Printify interview

vending-machine.ts

import * as assert from 'assert';

const coins = [1, 2, 5, 10, 20, 50, 100, 200].reverse();

type Coins = Map<number, number>;

interface Product {
  name: string;
  price: number;
}

class Machine {
  constructor(private readonly products: Product[]) {
  }

  buy(productName: string, coins: Coins): { coins: Coins, product: Product } {
    const product = this.getProduct(productName);
    const amount = this.countCoins(coins);
    if (amount < product.price) {
      throw new Error('Not enough money');
    }

    return {
      product,
      coins: Machine.getChange(amount - product.price)
    };
  }

  private getProduct(name: string) {
    const product = this.products.find((p) => p.name == name);
    if (!product) {
      throw new Error('No such product');
    }
    return product;
  }

  private countCoins(coins: Coins): number {
    let amount = 0;
    coins.forEach((count, coinPrice) => {
      amount += count * coinPrice;
    })
    return amount;
  }

  static getChange(amount: number): Coins {
    const change = new Map();

    for (let i = 0; i < coins.length; i++) {
      const q = Math.floor(amount / coins[i]);
      if (q >= 1) {
        change.set(coins[i], q);
        amount -= coins[i] * q;
      }
      if (!amount) {
        break;
      }
    }

    return change;
  }
}


// Unit tests
assert.deepEqual(Machine.getChange(500), new Map([[200, 2], [100, 1]]));
assert.deepEqual(Machine.getChange(105), new Map([[100, 1], [5, 1]]));
assert.deepEqual(Machine.getChange(0), new Map());

console.log('\n\nUNIT TESTS PASSED\n\n')


// Integrations
const machine = new Machine([
  {name: 'Knachapury', price: 233},
  {name: 'B', price: 126},
  {name: 'C', price: 95},
]);


// it should throw on unknown product
assert.throws(
  () => {
    machine.buy('Cola', new Map([[200, 1]]));
  },
  {
    name: 'Error',
    message: 'No such product'
  }
);

// it should throw if user inserts not enough money
assert.throws(
  () => {
    machine.buy('Knachapury', new Map([[200, 1]]));
  },
  {
    name: 'Error',
    message: 'Not enough money'
  }
);

// it should return product and change
assert.deepEqual(machine.buy('Knachapury', new Map([[200, 2]])), {
  product: {name: 'Knachapury', price: 233},
  coins: new Map([[100, 1], [50, 1], [10, 1], [5, 1], [2, 1]])
});

console.log('\n\nINTEGRATION TESTS PASSED\n\n')