import type { Appointment } from 'fhir/r4';
import { onViewerChange, viewerEpoch, writeThroughViewer } from './writeThroughHold';

// Records of a visit this viewer already knows (a row's Encounter, or one a Prepare named), sent with every Prepare and save
// so the server reads each by id; kept per viewer, patient and visit while the page is open, never trimmed.
export const KNOWN_ENCOUNTERS_HEADER = 'X-Visit-Known-Encounters';

export interface VisitScope {
    patientId?: string;
    appointmentId?: string;
}

const known = new Map<string, string[]>();
onViewerChange(() => known.clear());

const keyOf = ({ patientId, appointmentId }: VisitScope): string | undefined =>
    patientId && appointmentId ? [viewerEpoch(), writeThroughViewer() ?? '', patientId, appointmentId].join('|') : undefined;

export const rememberVisitRecords = (scope: VisitScope, ids: (string | undefined)[]): void => {
    const key = keyOf(scope);
    if (!key) return;
    const list = known.get(key) ?? [];
    for (const id of ids) if (id && !list.includes(id)) list.push(id);
    if (list.length > 0) known.set(key, list);
};

export const knownVisitRecords = (scope: VisitScope): string[] => {
    const key = keyOf(scope);
    return key ? [...(known.get(key) ?? [])] : [];
};

/** The visit an Appointment save is for, as the known records are kept. */
export const visitScopeOf = (appointment: Appointment): VisitScope => ({
    appointmentId: appointment.id,
    patientId: appointment.participant?.find((p) => p.actor?.reference?.startsWith('Patient/'))?.actor?.reference?.slice('Patient/'.length),
});

/** The header a save of this visit carries, when its viewer knows of any of its records. */
export const knownVisitRecordsHeader = (scope: VisitScope): Record<string, string> => {
    const ids = knownVisitRecords(scope);
    return ids.length > 0 ? { [KNOWN_ENCOUNTERS_HEADER]: ids.join(',') } : {};
};