ski forum\

class Forum {
    constructor() {
        this._users = [];
        this._questions = [];
        this.id = 1;
        this.loggedUsers = [];
    }

    register(username, password, repeatPassword, email) {
        const usernameCheck = this._users.find((o) => { return o.email === email || o.username === username });

        if (!username || !password || !repeatPassword || !email) {
            throw Error("Input can not be empty");
        }

        if (password !== repeatPassword) {
            throw Error("Passwords do not match");
        }

        if (usernameCheck) {
            throw Error('This user already exists!');
        }

        this._users.push({ username, password, email });

        return `${username} with ${email} was registered successfully!`

    }

    login(username, password) {
        const usernameCheck = this._users.find((o) => { return o.password === password || o.username === username });

        if (!usernameCheck) {
            throw Error("There is no such user");
        } else {
            this.loggedUsers.push(username);
            return "Hello! You have logged in successfully";
        }
    }

    logout(username, password) {
        const usernameCheck = this._users.find((o) => { return o.password === password || o.username === username });

        if (!usernameCheck) {
            throw Error("There is no such user");
        } else {
            let index = this.loggedUsers.indexOf(username);
            this.loggedUsers.splice(index, 1);
            return "You have logged out successfully";
        }
    }

    postQuestion(username, question) {
        const usernameCheck = this._users.find((o) => { return o.username === username });

        if (!this.loggedUsers.includes(username) || !usernameCheck) {
            throw Error("You should be logged in to post questions");
        }

        if (!question) {
            throw Error("Invalid question");
        }

        this._questions.push({ username, question, id: this.id, answer: [] });
        this.id++;
    }

    postAnswer(username, questionId, answer) {
        const usernameCheck = this._users.find((o) => { return o.username === username });
        const idCheck = this._questions.find((o) => { return o.id === questionId });
        if (!this.loggedUsers.includes(username) || !usernameCheck) {
            throw Error("You should be logged in to post answers");
        }

        if (!answer) {
            throw Error("Invalid answer");
        }

        if (!idCheck) {
            throw Error("There is no such question");
        }

        idCheck.answer.push([username, answer]);

        return "Your answer has been posted successfully";
    }

    showQuestions() {
        let result = [];

        for (const line of this._questions) {
            result.push(`Question ${line.id} by ${line.username}: ${line.question}`)

            for (const x of line.answer) {
                result.push(`---${x.shift()}: ${x.shift()}`);
            }
        }
        return result.join('\n');
    }
}