transforms vs ifs

0_README.md

I was changing the behaviour of this controller, and wondered if there was some way to make it less branchy and more self-documenenting.

I remembered an idea of Dave Thomas's - thinking about programs as series of transforms - and tried to apply it.

Which do you prefer?

1_with_ifs.rb

class OauthController < ApplicationController
  # creates a new external service every time, and removes old, to ensure
  # we capture any updated information from user trusting us with more
  def create
    existing_service = ExternalService.find_with_oauth(auth)

    user = nil

    if signed_in?

      # a new or updated oauth for the current user
      user = current_user

    else

      # a signup, or login
      user = if existing_service
               existing_service.user
             else
               User.create_with_oauth(auth)
             end

      sign_in(user)

    end

    ExternalService.create_or_update_with_oauth(auth, user, existing_service)
    redirect_to home_url

  end

  private

  def auth
    request.env['omniauth.auth']
  end
end

2_transforms.rb

class OauthController < ApplicationController
  # creates a new external service every time, and removes old, to ensure
  # we capture any updated information from user trusting us with more
  def create
    existing_service = ExternalService.find_with_oauth(auth)
     
    user = case authorisation_state(existing_service)
           when :logged_in
             current_user
           when :login
             existing_service.user
           when :signup
             User.create_with_oauth(auth)
           end

    ExternalService.create_or_update_with_oauth(auth, user, existing_service)
    sign_in(user)
    redirect_to home_url
  end

  private

  def authorisation_state existing_service
    if signed_in?
      :logged_in
    else
      existing_service ? :login : :signup
    end
  end

  def auth
    request.env['omniauth.auth']
  end
end