Vending Machine

vending_machine.coffee

class VendingMachine

  constructor: ->
    @products = {
      'coke': 5,
      'iced tea': 5
    }
    @balance = 0

  getCount: (productName)->
    @products[productName]
    
  addMoney: (currency)->
    @balance += currency if currency > 0

  getBalance: ->
    @balance

  buy: (product) ->
    unless @balance > 0 && @products[product]
      return null

    @balance--
    @products[product]--
    return product

  demandChange: ->
    change = @balance
    @balance = 0
    change

vending_machine.js

(function() {
  var VendingMachine;
  VendingMachine = (function() {
    function VendingMachine() {
      this.products = {
        'coke': 5,
        'iced tea': 5
      };
      this.balance = 0;
    }
    VendingMachine.prototype.getCount = function(productName) {
      return this.products[productName];
    };
    VendingMachine.prototype.addMoney = function(currency) {
      if (currency > 0) {
        return this.balance += currency;
      }
    };
    VendingMachine.prototype.getBalance = function() {
      return this.balance;
    };
    VendingMachine.prototype.buy = function(product) {
      if (!(this.balance > 0 && this.products[product])) {
        return null;
      }
      this.balance--;
      this.products[product]--;
      return product;
    };
    VendingMachine.prototype.demandChange = function() {
      var change;
      change = this.balance;
      this.balance = 0;
      return change;
    };
    return VendingMachine;
  })();
}).call(this);

vending_machine_spec.coffee

describe 'A vending machine', ->

  beforeEach ->
    @m = new VendingMachine

  it 'returns product count', ->
    expect(@m.getCount('coke')).toEqual(5)

  it 'returns iced tea count', ->
    expect(@m.getCount('iced tea')).toEqual(5)

  it 'accepts money', ->
    @m.addMoney(100)
    expect(@m.getBalance()).toEqual 100  

    @m.addMoney(-10)
    expect(@m.getBalance()).toEqual 100

  it 'should sell us stuff', ->
    expect(@m.buy('coke')).toBe(null)

    @m.addMoney 2
    expect(@m.buy('coke')).toEqual 'coke'

    expect(@m.buy('iced tea')).toEqual 'iced tea'

    expect(@m.buy('coke')).toBe(null)

  it 'should not sell crack', ->
    @m.addMoney(1000)
    expect(@m.getBalance()).toEqual 1000
    expect(@m.buy('crack')).toBe(null)
  
  
  it 'should decrement the product count after buying', ->
    @m.addMoney(5)
    previous_count = @m.getCount('coke')
    @m.buy('coke')
    new_count = previous_count - 1
    expect(@m.getCount('coke')).toBe(new_count)

  it 'should give change', ->
    @m.addMoney(2)
    @m.buy('coke')
    expect(@m.demandChange()).toEqual 1
    expect(@m.getBalance()).toEqual 0

  it 'should just work', ->
    @m.addMoney(10)
    @m.buy('coke')
    @m.buy('iced tea')
    expect(@m.demandChange()).toEqual 8
    expect(@m.getBalance()).toEqual 0
    expect(@m.buy('coke'))