import type { Location, Schedule } from 'fhir/r4';
import { todayIn } from './initialScheduleHorizon';
import { locationTimeZoneOf } from './practiceTimezone';

/**
 * The last day a practitioner's hours run to, when that falls within `days` of today. Each schedule is
 * measured against today where it runs, so `todayFor` answers per schedule. Undefined while any
 * schedule is open-ended, runs beyond the window, or has no time zone.
 */
const plusDays = (date: string, days: number): string => {
    const next = new Date(`${date}T00:00:00Z`);
    next.setUTCDate(next.getUTCDate() + days);
    return next.toISOString().slice(0, 10);
};

export const hoursEndingSoon = (
    schedules: Schedule[], practitionerId: string, todayFor: (schedule: Schedule) => string | null, days = 30,
): string | undefined => {
    const mine = schedules.filter((schedule) => schedule.active !== false
        && (schedule.actor ?? []).some((actor) => actor.reference === `Practitioner/${practitionerId}`));
    const spans = mine.map((schedule) => ({ end: schedule.planningHorizon?.end?.slice(0, 10), today: todayFor(schedule) }));
    if (!spans.length || spans.some(({ end, today }) => !end || !today || end > plusDays(today as string, days))) return undefined;
    const running = spans.filter(({ end, today }) => (end as string) >= (today as string)).map(({ end }) => end as string);
    return running.sort()[running.length - 1];
};

/** Today where a schedule runs: its site's zone first, then the practice's, null when neither is set. */
export const todayWhereScheduleRuns = (
    schedule: Schedule, locations: Location[], practiceZone: string | null, now = new Date(),
): string | null => {
    const siteIds = (schedule.actor ?? []).map((actor) => actor.reference ?? '').filter((ref) => ref.startsWith('Location/')).map((ref) => ref.slice(9));
    const site = locations.find((location) => location.id && siteIds.includes(location.id) && locationTimeZoneOf(location));
    const zone = locationTimeZoneOf(site) ?? practiceZone;
    return zone ? todayIn(zone, now) : null;
};