encoach_frontend/src/utils/exams.be.ts

import { groupBy, shuffle } from "lodash";
import { CEFRLevels, Exam, InstructorGender, SpeakingExam, Variant, WritingExam } from "@/interfaces/exam";
import { DeveloperUser, Stat, StudentUser, User } from "@/interfaces/user";
import { Module } from "@/interfaces";
import { Db } from "mongodb";
import client from "@/lib/mongodb";
import { MODULE_ARRAY } from "./moduleUtils";
import { mapBy } from ".";
import { getUser } from "./users.be";

const db = client.db(process.env.MONGODB_DB);

export async function getSpecificExams(ids: string[]) {
	if (ids.length === 0) return [];

	const exams: Exam[] = (
		await Promise.all(
			MODULE_ARRAY.flatMap(
				async (module) =>
					await db
						.collection(module)
						.find<Exam>({ id: { $in: ids } })
						.toArray(),
			),
		)
	).flat();

	return exams;
}

export const getExam = async (module: Module, id: string) => {
	return await db.collection(module).findOne<Exam>({ id }) ?? undefined
};

export const getExamsByIds = async (ids: { module: Module; id: string }[]) => {
	const groupedByModule = groupBy(ids, "module");
	const exams: Exam[] = (
		await Promise.all(
			Object.keys(groupedByModule).map(
				async (m) =>
					await db
						.collection(m)
						.find<Exam>({ id: { $in: mapBy(groupedByModule[m], 'id') } })
						.toArray(),
			),
		)
	).flat();

	return exams;
};

export const getExams = async (
	db: Db,
	module: Module,
	avoidRepeated: string,
	// added userId as due to assignments being set from the teacher to the student
	// we need to make sure we are serving exams not executed by the user and not
	// by the teacher that performed the request
	userId: string | undefined,
	variant?: Variant,
	instructorGender?: InstructorGender,
): Promise<Exam[]> => {
	const allExams = await db
		.collection(module)
		.find<Exam>({
			isDiagnostic: false,
		})
		.toArray();

	const shuffledPublicExams = shuffle(
		allExams.map((doc) => ({
			...doc,
			module,
		})) as Exam[],
	).filter((x) => !x.private);

	let exams: Exam[] = await filterByEntities(shuffledPublicExams, userId);
	exams = filterByVariant(exams, variant);
	exams = filterByInstructorGender(exams, instructorGender);
	exams = await filterByDifficulty(db, exams, module, userId);
	exams = await filterByPreference(db, exams, module, userId);

	if (avoidRepeated === "true") {
		const stats = await db
			.collection("stats")
			.find<Stat>({
				user: userId,
			})
			.toArray();

		const filteredExams = exams.filter((x) => !stats.map((s) => s.exam).includes(x.id));

		return filteredExams.length > 0 ? filteredExams : exams;
	}

	return exams;
};

const filterByInstructorGender = (exams: Exam[], instructorGender?: InstructorGender) => {
	if (!instructorGender || instructorGender === "varied") return exams;

	return exams.filter((e) => (e.module === "speaking" ? e.instructorGender === instructorGender : true));
};

const filterByVariant = (exams: Exam[], variant?: Variant) => {
	const filtered = variant && variant === "partial" ? exams.filter((x) => x.variant === "partial") : exams.filter((x) => x.variant !== "partial");
	return filtered.length > 0 ? filtered : exams;
};

const filterByEntities = async (exams: Exam[], userID?: string) => {
	if (!userID) return exams.filter((x) => !x.entities || x.entities.length === 0);

	const user = await getUser(userID)

	return await Promise.all(
		exams.filter(async (x) => {
			if (!x.entities) return true;
			if (x.entities.length === 0) return true;

			return mapBy(user?.entities || [], 'id').some(e => x.entities!.includes(e))
		}),
	);
};

const filterByDifficulty = async (db: Db, exams: Exam[], module: Module, userID?: string) => {
	if (!userID) return exams;
	const user = await db.collection("users").findOne<User>({ id: userID });
	if (!user) return exams;

	const basicDifficulty = user.levels[module] <= 3 ? "easy" : user.levels[module] <= 6 ? "medium" : "hard";

	let CEFRLevel: CEFRLevels;

	// Adjust the levels if necessary
	switch (user.levels[module]) {
		case 1:
		case 2:
			CEFRLevel = "A1";
			break;
		case 3:
		case 4:
			CEFRLevel = "A2";
			break;
		case 4:
		case 5:
			CEFRLevel = "B1";
			break;
		case 6:
			CEFRLevel = "B2";
			break;
		case 7:
		case 8:
			CEFRLevel = "C1";
			break;
		case 9:
			CEFRLevel = "C2";
			break;
		default:
			CEFRLevel = "B1";
	}

	const filteredExams = exams.filter((exam) =>
		exam.difficulty === basicDifficulty || exam.difficulty === CEFRLevel
	);

	return filteredExams.length === 0 ? exams : filteredExams;
};

const filterByPreference = async (db: Db, exams: Exam[], module: Module, userID?: string) => {
	if (!["speaking", "writing"].includes(module)) return exams;

	if (!userID) return exams;

	const user = await db.collection("users").findOne<StudentUser | DeveloperUser>({ id: userID });
	if (!user) return exams;

	if (!["developer", "student"].includes(user.type)) return exams;
	if (!user.preferredTopics || user.preferredTopics.length === 0) return exams;

	const userTopics = user.preferredTopics;
	const topicalExams = exams.filter((e) => {
		const exam = e as WritingExam | SpeakingExam;
		const topics = exam.exercises.map((x) => x.topic).filter((x) => !!x) as string[];

		return topics.some((topic) => userTopics.map((x) => x.toLowerCase()).includes(topic.toLowerCase()));
	});

	return topicalExams.length > 0 ? shuffle(topicalExams) : exams;
};