03. Ski Forum-26 October 2019- exam

class SkiForum {

  #users = [];
  #questions = [];
  #id = 1;

  register(username, password, repeatPassword, email) {
      if (!(username && password && repeatPassword && email)) {
          throw new Error("Input can not be empty");
      }

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

      if (this.findUser(username)) {
          throw new Error("This user already exists!");
      }

      const user = {
          username,
          password,
          email
      }

      this.#users.push(user);

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

  login(username, password) {
      const user = this.findUser(username);

      if (!user) {
          throw new Error("There is no such user")
      }

      if (user.password === password && !user.isLoggedIn) {
          user.isLoggedIn = true;
          return "Hello! You have logged in successfully";
      }
  }

  logout(username, password) {
      const user = this.findUser(username);

      if (!user) {
          throw new Error("There is no such user")
      }

      if (user.password === password && user.isLoggedIn) {
          user.isLoggedIn = false;
          return "You have logged out successfully";
      }
  }

  postQuestion(username, question) {
      const user = this.findUser(username);

      if (!user || !user.isLoggedIn) {
          throw new Error("You should be logged in to post questions");
      }

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

      this.#questions.push(
          {
              id: this.#id,
              author: username,
              question,
              answers: []
          }
      )

      this.#id++;

      return `Your question has been posted successfully`;
  }

  postAnswer(username, questionId, answer) {
      const user = this.findUser(username);

      if (!user || !user.isLoggedIn) {
          throw new Error("You should be logged in to post answers");
      }

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

      const question = this.#questions.find(q => q.id === questionId);

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

      question.answers.push({author: username, answer});

      return `Your answer has been posted successfully`;
  }

  showQuestions() {
      let result = '';
      this.#questions.forEach(element => {
          result += `Question ${element.id} by ${element.author}: ${element.question}\n`;

          element.answers = element.answers.map(e => `---${e.author}: ${e.answer}`);
          result += element.answers.join('\n') + '\n';
      });

      return result.trim();
  }

  findUser(username) {
      return this.#users.find(u => u.username === username);
  }
}