import type { Reference, Schedule } from 'fhir/r4';

// S4 - reading a block's Location actors when there can be MORE THAN ONE.
//
// A Schedule now carries the practitioner's physical site AND, when the block offers video, the org's
// virtual (telehealth) Location. That co-actor arrangement is what makes a video booking share the
// block's existing slot pool instead of forking it into a second Schedule.
//
// THE BUG THIS EXISTS TO FIX: `ScheduleService.getScheduleLocationReference` is `.find(...)` - the
// FIRST Location actor only. The patient booking flow derived its entire `locationIds` accessor from it,
// so a block carrying [physical, virtual] reported ONLY the physical one and the telehealth gate then
// raised NO_VIRTUAL_LOCATION_ON_BLOCK for a block that had explicitly opted into video. Patient video
// booking was impossible. (The staff context was already correct - it filters all Location actors.)
//
// Lives here rather than beside the singular reader because `ScheduleService.tsx` cannot be imported by
// a test: it pulls in `environment.ts`, which throws at module load outside the app. A pure module is
// the difference between this rule being pinned by tests and not.
//
// The singular reader is deliberately NOT changed. Plenty of callers legitimately want "the location of
// this block" for a label or a single-select, and it remains exactly `getScheduleLocationReferences(s)[0]`.

/** EVERY `Location/` actor on the schedule, in actor order. */
export const getScheduleLocationReferences = (schedule?: Schedule): Reference[] =>
    (schedule?.actor ?? []).filter((ref) => ref.reference?.startsWith('Location/'));

/** Their bare ids, for the accessors that compare against a location id. */
export const getScheduleLocationIds = (schedule?: Schedule): string[] =>
    getScheduleLocationReferences(schedule)
        .map((ref) => ref.reference?.split('/').pop())
        .filter((id): id is string => Boolean(id));

/**
 * The Location a block should be LABELLED with, which is not simply its first actor.
 *
 * Spencer ruled on 2026-09-14 that a block whose only location is virtual is a VIDEO-ONLY block,
 * and that a pattern which is both in person and by video names its site. That makes the label
 * load-bearing: it is the only place a reader is told which of the two shapes a block is.
 *
 * THE FIRST ACTOR IS THE WRONG ANSWER FOR THAT QUESTION. `buildScheduleLocationActors` writes
 * [physical, virtual], so first-actor happens to be right for anything saved through the current
 * editor - but it is right by accident of ORDER, and any block whose stored order puts the virtual
 * one first reads as "Video Visit" while it is genuinely bookable at a site. One exists on the
 * staging practice today. Under the ruling that is no longer a cosmetic mislabel: it tells the
 * reader the block is video only when it is not.
 *
 * So the label is derived from the RULING - the physical site if there is one, the virtual one only
 * when there is nothing else - rather than from the order the actors happen to sit in.
 *
 * `virtualLocationId` undefined means the practice has no virtual Location, so nothing can be
 * virtual and the first actor is the whole answer.
 */
export const scheduleLocationLabelRef = (
    schedule: Schedule | undefined,
    virtualLocationId: string | undefined,
): Reference | undefined => {
    const refs = getScheduleLocationReferences(schedule);
    if (!virtualLocationId) return refs[0];
    const physical = refs.find((ref) => ref.reference !== `Location/${virtualLocationId}`);
    return physical ?? refs[0];
};

/**
 * Which site to SEED the block editor's location picker with.
 *
 * THE ROLE FALLBACK IS FOR BLOCKS THAT PREDATE THE MOVE, when location lived on the
 * PractitionerRole rather than on the block. Those carry no Location actor at all, and seeding
 * from the role is how they keep working.
 *
 * IT MUST NOT REACH A VIDEO-ONLY BLOCK. Such a block DOES carry a Location actor - the virtual
 * one - and deliberately carries no site, which since Spencer's 2026-09-14 ruling is a meaningful
 * shape rather than an omission. Letting the role fallback fire there seeds the picker with a
 * hospital the block is not at, tells the administrator the wrong thing, and - because the save
 * writes whatever the picker holds - silently converts a video-only block into a site-plus-video
 * one on any save that did not touch the field.
 *
 * Measured on the staging practice: a Sunday video-only block opened reading "West Burlington
 * Hospital" while the same dialog's own summary, and the schedules list, both read "Video Visit".
 *
 * THE DISTINCTION IS WHETHER THE BLOCK NAMES ANY LOCATION AT ALL, not whether it names a site.
 */
export const seedScheduleLocationId = (
    schedule: Schedule | undefined,
    virtualLocationId: string | undefined,
    roleLocationId: string | undefined,
): string => {
    const ids = getScheduleLocationIds(schedule);
    const physical = ids.find((id) => id !== virtualLocationId);
    if (physical) return physical;

    // It named its locations and none of them is a site: that is the video-only shape, and an
    // empty picker is the truth about it.
    if (ids.length > 0) return '';

    // Hours on the Schedule mean it was saved after the move, so no Location is "All locations".
    const ownsHours = (schedule?.extension ?? []).some((ext) =>
        /\/schedule-(available-time|not-available)$/.test(ext.url));
    if (ownsHours) return '';

    return roleLocationId ?? '';
};