const obj = {
  name: "Nikola",
  greetArrow: () => {
    return `Hello, ${this?.name ?? "stranger"}!`;
  },
  greetRegular() {
    return `Hello, ${this.name}!`;
  },
  greetNested() {
    const inner = () => `Hi, ${this.name}!`;
    return inner();
  }
};

console.log(obj.greetArrow());
console.log(obj.greetRegular());
console.log(obj.greetNested());

const a = 9007199254740991n;
const b = BigInt(Number.MAX_SAFE_INTEGER);

console.log(a === b);
console.log(a + 1n);
console.log(typeof a);
console.log(a === 9007199254740991);

const config = {
  timeout: 0,
  retries: null,
  host: "",
  port: undefined,
  debug: false,
};

const timeout = config.timeout ?? 3000;
const retries = config.retries ?? 5;
const host = config.host ?? "localhost";
const port = config.port ?? 8080;
const debug = config.debug ?? true;

console.log(timeout, retries, host, port, debug);

"use strict";

function createCounter() {
  let count = 0;

  return {
    increment() { count++; },
    get value() { return count; },
    toString() { return `Counter: ${count}`; }
  };
}

const counter = createCounter();
counter.increment();
counter.increment();
counter.increment();

try {
  counter.value = 99;
} catch (e) {
  console.log(`${e.constructor.name}: ${counter}`);
}

function Animal(name) {
  this.name = name;
}

Animal.prototype.speak = function () {
  return `${this.name} makes a sound.`;
};

function Dog(name, breed) {
  Animal.call(this, name);
  this.breed = breed;
}

Dog.prototype = Object.create(Animal.prototype);
Dog.prototype.constructor = Dog;

Dog.prototype.speak = function () {
  return `${this.name} barks!`;
};

const dog = new Dog("Rex", "Labrador");

console.log(dog.speak());
console.log(dog instanceof Dog);
console.log(dog instanceof Animal);
console.log(Object.getPrototypeOf(dog) === Animal.prototype);

const person = {
  name: "Marcus",
  greet: function () {
    const inner = () => `Hello, I am ${this.name}`;
    return inner();
  },
  greetArrow: () => {
    return `Hello, I am ${this.name}`;
  },
};

const detached = person.greet;

console.log(person.greet());
console.log(person.greetArrow());
console.log(detached?.());

const transactions = [
  { type: "credit", amount: 200, category: "salary" },
  { type: "debit",  amount: 50,  category: "food" },
  { type: "debit",  amount: 30,  category: "food" },
  { type: "credit", amount: 100, category: "bonus" },
  { type: "debit",  amount: 70,  category: "transport" },
];

const summary = transactions.reduce((acc, { type, amount, category }) => {
  acc.balance += type === "credit" ? amount : -amount;
  acc.byCategory[category] = (acc.byCategory[category] ?? 0) + amount;
  acc.count[type] = (acc.count[type] ?? 0) + 1;
  return acc;
}, { balance: 0, byCategory: {}, count: {} });

console.log(summary.balance);
console.log(JSON.stringify(summary.byCategory));
console.log(JSON.stringify(summary.count));