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

/** Whether a patient may still change answers they have sent. They lock once the visit uses them. */
export type SubmittedAnswersState = 'amendable' | 'locked';

// The lock starts at arrival rather than completion, so an answer cannot change while a clinician reads it.
const VISIT_HAS_STARTED = new Set<Appointment['status']>([
    'arrived',
    'checked-in',
    'fulfilled',
]);

// Listed explicitly so a newly added appointment status cannot silently change the outcome.
const VISIT_DID_NOT_HAPPEN = new Set<Appointment['status']>([
    'cancelled',
    'noshow',
    'entered-in-error',
]);

/** An undefined appointment means the answers are bound to no visit, so they stay amendable. */
export const submittedAnswersState = (
    appointment?: Appointment,
): SubmittedAnswersState => {
    if (!appointment) return 'amendable';
    if (VISIT_DID_NOT_HAPPEN.has(appointment.status)) return 'amendable';

    return VISIT_HAS_STARTED.has(appointment.status) ? 'locked' : 'amendable';
};

/**
 * Whether the patient may amend now. Returns undefined while a bound appointment is still loading, so a
 * write guard can refuse until the answer is known.
 */
export const mayAmendNow = (
    hasAppointmentBinding: boolean,
    appointment: Appointment | undefined,
): boolean | undefined => {
    if (hasAppointmentBinding && !appointment) return undefined;

    return submittedAnswersState(appointment) === 'amendable';
};