# Sometimes complex read operations might deserve their own objects, Policy Object is the right solution.
# Policy Objects are similar to Service Objects, but it is conventional to use services for write operations
# and policies for read.
# They are also similar to Query Objects, but Query Objects focus on executing SQL to return a result set,
# whereas Policy Objects operate on domain models already loaded into memory.
# app/policies/twitter_policy.rb

class TwitterPolicy < Struct.new(:auth)

  def first_name
    auth['info']['name'].split(' ').first
  end

  def last_name
   .....
  end

  ....
end


# app/policies/facebook_policy.rb
class FacebookPolicy < Struct.new(:auth)
  def first_name
    auth['info']['first_name']
  end

  def last_name
   .....
  end

  ....
end

# app/models/user.rb
def self.from_oauth(auth)  
  policy = "#{auth['provider']}_policy".classify.constantize.new(auth)
  create_user_from_policy(policy)
end

# Check https://github.com/elabs/pundit for maximum usage of policies and OO design
# Pundit: Minimal authorization through OO design and pure Ruby classes