// sub-task 5a Task 9 - the PURE half of "who is in the meeting". Deliberately dependency-free
// (no service contexts, no React): `MeetingParticipantsPanel.tsx` imports these to do the actual
// fetching, but the resolution RULES live here so `meetingParticipants.test.ts` can exercise them in
// plain node without pulling in `environment.ts` (which touches `window` at module scope and only
// survives under jsdom).
//
// NEVER RENDER THE RAW REFERENCE. `Practitioner/9f2c-...` means nothing to a patient and leaks an
// internal id into a room a related person may be sitting in. Every path through `resolveParticipantLabel`
// below ends in either a real name or one of two fixed, PHI-free fallbacks.

/** The three resource types this client can actually resolve a name for - one fetch each, via their
 * own service context. Anything else (a type with no fetch available) is treated as unresolvable
 * rather than guessed at. */
export type ResolvableParticipantType = 'Practitioner' | 'Patient' | 'RelatedPerson';

export const RESOLVABLE_PARTICIPANT_TYPES: ResolvableParticipantType[] = ['Practitioner', 'Patient', 'RelatedPerson'];

/** Fallback #2's copy. Deliberately generic ("A practitioner", not a name) - this is what renders
 * when the type is known but no usable name resolved (never fetched, fetch failed, or the resource has
 * no name on file). */
export const PARTICIPANT_NEUTRAL_LABEL: Record<ResolvableParticipantType, string> = {
    Practitioner: 'A practitioner',
    Patient: 'The patient',
    RelatedPerson: 'A related person',
};

/** Splits `externalUserId` into a FHIR reference's `{ResourceType}/{id}` - and nothing further is ever
 * done with the raw string once this returns. `null` for anything that isn't a genuine two-part
 * `Type/id` shape, including an absent value; the caller reads `null` as fallback 3. */
export function parseParticipantReference(externalUserId: string | undefined): { type: string; id: string } | null {
    if (!externalUserId) return null;
    const slash = externalUserId.indexOf('/');
    if (slash <= 0 || slash === externalUserId.length - 1) return null;
    return { type: externalUserId.slice(0, slash), id: externalUserId.slice(slash + 1) };
}

/** THE THREE FALLBACKS, IN ORDER, and none may leak the raw reference:
 * 1. a resolved, non-empty name use it
 * 2. no resolvable name but a known resource type that type's neutral label
 * 3. absent/unparseable `externalUserId`, OR a type this client has no fetch for `'Someone'`
 *
 * `resolvedName` must already be `undefined` for "no usable name" - NEVER `''`. `formatFhirHumanName`
 * returns `''` for an unusable name, and `'' ?? x` is still `''` (nullish coalescing does not catch an
 * empty string) - that exact bug shipped once already and produced a window titled "Notes - ". The
 * caller converts with `||`, never `??`, before this runs. */
export function resolveParticipantLabel(
    externalUserId: string | undefined,
    resolvedName: string | undefined,
): string {
    const ref = parseParticipantReference(externalUserId);
    if (!ref) return 'Someone';
    if (resolvedName) return resolvedName;
    return RESOLVABLE_PARTICIPANT_TYPES.includes(ref.type as ResolvableParticipantType)
        ? PARTICIPANT_NEUTRAL_LABEL[ref.type as ResolvableParticipantType]
        : 'Someone';
}

/** Up to two initials from a display label, for a name card or a roster avatar. */
export const initialsOf = (label: string): string =>
    label.split(/\s+/).filter(Boolean).slice(0, 2).map((word) => word[0]).join('').toUpperCase();