new_context.rb

class CreateUser < Context
  def initialize(attributes)
    @attributes = attributes
  end

  def self.call(*args)
    new(*args).tap(&:call)
  end

  def callback(*args)
    # execute CallbackProxy
  end

  def call
    user = User.create!(@attributes)
    if with_team?
      team = Team.create!(:leader => user)
      success.user_created_with_team(user, team)
    else
      success.user_created(user)
    end
  rescue ActiveRecord::RecordInvalid => e
    failure.user_invalid e, e.record
  end

  def success
    # Record via CallbackProxy
  end

  def failure
    # Record via CallbackProxy
  end

  class CallbackProxy
    def method_missing(method, *args)
      @methods << [ methods, args ]
    end

    def execute(callback)
      @methods.each do |method, args|
        callback.public_send(method, *args)
      end
    end
  end
end


class UserMailer
  def user_created(user)
  end

  def user_created_with_team(user, team)
  end
end

class UserError
  def user_invalid(error)
  end

  def lfp_sucks(error)
  end
end

CreateUser.call(user_id).callback SendUserMail.new, UserError.new
CreateUser.call(user_id).callback UserMailer.new
CreateUser.call(user_id).callback :success => SendUserMail.new, :failure => UserError.new


CreateUser.call(user_id).callback do |success, failure|
  success.user_created do |user|
  end
  success.user_created_with_team do |user|
  end
  failure.user_invalid do |error|
  end
end