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

/**
 * WHETHER A PATIENT MAY OPEN A BRAND-NEW THREAD WITH THIS PRACTITIONER.
 *
 * Spencer, 2026-09-04: a practitioner may say whether patients can direct message them, and it "would only
 * be for patients sending a brand new message to the practitioner on their own, if a practitioner messages
 * the patient then the patient should still be able to reply back."
 *
 * THE SERVER IS THE GATE; THIS IS THE EXPLANATION. `Communication/thread` refuses a patient-initiated
 * thread with somebody who has turned this off, and it would refuse one this file wrongly offered. What
 * this decides is what the patient is TOLD - and Spencer ruled that they are told plainly rather than shown
 * a door that then refuses:
 *
 *   "When the toggle is set to not allowed patients should see a message saying '[practitioner name] does
 *    not currently accept new messages' and disable the click event on them. If they already have a message
 *    thread with the practitioner then this doesn't apply and clicking the practitioner would open up the
 *    existing thread like normal."
 *
 * SO THE ROW HAS THREE STATES, NOT TWO, and the middle one is the one that gets lost: a practitioner who
 * declines NEW threads but is already in a conversation with this patient stays fully clickable. Greying
 * out every listing of them satisfies the toggle and breaks the ruling - the patient can still post a reply
 * but can no longer reach the thread to write it in.
 *
 * READ FROM THE PROJECTED PAYLOAD. The patient's copy of a Practitioner is reduced to a directory view and
 * `extension` is an open container that is dropped whole; this one url is named back into it server-side
 * precisely so this rule can be answered here. If that naming is ever removed, every practitioner reads as
 * accepting - which is the failure direction chosen deliberately below.
 */
export const PATIENT_INITIATED_MESSAGES_EXTENSION =
    'https://akashichealthrecords.com/fhir/extensions/patient-initiated-messages';

/**
 * May a patient start a new conversation with this practitioner?
 *
 * FAILS OPEN, matching its server twin exactly - the two must agree, and if they disagree the server wins
 * and the patient sees a door that refuses. Only an explicit `valueBoolean === false` closes it; absent,
 * malformed, or the wrong value type all read as open, which is also the default this ships with.
 */
export const allowsPatientInitiatedMessages = (
    practitioner: Practitioner | undefined | null,
): boolean => {
    const setting = (practitioner?.extension ?? []).find(
        (extension) => extension.url === PATIENT_INITIATED_MESSAGES_EXTENSION,
    );

    return setting?.valueBoolean !== false;
};

/** The sentence the patient sees in place of a door. Named so the copy has one home. */
export const declinesNewMessagesNotice = (practitionerName: string | undefined): string =>
    `${practitionerName?.trim() || 'This person'} does not currently accept new messages`;

/**
 * The three states a practitioner's row can be in on the patient's provider picker.
 *
 * NAMED AS A RULE BECAUSE THE MIDDLE ONE IS THE ONE THAT GETS LOST. `open` and `declined` are the pair
 * anybody would write from the toggle alone; `existing` is the exception Spencer attached to it, and a
 * build that greys out every listing of a practitioner who declines satisfies the toggle and breaks the
 * ruling - the patient can still post a reply but can no longer reach the thread to write it in.
 *
 * A rule that cannot be stated on its own cannot be tested on its own, and this one has to be.
 */
export type PatientPickerRowState = 'open' | 'existing' | 'declined';

export const patientPickerRowState = (
    practitioner: Practitioner | undefined | null,
    hasExistingThread: boolean,
): PatientPickerRowState => {
    if (allowsPatientInitiatedMessages(practitioner)) return 'open';

    // Checked SECOND and deliberately: an existing conversation outranks the setting, because the setting
    // governs starting one and this one has already started.
    return hasExistingThread ? 'existing' : 'declined';
};