Introduction

Welcome to the code review for RPS Challenge! Again, don't worry - you are not expected to have all the answers. The following is a code-review scaffold for RPS Challenge that you can follow if you want to. These are common issues to look out for in this challenge - but you may decide to take your own route.

If you don't feel comfortable giving technical feedback at this stage, try going through this guide with your reviewee and review the code together.

Step 0: Checkout and Run tests

Please checkout your reviewee's code and run their tests. Read the code and try and play the game through the web interface. You can also experiment with the engine in IRB. How easy is it to understand the structure of their code? How readable is their code? Did you need to make any cognitive leaps to 'get it'?

Step 1: Structure and supporting files

Instructions in README

As we have seen previously, the README is a great place to show the full story of how your app is used (from a user's perspective). For a web app, include instructions for how to download and run the app, e.g.:

$ git clone git@github.com:[USERNAME]/rps-challenge.git
$ cd rps-challenge
$ bundle
$ rackup

And maybe include some screenshots? For more info on embedding images in a README: https://guides.github.com/features/mastering-markdown/

e.g.:

![Screenshot](https://path_to_your_image)

You will need to host your images somewhere, e.g.:

http://imgur.com/
http://dropbox.com/

Inconsistent folder layout (Sinatra structure)

Sinatra is not a particularly opinionated framework (unlike Rails). This means it does not mandate folder structures and naming conventions. This gives developers the freedom to choose their own structures according to the needs of a project.

Structure is an important decision in your design as it affects readability. One of the most important considerations is the separation of concerns

Here is a checklist to consider:

If the structure has an `/app` folder:

Is the server file (e.g rps_web.rb or app.rb) at the top level of the /app folder?
Is the /views folder in /app?
Is the /lib folder in the project root folder?

├── app
│   └── rps_web.rb
│   └── views
│       └── index.erb
├── lib
│   ├── game.rb
│   ├── computer.rb
│   └── player.rb
└── spec
    └── spec_helper.rb

If the structure does not have an `/app` folder:

Is the server file (e.g rps_web.rb or app.rb) in the project root folder?

├── lib
│   ├── game.rb
│   ├── computer.rb
│   └── player.rb
├── spec
│   └── spec_helper.rb
├── views
│   └── index.erb
└── rps_web.rb

Inconsistent file naming

Ruby class files should be named with the snake_case version of the class name. Class names should be PascalCase. Hence:

Good

class RPS -> rps.rb
class RPSWeb -> rps_web.rb

Bad

class RPS_web -> rps_web.rb
class RPSWeb -> rps.rb

Not initializing capybara/ spec_helper correctly

In spec/spec_helper.rb, don't forget to add Capybara.app = MyRackApp or similar. There are gems which can generate your test setup for you but beware that the spec_helper will be overwritten; make sure you copy all the pre-written CI code, otherwise you will break your coveralls CI, causing silent failure of your pull request.

Not removing commented-out code before committing

Old code should be deleted before you commit - it is distracting and makes your code hard to read. There is no reason to keep commented-out code - if you are commiting regularly, all your code will be in git so you can easily look back at how it looked before you made changes.

Step 2: Tests and *_spec.rb files

*_spec.rb files (unit tests)

Not testing all of the game logic in unit tests

As there is a discrete number of possible outcomes, your tests should test them all. This may seem like overkill, but how else will you know that your game logic is correct in all circumstances?

*_spec.rb files (feature tests)

Testing game logic in feature tests

Your feature test should not need to test all of the rock/paper/scissors(/lizard/spock) possibilities - this is the responsibility of your unit tests.

Not testing all game outcomes in feature tests

Although you do not need to test all possible combinations, your feature tests should test every possible outcome - i.e.:

a win
a loss
and a draw.

to ensure the user interface logic is correct.

Stub out random behaviour

stub out random behaviour to ensure your feature tests pass consistently, e.g. (i)

feature 'Playing the game' do
  scenario "When I submit 'Rock' I am told if I have won" do
    allow_any_instance_of(Array).to receive(:sample).and_return('scissors')
    visit '/'
    fill_in('name', with: 'Philip')
    select('rock', from: 'your_choice')
    click_button('Play')
    expect(page).to have_content "The result is .... You won"
  end
end

Step 3: Application code and *.rb files

Including presentation strings in business logic layer

Your Game class (or similar) should not return presentation strings like "Congratulations - you won!". This is a presentation concern and should be handled in another layer of code (separation of concerns). Instead, return representative codes, such as :win and :draw from the Game class which can be translated by the presentation layer.

