notifications-with-chupelson.js

const LOCAL = { email: "njr@gmail.com", expiredPassword: true };

const DB = {
  preferences: { optIn: false },
  notifications: { duplicated: true, something: true, fake: false },
  bills: [1]
};

const response = (type, res, params) =>
  console.log(JSON.stringify({ response: { type, res, params } }, null, 2));

const userRepo = {
  getByEmail: () => Promise.resolve(DB)
};

const getUserBy = (email) =>
  userRepo
    .getByEmail(email)
    .then((user) => user || Promise.reject(Error("USER_NOT_FOUND")))
    .catch((error) =>
      Promise.reject(Error(error?.message || "ERROR_FETCHING_USERS"))
    );

const getNotifications = (req, res) => {
  const { params } = req;
  const {
    locals: {
      user: { email, expiredPassword }
    }
  } = res;
  const category = params?.category?.split(",");

  const extract = ({ notifications, preferences, bills }) => {
    const categories = Object.assign(notifications, {
      overdue: !!bills.length,
      marketing: preferences.optIn === "subscribed",
      security: !!expiredPassword
    });

    const select = (stack, [name, status]) => {
      const skip = !status || (category && !category.includes(name));

      return skip ? stack : stack.concat({ category: name });
    };

    return Object.entries(categories).reduce(select, []);
  };

  return getUserBy(email)
    .then((user) =>
      response("SUCCESS_GENERIC", res, { notifications: extract(user) })
    )
    .catch(({ message }) => response("ERROR_GENERIC", res, { error: message }));
};

getNotifications(
  { params: { category: "security,overdue,fake" } },
  { locals: { user: LOCAL } }
).then((notifications) => console.log({ notifications }));

// api.com/notifications => all
// api.com/notifications/overdue => [{ category: 'overdue' }]
// api.com/notifications/overdue,security => [
//  { category: 'overdue' }, { category: 'security' }
// ]