import type { Appointment, Extension } from 'fhir/r4';

// The catalogue service a booking chose, beside its clinical coding. The server reads the same
// URL: one top-level Appointment.extension holding a plain local HealthcareService reference.
export const SELECTED_SERVICE_EXTENSION_URL = 'https://akashichealthrecords.com/fhir/StructureDefinition/appointment-healthcare-service';

/** The appointment with exactly this selected service; every other extension is kept. */
export function withSelectedServiceRef<T extends Pick<Appointment, 'extension'>>(appointment: T, serviceId: string): T {
    const others = (appointment.extension ?? []).filter((extension) => extension.url !== SELECTED_SERVICE_EXTENSION_URL);
    const selected: Extension = { url: SELECTED_SERVICE_EXTENSION_URL, valueReference: { reference: `HealthcareService/${serviceId}` } };
    return { ...appointment, extension: [...others, selected] };
}

/** The id of the one catalogue service this booking recorded choosing, if it recorded exactly one. */
export function selectedServiceIdOf(appointment: Pick<Appointment, 'extension'> | undefined): string | undefined {
    const carried = (appointment?.extension ?? []).filter((extension) => extension.url === SELECTED_SERVICE_EXTENSION_URL);
    if (carried.length !== 1) return undefined;
    return /^HealthcareService\/([A-Za-z0-9\-.]{1,64})$/.exec(carried[0].valueReference?.reference ?? '')?.[1];
}