/** Today as YYYY-MM-DD in a time zone, so a practice in Chicago does not start tomorrow at 7pm. */
export const todayIn = (timeZone: string, now: Date = new Date()): string =>
    new Intl.DateTimeFormat('en-CA', { timeZone, year: 'numeric', month: '2-digit', day: '2-digit' }).format(now);

/**
 * A new clinician's first schedule: from today for 12 calendar months, ending the day before the
 * anniversary. It is bounded because the overlap check cannot compare an open-ended schedule.
 */
export const initialScheduleHorizon = (today: string): { start: string; end: string } => {
    const [year, month, day] = today.split('-').map(Number);
    const anniversary = new Date(Date.UTC(year + 1, month - 1, day));
    // A 29 February start has no anniversary date; Date rolls to 1 March, so the day before is 28 February.
    anniversary.setUTCDate(anniversary.getUTCDate() - 1);
    return { start: today, end: anniversary.toISOString().slice(0, 10) };
};

/** A schedule date for a sentence, e.g. 23 September 2027, day first like formatDayMonthYear. */
export const formatScheduleDate = (date: string): string =>
    new Date(`${date}T12:00:00Z`).toLocaleDateString('en-GB', { month: 'long', day: 'numeric', year: 'numeric', timeZone: 'UTC' });