import type { Reference, Task } from 'fhir/r4';

// A plan item is a task, and it carries the plan it came from.
//
// Anything a plan asks the patient to do reaches them as a task, in the same attention list they
// already read - which is deliberate rather than convenient: the overview, the task modal, the outcome
// vocabulary and the notifications all need no new concepts, and a recurring plan item uses the
// recurrence that already exists.
//
// THE ONE LINE IT CARRIES THAT THE OTHERS DO NOT is the plan it came from. A plan item arrives beside
// reminders, forms and appointment prep; without that line the patient is asked to weigh themselves
// with no idea it is part of the plan their clinician built, and no route to the rest of it. The task
// is the only place that connection is visible, because the plan does not appear in the attention list.

/**
 * The plan this task came from, or `undefined` for an ordinary task.
 *
 * SEARCHED RATHER THAN INDEXED. `basedOn` already carries the appointment binding, so a plan item has
 * more than one entry and the plan is not necessarily first - taking `[0]` would silently find nothing
 * on exactly the tasks this exists for.
 */
export const getTaskCarePlanReference = (task: Task | undefined): Reference | undefined =>
    (task?.basedOn ?? []).find((reference) => reference.reference?.startsWith('CarePlan/'));

/** Whether to draw the plan line. False for the reminders and forms the patient already gets. */
export const isPlanItem = (task: Task | undefined): boolean =>
    getTaskCarePlanReference(task) !== undefined;

/** The plan's id, for the control that opens it. */
export const getTaskCarePlanId = (task: Task | undefined): string | undefined =>
    getTaskCarePlanReference(task)?.reference?.split('/')[1];