// The period a report row was counted over, carried to the list it opens: its days are the practice's,
// on the clock the report used, never the viewer's.
import { addCalendarDays, calendarDateInZone, zonedWallClockToInstant } from './practiceTimezone';

export interface DrillPeriod { from: string; to: string; zone: string }

const DAY = /^[0-9]{4}-[0-9]{2}-[0-9]{2}$/;

const knownZone = (zone: string) => {
    try {
        new Intl.DateTimeFormat('en-US', { timeZone: zone });
        return true;
    } catch {
        return false;
    }
};

export const drillPeriodParams = (filters: { start: string; end: string }, zone: string) => ({ start: filters.start, end: filters.end, tz: zone });

export const drillPeriodFrom = (params: URLSearchParams): DrillPeriod | null => {
    const from = params.get('start');
    const to = params.get('end');
    const zone = params.get('tz');
    if (!from || !to || !zone || !DAY.test(from) || !DAY.test(to) || from > to || !knownZone(zone)) return null;
    return { from, to, zone };
};

/** The instant a calendar day begins on the given clock, for a server-side search bound. */
export const dayStartIn = (day: string, zone: string): string => zonedWallClockToInstant(day, '00:00', zone).toISOString();

/** A FHIR `date` search covering the period's days on its clock: from the first day's midnight, before the day after the last. */
export const drillPeriodDateSearch = (period: DrillPeriod): string[] =>
    ['ge' + dayStartIn(period.from, period.zone), 'lt' + dayStartIn(addCalendarDays(period.to, 1), period.zone)];

export const withinDrillPeriod = (instant: string | undefined, period: DrillPeriod): boolean => {
    if (!instant) return false;
    const at = new Date(instant);
    if (Number.isNaN(at.getTime())) return false;
    const day = calendarDateInZone(at, period.zone);
    return day >= period.from && day <= period.to;
};