly source: S;
  readonly sourceId: string;
  readonly title: string;
  readonly description: string | null;
  readonly startDate: DateTime;
  readonly endDate: DateTime;
  readonly metadata: ExternalCalendarEventMap[S];
};