This approach makes it possible to change the presentation layer (e.g. to add support for a different language) without changing the lower-level code (open/closed principle).

bad

class Game
  def result
    'Congratulations - you won!'
  end
end

class RPSWeb < Sinatra::Application
  get '/result' do
    @game = Game.new
    erb :result
  end
end

<h1><%= @game.result%></h1>

good

class Game
  def result
    :win # hard coded for example purposes
  end
end

class RPSWeb < Sinatra::Application
  get '/result' do
    @game = Game.new
    erb @game.result
  end
end

in views/win.erb:

<h1>Congratulations - you won</h1>

Use of `if/elsif` conditionals for business logic

Long if and elsif trees are very difficult to read and nested if statements require too much working memory for a reader to quickly scan.

There are a number of approaches to the game logic of Rock Paper Scissors, e.g.:

Use a hash to map the rules:

RULES = { rock: :scissors,
          paper: :rock,
          scissors: :paper }

or for RPSLS:

RULES = { rock: [scissors, lizard],
          paper: [:rock, :spock],
          scissors: [:paper, :lizard],
          lizard: [:paper, :spock],
          spock: [:rock, :scissors] }

Use a Weapon class with a beats? or similar method that takes another weapon instance as a parameter.

class Weapon
  attr_reader :type

  def initialize(type)
    @type = type.to_sym
  end

  def beats?(other)
    RULES[type][other.type]
  end
end

rock = Weapon.new(:rock)
rock.beats?(Weapon.new(:scissors))

Not encapsulating the 'computer' in a separate class

By creating a Computer class, you can take advantage of duck-typing in the game class. The game does not need to know if it's comparing two players or one player vs a computer or even two computers!

class Computer
  def weapon
    [:rock, :paper, :scissors].sample
  end
end

class Player
  attr_reader :weapon

  def weapon=(weapon)
    fail 'not a possible weapon' unless [:rock, :paper, :scissors].includes? weapon
    @weapon = weapon
  end
end

Use of global variables

It is tempting to use global variables to ensure instances of a game or players are persisted across calls to the server. But global variables are evil. There are a number of other ways to achieve the same thing. While some may argue these also introduce 'globally accessible' state, the critical difference is we have more control over this state and it is properly namespaced. Here is an example using a class methods inside the server and Sinatra helper methods to encapsulate the interface:

class Player

  # class methods

  def self.find(id)
    players[id]
  end

  def self.add(id, player)
    players[id] = player
  end

  def self.players
    @players ||= {}
  end

  # instance methods

  attr_reader :name

  # ... other instance methods
end

class RPSWeb < Sinatra::Application
  enable :sessions

  helpers do
    def current_player
      Player.find(session[:player_id])
    end

    def add_player(player)
      id = player.object_id
      Player.add(id, player)
      session[:player_id] = id
    end
  end

  get '/' do
    "Hello #{current_player.name}" if current_player
  end

  post '/player' do
    player = Player.new(params[:name])
    add_player(player)
    redirect_to '/'
  end
end

Not storing the weapons in a constant

If you have something like this:

def weapons
  ['Rock', 'Paper', 'Scissors']
end

Then four new objects will be created every time you call weapons (what are the four objects?). Use a constant with symbols instead:

WEAPONS = [:rock, :paper, :scissors]

Inconsistent routing and route naming

Routes should not have dual purposes. Each discrete action of your programme should have its own dedicated route (N.B. the route comprises both the verb and the path).

The preferred convention for naming routes is snake_case, e.g. game over Game.

class RPSWeb < Sinatra::Application

  get '/game' do
    erb :new_game
  end

  post '/game' do
    @game = Game.new(params)
    redirect to '/play'
  end
end

In the above example the first route GETs the form that allows a user to create a new game. This action does not change any state on the server so it's important that we use the GET action, and not POST. The second route corresponds to the POSTed submission of the new game form. This action does create some state on the server, i.e. the creation of a particular game, so it makes sense to use the active verb POST here.

Defining weapons in more than one place

Don't Repeat Yourself (DRY)! The list of available weapons should be defined in only one place. It can be passed around or referenced or injected, but not duplicated!

