class StateMachine {
  constructor() {
    this.state = 'idle';
    this.transitions = {
      idle: { start: 'running', reset: 'idle' },
      running: { pause: 'paused', stop: 'stopped' },
      paused: { resume: 'running', stop: 'stopped' },
      stopped: { reset: 'idle' }
    };
  }
  
  transition(action) {
    const nextState = this.transitions[this.state]?.[action];
    if (nextState) {
      this.state = nextState;
      return true;
    }
    return false;
  }
}

const sm = new StateMachine();
console.log(sm.transition('start'));
console.log(sm.state);
console.log(sm.transition('reset'));
console.log(sm.state);

const target = { name: 'Sarah', age: 25 };
const handler = {
  get(obj, prop) {
    if (prop === 'toString') {
      return () => `Person: ${obj.name}`;
    }
    return Reflect.get(obj, prop);
  },
  has(obj, prop) {
    return prop !== 'age' && Reflect.has(obj, prop);
  }
};
const proxy = new Proxy(target, handler);
console.log(proxy.name);
console.log('age' in proxy);
console.log(proxy.toString());

async function processData() {
  console.log('Start');
  
  const promise1 = new Promise(resolve => {
    console.log('Promise 1 executor');
    resolve('Result 1');
  });
  
  const promise2 = Promise.resolve('Result 2');
  console.log('After promises created');
  
  const result1 = await promise1;
  console.log(result1);
  
  const result2 = await promise2;
  console.log(result2);
  
  return 'Done';
}

processData().then(result => console.log(result));

console.log('1');

Promise.resolve().then(() => {
  console.log('2');
  Promise.resolve().then(() => console.log('3'));
});

Promise.resolve().then(() => {
  console.log('4');
});

setTimeout(() => console.log('5'), 0);

console.log('6');

function processData() {
  try {
    console.log('processing');
    return 'success';
  } catch (error) {
    console.log('error caught');
    return 'failed';
  } finally {
    console.log('cleanup');
  }
}

const result = processData();
console.log('result:', result);

class EventEmitter {
  constructor() { this.events = {}; }
  on(event, fn) { (this.events[event] ||= []).push(fn); }
  emit(event, data) { this.events[event]?.forEach(fn => fn(data)); }
}

class Logger {
  log(msg) { console.log(`LOG: ${msg}`); }
}

class Counter {
  constructor() { this.count = 0; }
  increment() { this.count++; console.log(this.count); }
}

function withLogging(target) {
  const logger = new Logger();
  return new Proxy(target, {
    get(obj, prop) {
      if (typeof obj[prop] === 'function') {
        return function(...args) {
          logger.log(`calling ${prop}`);
          return obj[prop].apply(obj, args);
        };
      }
      return obj[prop];
    }
  });
}

const emitter = withLogging(new EventEmitter());
const counter = new Counter();
emitter.on('tick', () => counter.increment());
emitter.emit('tick');
emitter.emit('tick');

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

class Dog extends Animal {
  speak() {
    return super.speak() + ' and barks';
  }
}

const pet = new Dog('Rex');
console.log(pet.speak());
console.log(pet instanceof Animal);
console.log(pet.constructor.name);