import type { Extension, HealthcareService, PractitionerRole, Reference } from 'fhir/r4';

// Whether a service is patient-self-bookable. Byte-identical to the server contract
// (docs/appointments/practitioner-services-and-self-booking-design.md §3). ONE extension URL on three carriers -
// the carrier location determines the level:
// HealthcareService.extension org DEFAULT (absent true)
// PractitionerRole.healthcareService[i].extension practitioner OVERRIDE (absent inherit default)
// Schedule.actor[i].extension block OVERRIDE (absent inherit practitioner) [Piece C]
export const SERVICE_PATIENT_SELF_BOOKABLE_EXTENSION_URL =
    'https://akashichealthrecords.com/fhir/StructureDefinition/service-patient-self-bookable';

// Tri-state form value for the per-service practitioner control (Default / Enabled / Disabled).
export type SelfBookableChoice = 'default' | 'enabled' | 'disabled';

const readBoolExt = (extensions: Extension[] | undefined): boolean | undefined => {
    const ext = extensions?.find((e) => e.url === SERVICE_PATIENT_SELF_BOOKABLE_EXTENSION_URL);
    return ext ? ext.valueBoolean : undefined;
};

// Org default carried on the HealthcareService. Absent true (services are self-bookable unless curated off).
export const getServiceSelfBookableDefault = (service?: HealthcareService | null): boolean =>
    readBoolExt(service?.extension) ?? true;

// The explicit override (or undefined = inherit) carried on a service Reference - practitioner or block level.
export const getRefSelfBookableOverride = (ref?: Reference): boolean | undefined =>
    readBoolExt(ref?.extension);

// Tri-state form value <-> stored override boolean|undefined.
export const overrideToChoice = (override: boolean | undefined): SelfBookableChoice =>
    override === undefined ? 'default' : override ? 'enabled' : 'disabled';

export const choiceToOverride = (choice: SelfBookableChoice): boolean | undefined =>
    choice === 'default' ? undefined : choice === 'enabled';

// Rebuild a service Reference's extension array applying the chosen override, PRESERVING any other ref extensions.
// override === undefined removes the self-bookable extension (inherit); true/false writes an explicit valueBoolean.
export const applyRefSelfBookable = (ref: Reference, override: boolean | undefined): Reference => {
    const others = (ref.extension ?? []).filter((e) => e.url !== SERVICE_PATIENT_SELF_BOOKABLE_EXTENSION_URL);
    const next: Extension[] = override === undefined
        ? others
        : [...others, { url: SERVICE_PATIENT_SELF_BOOKABLE_EXTENSION_URL, valueBoolean: override }];
    const result: Reference = { ...ref };
    if (next.length) {
        result.extension = next;
    } else {
        delete result.extension;
    }
    return result;
};

// Full resolution for a (service, practitionerRole). Block override is deferred to Piece C; the caller still
// applies the block master gate (schedule-allow-patient-self-booking) on top of this.
export const resolveServiceSelfBookable = (
    service: HealthcareService | undefined,
    practitionerRole?: PractitionerRole,
): boolean => {
    const ref = (practitionerRole?.healthcareService ?? []).find(
        (r) => r.reference?.split('/').pop() === service?.id,
    );
    const practitionerOverride = getRefSelfBookableOverride(ref);
    if (practitionerOverride !== undefined) {
        return practitionerOverride;
    }
    return getServiceSelfBookableDefault(service);
};