bmelnychuk

const questionGenerationPolicy = new RandomNextQuestionPolicy();
const answerValidationPolicy = new TextEqualityAnswerValidationPolicy();
const questionRepository = new QuestionStoreRepository();

const getNextQuestionUseCase = new GetNextQuestion(
    questionRepository, questionGenerationPolicy
);
const answerQuestionUseCase = new AnswerQuestion(
    questionRepository, answerValidationPolicy

bmelnychuk

import { getQuestions, getQuestion } from '../../../question-store';

export default class QuestionStoreRepository implements QuestionRepository {
    async getAvailableQuestions(categoryId: string): Promise<Question[]> {
        const rawQuestions = await getQuestions(categoryId);
        return rawQuestions.map(rawQuestion => new Question(
            rawQuestion.id,
            rawQuestion.question,
            rawQuestion.answer
        ));

bmelnychuk

...
export function getQuestions(categoryId: string): Promise<{ id: string, question: string, answer: string}[]>
export function getQuestion(questionId: string): Promise<{ id: string, question: string, answer: string}>
...

bmelnychuk

class TextEqualityAnswerValidationPolicy implements AnswerValidationPolicy {
    isAnswerValid(userAnswer: string, correctAnswer: string): Promise<boolean> {
        return Promise.resolve(
            userAnswer.trim().toLowerCase() === correctAnswer.toLowerCase()
        );
    }
}

bmelnychuk

class RandomNextQuestionPolicy implements NextQuestionPolicy {
    async getNextQuestion(availableQuestions: Question[]): Promise<Question> {
        if (availableQuestions.length === 0) 
            throw new Error('Next question is not available');
        
        const nextRandomIndex = RandomNextQuestionPolicy.getRandomInt(
            0, availableQuestions.length - 1
        );
        return Promise.resolve(availableQuestions[nextRandomIndex]);
    }

bmelnychuk

class AnswerResult {
    userAnswer: string;
    isValid: boolean;
    correctAnswer: string;
}

class AnswerQuestion {
    questionRepository: QuestionRepository;
    answerValidationPolicy: AnswerValidationPolicy;

bmelnychuk

class GetNextQuestion {
    questionRepository: QuestionRepository;
    nextQuestionPolicy: NextQuestionPolicy;

    async invoke(categoryId: string): Promise<Question> {
        const availableQuestions = await this.questionRepository.getAvailableQuestions(
            categoryId
        );
        return this.nextQuestionPolicy.getNextQuestion(availableQuestions);
    }

bmelnychuk

interface QuestionRepository {
    getAvailableQuestions(categoryId: string): Promise<Question[]>;
    getById(questionId: string): Promise<Question>;
}

bmelnychuk

interface NextQuestionPolicy {
    getNextQuestion(availableQuestions: Question[]): Promise<Question>;
}

bmelnychuk

interface AnswerValidationPolicy {
    isAnswerValid(userAnswer: string, correctAnswer: string): Promise<boolean>;
}