controller.rb

# coding: utf-8
class Epd::FillOutSessionsController < EpdAreaController
  def new
    interaction = interactor :select_measurement, measurement_id: params[:measurement_id],
                                                  last_used_measurement_id: session[:last_used_measurement_id],
                                                  respondent_type: params[:respondent_type],
                                                  current_patient: @patient

    @protocols       = interaction.protocols
    @measurement     = interaction.measurement
    @questionnaires  = interaction.questionnaires
    @respondent_type = interaction.respondent_type
  end
end

interactor.rb

module Interactors
  class SelectMeasurement < Interactor

    attribute :current_patient,          Patient
    attribute :measurement_id,           Integer, default: nil
    attribute :last_used_measurement_id, Integer, default: nil
    attribute :respondent_type,          String,  default: nil

    attr_reader :protocols
    attr_reader :measurement
    attr_reader :questionnaires
    attr_reader :respondent_type

    private

    def authorized?
      true
    end

    def execute
      @protocols = query(:available_protocols_with_measurements)
      @measurement = Measurement.find_by_id(measurement_id || last_used_measurement_id)
      @measurement ||= @protocols.values.flatten.first if @protocols.values.flatten.count == 1
      if @measurement
        @questionnaires = query :available_questionnaires, measurement: @measurement,
                                                           current_patient: current_patient,
                                                           respondent_type: respondent_type
        @respondent_type = @questionnaires.current_respondent_type
      end

      self
    end
  end
end