import type { Communication } from 'fhir/r4';
import { looksLikeAnIdentifier, senderLabel } from './senderLabel';

// A message a related person writes for a patient anchors to the patient (sender = Patient/{id}) and the
// SERVER stamps who really wrote it, from the writer's own act-as identity; a copy on the request is dropped.
// So this reads only that stamp, never the sender's display, which the writing client supplies.
export const SENT_ON_BEHALF_BY_URL = 'https://akashichealthrecords.com/fhir/StructureDefinition/sent-on-behalf-by';

// helperReference is the stamped writer, compared by identity; two helpers may share a name.
export type OnBehalfOf = { helperReference: string; helperName: string; patientName?: string };

export const onBehalfOf = (
    communication: Communication,
    rosterNames?: Record<string, string | undefined>,
): OnBehalfOf | undefined => {
    const stamp = communication.extension?.find((extension) => extension?.url === SENT_ON_BEHALF_BY_URL);
    if (!stamp?.valueReference?.reference?.startsWith('RelatedPerson/')) return undefined;

    const named = (stamp.valueReference.display ?? '').trim();
    // The patient by reference, from the roster: the sender's display is the writing client's word. Left
    // unnamed when the roster cannot say, so the caller can use the thread's own counterparty.
    const patient = senderLabel({ display: undefined, reference: communication.sender?.reference, rosterNames });
    return {
        helperReference: stamp.valueReference.reference,
        helperName: named && !looksLikeAnIdentifier(named) ? named : 'Their helper',
        ...(patient !== 'Participant' ? { patientName: patient } : {}),
    };
};