Pure example

purevsimpure.rb

class Cafe
  class NotSufficientMoney < StandardError
  
  def self.charge(user_id,amount)
      user = User.find(user_id)
      raise NotSufficientMoney if user.balance < amount
      tax = amount * 0.7
      Debit.create!(user, amount + tax)
   end
 end
 
 
 #More Pure version
 
class Cafe
  class NotSufficientMoney < StandardError
  
  def self.charge(user_id,amount)
      user = User.find(user_id)
      raise NotSufficientMoney if user_does_not_have_enough_money?(user.balance, amount)
      Debit.create!(user, amount + calculate_tax_for(amount))
   end
   
   def user_does_not_have_enough_money?(balance, amount)
     balance < amount
   end
   
   def calculate_tax_for(amount)
     amount * 0.7
   end
 end