console.log('1: start');

setTimeout(() => console.log('2: setTimeout'), 0);

Promise.resolve()
  .then(() => {
    console.log('3: promise 1');
    return Promise.resolve('chained');
  })
  .then((val) => console.log(`4: ${val}`));

queueMicrotask(() => console.log('5: microtask'));

new Promise((resolve) => {
  console.log('6: executor');
  resolve();
}).then(() => console.log('7: promise 2'));

console.log('8: end');

class BankAccount {
  #balance;
  #transactionHistory = [];

  constructor(initialBalance) {
    this.#balance = initialBalance;
  }

  deposit(amount) {
    this.#balance += amount;
    this.#transactionHistory.push(`+${amount}`);
    return this;
  }

  withdraw(amount) {
    this.#balance -= amount;
    this.#transactionHistory.push(`-${amount}`);
    return this;
  }

  get summary() {
    return `Balance: ${this.#balance} | Transactions: ${this.#transactionHistory.join(", ")}`;
  }

  static hasPrivateBalance(obj) {
    return #balance in obj;
  }
}

const account = new BankAccount(100);
account.deposit(50).deposit(25).withdraw(30);

console.log(account.summary);
console.log(BankAccount.hasPrivateBalance(account));
console.log(BankAccount.hasPrivateBalance({}));

class EventEmitter {
  #listeners = new Map();

  on(event, listener) {
    if (!this.#listeners.has(event)) {
      this.#listeners.set(event, []);
    }
    this.#listeners.get(event).push(listener);
    return this;
  }

  emit(event, ...args) {
    const handlers = this.#listeners.get(event) ?? [];
    handlers.forEach(fn => fn(...args));
    return this;
  }

  once(event, listener) {
    const wrapper = (...args) => {
      listener(...args);
      this.off(event, wrapper);
    };
    return this.on(event, wrapper);
  }

  off(event, listener) {
    const updated = (this.#listeners.get(event) ?? []).filter(fn => fn !== listener);
    this.#listeners.set(event, updated);
    return this;
  }
}

const emitter = new EventEmitter();
const log = [];

emitter.on("data", val => log.push(`on:${val}`));
emitter.once("data", val => log.push(`once:${val}`));
emitter.on("data", val => log.push(`on2:${val}`));

emitter.emit("data", "A");
emitter.emit("data", "B");

console.log(log.join(", "));

function makeCounter(start = 0, step = 1) {
  let count = start;
  const history = [];

  return {
    increment() {
      count += step;
      history.push(count);
      return this;
    },
    decrement() {
      count -= step;
      history.push(count);
      return this;
    },
    getHistory: () => history,
    getCount: () => count,
  };
}

const counter = makeCounter(10, 3);
counter.increment().increment().decrement();

console.log(counter.getCount());
console.log(counter.getHistory());

const delay = (ms) => new Promise((resolve) => setTimeout(resolve, ms));

async function processQueue(items) {
  const results = [];

  await items.reduce(async (prevPromise, item) => {
    await prevPromise;
    await delay(0);
    results.push(item * 2);
  }, Promise.resolve());

  return results;
}

processQueue([1, 2, 3, 4])
  .then((data) => console.log("Result:", data))
  .catch((err) => console.log("Error:", err.message));

Promise.resolve()
  .then(() => console.log("Microtask A"))
  .then(() => console.log("Microtask B"));

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

const item = "sword";
const qty = 3;
const price = 9.5;

const output = highlight`You bought ${qty} ${item}s for $${price} each.`;
console.log(output);