const user = {
  profile: {
    settings: {
      theme: 'dark',
      notifications: null
    }
  }
};

const result1 = user?.profile?.settings?.theme;
const result2 = user?.profile?.settings?.notifications?.email;
const result3 = user?.profile?.preferences?.language ?? 'en';
const result4 = user?.profile?.settings?.notifications?.push?.('test');

console.log(result1, result2, result3, result4);

const original = {
  name: 'Sarah',
  hobbies: ['reading', 'coding'],
  address: { city: 'Portland', zip: 97201 }
};

const shallow = { ...original };
const deep = JSON.parse(JSON.stringify(original));

shallow.name = 'Emma';
shallow.hobbies.push('hiking');
shallow.address.city = 'Seattle';

deep.hobbies.push('swimming');
deep.address.zip = 98101;

console.log(original.hobbies.length, original.address.city);

class SimpleObservable {
  constructor(subscribeFn) {
    this.subscribeFn = subscribeFn;
  }
  
  subscribe(observer) {
    return this.subscribeFn(observer);
  }
}

const obs = new SimpleObservable(observer => {
  observer.next('first');
  observer.next('second');
  observer.complete();
});

const results = [];
obs.subscribe({
  next: val => results.push(val),
  complete: () => results.push('done')
});

console.log(results.join('-'));

const arr = [1, 2, 3];
const obj = { valueOf: () => 4, toString: () => '5' };
const result1 = arr + obj;
const result2 = +obj;
const result3 = String(obj);
const result4 = obj == 4;
const result5 = obj === 4;
console.log(`${result1}|${result2}|${result3}|${result4}|${result5}`);
const weird = [] + [] + 'hello';
const weirder = [] + {} + [];
const weirdest = {} + [] + {};
console.log(`${weird}|${weirder}|${weirdest}`);
const final = !!'0' + !!'' + !!null + !!undefined;
console.log(final);

const data = '{"users": [{"name": "Sarah", "age": 25}, {"name": "Mike", "age": null}]}';

try {
  const parsed = JSON.parse(data);
  const result = parsed.users.map(user => {
    return user.age ?? 'unknown';
  });
  console.log(result.join(' - '));
} catch (error) {
  console.log('Parse error occurred');
}

const invalidJson = '{"name": "John", age: 30}';
try {
  JSON.parse(invalidJson);
  console.log('Success');
} catch {
  console.log('Invalid');
}

class Logger {
  log(msg) {
    return `[LOG]: ${msg}`;
  }
}

class Formatter {
  format(text) {
    return text.toUpperCase();
  }
}

class Service {
  constructor(logger, formatter) {
    this.logger = logger;
    this.formatter = formatter;
  }
  
  process(data) {
    const formatted = this.formatter.format(data);
    return this.logger.log(formatted);
  }
}

const service = new Service(new Logger(), new Formatter());
console.log(service.process('hello world'));

let obj1 = { name: 'Sarah' };
let obj2 = { name: 'Mike' };

obj1.ref = obj2;
obj2.ref = obj1;

let weakRef = new WeakRef(obj1);
let registry = new FinalizationRegistry((value) => {
  console.log(`Cleanup: ${value}`);
});

registry.register(obj1, 'obj1-cleaned');
obj1 = null;
obj2 = null;

console.log(weakRef.deref()?.name || 'undefined');
console.log('Script completed');

class EventEmitter {
  constructor() {
    this.events = {};
  }
  
  on(event, callback) {
    this.events[event] = this.events[event] || [];
    this.events[event].push(callback);
    return this;
  }
  
  emit(event, data) {
    if (this.events[event]) {
      this.events[event].forEach(cb => cb(data));
    }
    return this;
  }
}

const emitter = new EventEmitter();
emitter.on('test', x => console.log(x * 2))
       .on('test', x => console.log(x + 5))
       .emit('test', 10);