const Flyable = {
  fly() { return `${this.name} is flying`; }
};

const Swimmable = {
  swim() { return `${this.name} is swimming`; }
};

function createDuck(name) {
  return Object.assign({ name }, Flyable, Swimmable);
}

const duck = createDuck('Quackers');
console.log(duck.fly());
console.log(duck.swim());
console.log(Object.getOwnPropertyNames(duck));

class Logger {
  constructor(prefix) {
    this.prefix = prefix;
  }
  log(message) {
    console.log(`${this.prefix}: ${message}`);
  }
}

class Database {
  constructor(logger) {
    this.logger = logger;
  }
  save(data) {
    this.logger.log(`Saving ${data}`);
    return `${data}_saved`;
  }
}

const logger = new Logger('DB');
const db = new Database(logger);
const result = db.save('user');
console.log(result);

const target = { name: 'Sarah', age: 25 };

const handler = {
  get(obj, prop) {
    if (prop in obj) {
      return obj[prop];
    }
    return `Property '${prop}' not found`;
  },
  set(obj, prop, value) {
    obj[prop] = value.toString().toUpperCase();
    return true;
  }
};

const proxy = new Proxy(target, handler);
proxy.city = 'boston';
console.log(proxy.name);
console.log(proxy.city);
console.log(proxy.country);

class Counter {
  constructor(max) {
    this.max = max;
  }
  
  *[Symbol.iterator]() {
    let current = 0;
    while (current < this.max) {
      yield current++;
    }
  }
}

const counter = new Counter(3);
const result = [...counter, ...counter];
console.log(result);

const numbers = [1, 2, 3, 4, 5];

const result = numbers
  .map(n => n * 2)
  .filter(n => n > 5)
  .reduce((acc, n, index) => {
    acc.sum += n;
    acc.indices.push(index);
    return acc;
  }, { sum: 0, indices: [] });

console.log(result.sum);
console.log(result.indices);

function processData(data) {
  try {
    if (!data) {
      throw new TypeError('Data is missing');
    }
    
    const result = data.process();
    return result;
  } catch (error) {
    console.log(error instanceof ReferenceError ? 1 :
               error instanceof TypeError ? 2 :
               error instanceof SyntaxError ? 3 : 4);
  }
}

processData(null);

const obj = {
  name: 'Sarah',
  getName() {
    return this.name;
  },
  getNameArrow: () => {
    return this.name;
  }
};

const getName = obj.getName;
const getNameArrow = obj.getNameArrow;

console.log(obj.getName());
console.log(getName());
console.log(getNameArrow());
console.log(obj.getNameArrow());