function createUser(
  name,
  role = "viewer",
  permissions = { read: true, write: false },
  level = permissions.write ? 2 : 1
) {
  return { name, role, permissions, level };
}

const user1 = createUser("Carlos");
const user2 = createUser("Diana", "editor", { read: true, write: true });
const user3 = createUser("Eve", "admin", undefined, 5);

console.log(user1.role, user1.level);
console.log(user2.role, user2.level);
console.log(user3.role, user3.level);

const user = {
  profile: {
    name: "Marcus",
    address: {
      city: "Berlin",
      zip: "10115"
    }
  },
  getSubscription: () => ({
    plan: "pro",
    features: ["analytics", "exports"]
  })
};

const city       = user?.profile?.address?.city;
const country    = user?.profile?.address?.country?.toUpperCase();
const firstFeature = user?.getSubscription?.()?.features?.[0];
const adminRole  = user?.roles?.[0]?.name ?? "guest";

console.log(city, country, firstFeature, adminRole);

const tag = (strings, ...values) => {
  return strings.reduce((result, str, i) => {
    const value = values[i - 1];
    const transformed =
      typeof value === "number" ? value * 2 : value?.toUpperCase();
    return result + transformed + str;
  });
};

const name = "carlos";
const score = 42;
const bonus = null;

const output = tag`Player: ${name}, Score: ${score}, Bonus: ${bonus}`;
console.log(output);

const p1 = new Promise((resolve) => {
  console.log("A");
  resolve("B");
});

const p2 = p1.then((val) => {
  console.log(val);
  return "C";
});

p2.then((val) => {
  console.log(val);
});

console.log("D");

function highlight(strings, ...values) {
  return strings.reduce((result, str, i) => {
    const value = values[i - 1];
    const transformed =
      typeof value === "number"
        ? `[${value * 2}]`
        : `(${String(value).toUpperCase()})`;
    return result + transformed + str;
  });
}

const product = "widget";
const qty = 4;
const price = 12.5;

const output = highlight`Order: ${product} x${qty} @ $${price}`;
console.log(output);

function* pipeline(...fns) {
  let value = yield;
  for (const fn of fns) {
    value = yield fn(value);
  }
  return value;
}

const double  = x => x * 2;
const addTen  = x => x + 10;
const square  = x => x * x;

const gen = pipeline(double, addTen, square);

gen.next();           // prime the generator
const r1 = gen.next(3);
const r2 = gen.next(r1.value);
const r3 = gen.next(r2.value);

console.log(r1.value, r2.value, r3.value);

class Timer {
  constructor() { this.seconds = 0; }
  start() {
    this.tick = () => { this.seconds++; return this.seconds; };
    return this.tick;
  }
}

const t = new Timer();
const tick = t.start();
const obj = { seconds: 100, tick };
console.log(tick(), obj.tick(), t.seconds);