chain of resp.js

class ShoppingCart {

  constructor() {
    this.products = [];
  }

  addProduct(p) {
    this.products.push(p);
  };
}

class Discount {

  calc(products) {
    let ndiscount = new NumberDiscount();
    let pdiscount = new PriceDiscount();
    let none = new NoneDiscount();
    ndiscount.setNext(pdiscount);
    pdiscount.setNext(none);
    return ndiscount.exec(products);
  };
}

class NumberDiscount {

  constructor() {
    this.next = null;
  }

  setNext(fn) {
    this.next = fn;
  };

  exec(products) {
    let result = 0;
    if (products.length > 3)
      result = 0.05;

    return result + this.next.exec(products);
  };
}

class PriceDiscount {

  constructor() {
    this.next = null;
  }

  setNext(fn) {
    this.next = fn;
  };

  exec(products) {
    let result = 0;
    let total = products.reduce((a, b) => a + b);

    if (total >= 500)
      result = 0.1;

    return result + this.next.exec(products);
  };
}

class NoneDiscount {
  exec() {
    return 0;
  };
}

export {
  ShoppingCart,
  Discount
};