type RecurrenceWeekday = "MO" | "TU" | "WE" | "TH" | "FR" | "SA" | "SU";

/** A nonempty selection of weekdays for a weekly recurrence. */
export type RecurrenceWeekdays = {
	[Day in RecurrenceWeekday]?: true;
} & {
	[Day in RecurrenceWeekday]: Required<Pick<Record<RecurrenceWeekday, true>, Day>>;
}[RecurrenceWeekday];

export type MonthlyWeekdayOccurrence = "1st" | "2nd" | "3rd" | "4th" | "last";

export type MonthlyRecurrenceRestriction =
	| { type: "day_of_month"; day: number }
	| {
			type: "weekday_of_month";
			weekday: RecurrenceWeekday;
			occurrence: MonthlyWeekdayOccurrence;
	  };

export type RecurrenceScheduleEnd =
	| { type: "date"; endsAt: string }
	| { type: "occurrences"; count: number };

type RecurrenceScheduleBase = {
	interval: number;
	start: string;
	timeZone: string;
	end?: RecurrenceScheduleEnd;
};

export type HourlyRecurrenceSchedule = RecurrenceScheduleBase & {
	frequency: "hour";
};

export type DailyRecurrenceSchedule = RecurrenceScheduleBase & {
	frequency: "day";
};

export type WeeklyRecurrenceSchedule = RecurrenceScheduleBase & {
	frequency: "week";
	weekdays: RecurrenceWeekdays;
};

export type MonthlyRecurrenceSchedule = RecurrenceScheduleBase & {
	frequency: "month";
	monthlyRestriction: MonthlyRecurrenceRestriction;
};

export type YearlyRecurrenceSchedule = RecurrenceScheduleBase & {
	frequency: "year";
};

export type RecurrenceSchedule =
	| HourlyRecurrenceSchedule
	| DailyRecurrenceSchedule
	| WeeklyRecurrenceSchedule
	| MonthlyRecurrenceSchedule
	| YearlyRecurrenceSchedule;