Let's DRY the code from the encapsulation example above:

class Game
  WEAPONS = [:rock, :paper, :scissors]
end

class Computer
  def weapon
    Game::WEAPONS.sample
  end
end

class Player
  attr_reader :weapon

  def weapon=(weapon)
    fail 'not a possible weapon' unless Game::WEAPONS.includes? weapon
    @weapon = weapon
  end
end

Calling business logic from the view

It is the controller's responsibility to pass the player's weapon to the game and get the result. Use instance variables or helper methods to represent or convert this result for rendering in the view.

bad

class Game
  def result
    :win
  end
end

class RPSWeb < Sinatra::Application
  get '/choose' do
    @player1_choice = params[:choice]
    @game = Game.current_game(session[:game_id])
    erb :result
  end
end

<h1>
<% @game.player1_choice(@player1_choice) %>
<% if @game.result == :win %>
  Congratulations - you won
<% else %>
  Sorry - you lost
<% end %>
</h1>

better

class Game
  def result
    :win
  end
end

class RPSWeb < Sinatra::Application
  get '/choose' do
    @game.player1_choice(params[:choice])
    erb @game.result
  end
end

in views/win.erb:

<h1>Congratulations - you won</h1>

Fat controllers

Game logic should be executed in your lib files. You should minimise the amount of logic in the controller by extracting it to the lib files. This helps to ensure your code is testable, maintainable and reusable.

bad

class RPSWeb < Sinatra::Application
  get '/choose' do
    @player_choice = params[:choice]
    @computer_choice = [:rock, :scissors, :paper].sample
    @result = 'you lose!'
    if RULES[@player_choice][@computer_choice]
      @result = 'you win!'
    end
    erb :result
  end
end

<h1><%= @result %></h1>

better

class Game
  WEAPONS = [:rock, :paper, :scissors]
  def player_choice=(weapon)
    fail 'not a possible weapon' unless WEAPONS.includes? weapon
    @player_choice = weapon
  end
  def result
    RULES[player_choice][computer.choice()] ? :win : :lose
  end
end

class RPSWeb < Sinatra::Application
  get '/play' do
    @game.player1_choice = params[:choice]
    erb @game.result
  end
end

in views/win.erb:

<h1>Congratulations - you won</h1>

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review.md

review.md

Introduction

Step 0: Checkout and Run tests

Step 1: Structure and supporting files

Instructions in README

Inconsistent folder layout (Sinatra structure)

If the structure has an `/app` folder:

If the structure does not have an `/app` folder:

Inconsistent file naming

Good

Bad

Not initializing capybara/ spec_helper correctly

Not removing commented-out code before committing

Step 2: Tests and *_spec.rb files

*_spec.rb files (unit tests)

Not testing all of the game logic in unit tests

*_spec.rb files (feature tests)

Testing game logic in feature tests

Not testing all game outcomes in feature tests

Stub out random behaviour

Step 3: Application code and *.rb files

Including presentation strings in business logic layer

Use of `if/elsif` conditionals for business logic

Not encapsulating the 'computer' in a separate class

Use of global variables

Not storing the weapons in a constant

Inconsistent routing and route naming

Defining weapons in more than one place

Calling business logic from the view

Fat controllers

Files

review.md

Latest commit

History

review.md

File metadata and controls

Introduction

Step 0: Checkout and Run tests

Step 1: Structure and supporting files

Instructions in README

Inconsistent folder layout (Sinatra structure)

If the structure has an /app folder:

If the structure does not have an /app folder:

Inconsistent file naming

Good

Bad

Not initializing capybara/ spec_helper correctly

Not removing commented-out code before committing

Step 2: Tests and *_spec.rb files

*_spec.rb files (unit tests)

Not testing all of the game logic in unit tests

*_spec.rb files (feature tests)

Testing game logic in feature tests

Not testing all game outcomes in feature tests

Stub out random behaviour

Step 3: Application code and *.rb files

Including presentation strings in business logic layer

Use of if/elsif conditionals for business logic

Not encapsulating the 'computer' in a separate class

Use of global variables

Not storing the weapons in a constant

Inconsistent routing and route naming

Defining weapons in more than one place

Calling business logic from the view

Fat controllers

If the structure has an `/app` folder:

If the structure does not have an `/app` folder:

Use of `if/elsif` conditionals for business logic