import type { Location, PractitionerRole, Reference, Schedule } from 'fhir/r4';
import { onlySites } from '../roomLocation';
import { getScheduleLocationReferences } from '../scheduleLocations';

/**
 * The PHYSICAL site a schedule's hours are written in, from the Location references it carries.
 *
 * - THIS IS THE INPUT TO THE PRACTICE'S CLOCK, which is why "first reference" is not good
 * enough. `resolveBookingTimeZone` takes a site and falls back to the organization, and a video-enabled
 * block carries **two** Location actors - the physical site and the org's virtual one. Taking
 * `location[0]` hands a telehealth block the virtual Location, which has no clock of its own (that is
 * what makes it virtual), so the zone silently falls through to the organization's.
 *
 * Right by luck for a single-site practice, and wrong for the exact case the clock work exists for -
 * a west-coast patient booking an east-coast therapist. Sites only, always.
 *
 * EXTRACTED because both booking flows had already written these five lines independently and two more
 * callers were about to. A derivation with a documented trap in it, copied four times, is a trap that
 * only gets fixed in three places.
 *
 * It takes REFERENCES rather than a Schedule on purpose: resolving a schedule's references to the role
 * fallback lives in the flows (a block saved before location moved onto the Schedule carries it on the
 * PractitionerRole), and importing that here would point a util at a service.
 *
 * `undefined` is a real answer - an "all locations" block names no site, and the caller then correctly
 * falls back to the organization's zone.
 */
export const firstPhysicalSite = (
    locationRefs: Reference[] | undefined,
    locationsList: Location[] | undefined,
): Location | undefined =>
    onlySites(
        (locationRefs ?? [])
            .map((ref) =>
                (locationsList ?? []).find((loc) => loc.id === ref.reference?.split('/').pop()),
            )
            .filter((loc): loc is Location => Boolean(loc)),
    )[0];

/**
 * The same answer, straight from a schedule and its owning role.
 *
 * THE ROLE FALLBACK IS NOT OPTIONAL: a block saved before `location` moved onto the Schedule carries
 * it on the `PractitionerRole` instead. Dropping it reads those blocks as "all locations" and quietly
 * puts every one of them on the organization's clock.
 *
 * Both booking flows already wrote this pair of lines locally; this is the same derivation with the
 * trap documented once. Only `getScheduleLocationReferences` is imported - a pure util - so nothing here
 * points at a service.
 */
export const scheduleSiteFor = (
    schedule: Schedule | undefined,
    role: PractitionerRole | undefined,
    locationsList: Location[] | undefined,
): Location | undefined => {
    const scheduleRefs: Reference[] = schedule ? getScheduleLocationReferences(schedule) : [];
    // A video-only block names only the virtual Location, which has no clock: its hours are kept on
    // the clinician's site, else the practice's only site, before the organization's (often unset) zone.
    const soleSite = onlySites(locationsList ?? []);
    return firstPhysicalSite(scheduleRefs, locationsList)
        ?? firstPhysicalSite(role?.location, locationsList)
        ?? (soleSite.length === 1 ? soleSite[0] : undefined);
};