import type { Questionnaire, QuestionnaireItem, QuestionnaireResponse } from 'fhir/r4';
import { answeredQuestions } from './questionnaireAnswerText';
import { changedAnswers } from './changedAnswers';
import { QUESTIONNAIRE_HIDDEN_URL } from './loincUncomputedTotals';

/**
 * The most questions a form may have and still be answered inside the task dialog. A longer one
 * opens on its own page, where the patient can come back to it.
 */
export const LONGEST_FORM_ANSWERED_IN_PLACE = 12;

const isHidden = (item: QuestionnaireItem): boolean =>
    (item.extension ?? []).some((extension) => extension.url === QUESTIONNAIRE_HIDDEN_URL && extension.valueBoolean === true);

/** The questions a patient can answer: every item they can see but headings and the groups that hold others. */
const visibleQuestionIds = (questionnaire: Pick<Questionnaire, 'item'> | undefined): Set<string> => {
    const ids = new Set<string>();
    const walk = (items: QuestionnaireItem[] | undefined) => {
        for (const item of items ?? []) {
            if (isHidden(item)) continue;
            if (item.type !== 'display' && item.type !== 'group') ids.add(item.linkId);
            walk(item.item);
        }
    };

    walk(questionnaire?.item);
    return ids;
};

export const countQuestions = (questionnaire: Pick<Questionnaire, 'item'> | undefined): number =>
    visibleQuestionIds(questionnaire).size;

export const isLongForm = (questionnaire: Pick<Questionnaire, 'item'> | undefined): boolean =>
    countQuestions(questionnaire) > LONGEST_FORM_ANSWERED_IN_PLACE;

/** How many of the questions the patient can see the response answers; a stored hidden answer never counts. */
export const countAnswered = (
    response: QuestionnaireResponse | undefined,
    questionnaire: Pick<Questionnaire, 'item'> | undefined,
): number => {
    const visible = visibleQuestionIds(questionnaire);
    return new Set(answeredQuestions(response).map((entry) => entry.linkId).filter((id) => visible.has(id))).size;
};

export const describeProgress = (answered: number, total: number): string => `${answered} of ${total} answered`;

const joinNames = (names: string[]): string =>
    names.length < 2 ? names.join('') : `${names.slice(0, -1).join(', ')} and ${names[names.length - 1]}`;

/** The changed questions by name, so the patient can see which answers moved. */
export const describeChangedQuestions = (
    current: QuestionnaireResponse | undefined,
    previous: QuestionnaireResponse | undefined,
): string | undefined => {
    const names = changedAnswers(current, previous)
        .filter((entry) => entry.changed)
        .map((entry) => `“${entry.question.trim()}”`);

    if (!names.length) {
        return undefined;
    }

    return `You changed ${names.length} ${names.length === 1 ? 'answer' : 'answers'}: ${joinNames(names)}.`;
};