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

// Prepare a video visit via the server's named operation (POST /R4/Encounter, X-Encounter-Operation: prepare-visit); the
// client enters only on `entered`, with the record returned. Deploy the server first: an older one ignores the header.
export const ENCOUNTER_OPERATION_HEADER = 'X-Encounter-Operation';
export const PREPARE_VISIT_OPERATION = 'prepare-visit';

export type PrepareVisitAnswer =
    | { result: 'entered'; how: 'created' | 'reused' | 'stamped' | 'restamped' | 'revived' | 'adopted'; encounter: Encounter; owed?: 'stamp' }
    | { result: 'visit-not-open'; owed?: 'close-open-visit-records' }
    | { result: 'generation-unproved'; reason: string; owed?: 'adopt-preparation' | 'redo-check-in'; record?: string }
    | { result: 'needs-update-authority' }
    | { result: 'record-conflict' }
    | { result: 'write-unknown' };

const RESULTS = new Set(['entered', 'visit-not-open', 'generation-unproved', 'needs-update-authority', 'record-conflict', 'write-unknown']);

/** A typed answer, and for `entered` one that carries the record to enter. Anything else is not an answer. */
export const isPrepareVisitAnswer = (body: unknown): body is PrepareVisitAnswer => {
    const result = (body as { result?: unknown } | null | undefined)?.result;
    if (typeof result !== 'string' || !RESULTS.has(result)) return false;
    if (result !== 'entered') return true;
    const encounter = (body as { encounter?: Encounter }).encounter;
    return encounter?.resourceType === 'Encounter' && typeof encounter.id === 'string';
};

export const PREPARE_VISIT_NOT_OPEN = 'This visit is no longer scheduled, so it was not opened.';
export const PREPARE_VISIT_CLOSE_RECORDS = 'Its prepared record is still open: close it from the visit\'s details (Close open visit records).';
export const PREPARE_VISIT_UNPROVED = 'Could not confirm this visit is still the one that was prepared, so it was not opened. Try again?';
export const PREPARE_VISIT_ADOPT = 'This visit\'s prepared record was made before the visit was cancelled and booked again,'
    + ' so it could not be confirmed as this booking\'s. Use it for this booking?';
export const PREPARE_VISIT_REDO_CHECK_IN = 'This visit was checked in before it was cancelled and booked again, so it was not opened.'
    + ' Ask the front desk to undo the check-in and check the patient in again, then open the visit.';
export const PREPARE_VISIT_NEEDS_EDITOR = 'This visit\'s prepared record needs updating by someone who can edit visits, so it was not opened.';
export const PREPARE_VISIT_CONFLICT = 'This visit\'s record does not match this booking, so it was not opened.';
export const PREPARE_VISIT_UNKNOWN = 'Opening this visit may already have been saved, though it is not showing yet, so it was not opened.'
    + ' Try again? Trying again finds the same visit and never makes a second one.';

/** What a person is told about an answer that does not enter, and the one explicit next step it offers, if any. */
export const prepareVisitLine = (answer: Exclude<PrepareVisitAnswer, { result: 'entered' }>):
    { message: string; next?: 'try-again' | 'adopt' } => {
    switch (answer.result) {
        case 'visit-not-open':
            return { message: answer.owed === 'close-open-visit-records' ? `${PREPARE_VISIT_NOT_OPEN} ${PREPARE_VISIT_CLOSE_RECORDS}` : PREPARE_VISIT_NOT_OPEN };
        case 'generation-unproved':
            if (answer.owed === 'adopt-preparation') return { message: PREPARE_VISIT_ADOPT, next: 'adopt' };
            if (answer.owed === 'redo-check-in') return { message: PREPARE_VISIT_REDO_CHECK_IN };
            return { message: PREPARE_VISIT_UNPROVED, next: 'try-again' };
        case 'needs-update-authority':
            return { message: PREPARE_VISIT_NEEDS_EDITOR };
        case 'record-conflict':
            return { message: PREPARE_VISIT_CONFLICT };
        case 'write-unknown':
            return { message: PREPARE_VISIT_UNKNOWN, next: 'try-again' };
    }
};