example.rb

# app/services/results/create_export.rb

# Service object that exports assignments, transactions, and views data (for Whatify's analysis) to csv,
# uploads to Dropbox, and notifies our CEO who runs his analysis using Stata.
# Full test coverage and easy extendability

module Results
  class CreateExport
    def initialize
      upload_spreadsheets
      send_email_reminder
      create_export
    end

    private

    def upload_spreadsheets
      spreadsheets.each { |sheet| Upload.new(sheet.filepath) }
    end

    def send_email_reminder
      ResultsMailer.results_exported.deliver_now
    end

    def create_export
      Export.create
    end

    def spreadsheets
      [
        Csv::Views.new,
        Csv::Transactions.new,
        Csv::Assignments.new,
      ]
    end
  end
end



# app/services/results/upload.rb

# Uploads file to dropbox and removes tempfile
class Results::Upload
  include HTTParty

  base_uri 'https://content.dropboxapi.com/2'

  attr_reader :path

  def initialize(path)
    @path = path
    upload_to_dropbox
    delete_tempfile
  end

  def upload_to_dropbox
    self.class.post("/files/upload", headers: headers, body: read_file)
  end

  def delete_tempfile
    File.delete(path)
  end

  private

  def headers
    {
      "Authorization" => "Bearer #{ENV['DROPBOX_KEY']}",
      "Content-Type" => "application/octet-stream",
      "Dropbox-API-Arg" => "{\"path\":\"/Experimento/Shopify/export/#{path}\"}"
    }
  end

  def read_file
    File.read(path)
  end
end



# app/services/results/csv/assignments.rb

# Queries assignments data (corresponds to price randomizations on Shopify)
module Results::Csv
  class Assignments < Base
    def filename
      'assignments'
    end

    def sql_query
      <<-SQL
      select
          exp.shop_id,
          exp.external_product_id,
          ass.start,
          lead(ass.start - interval '1 second', 1) over (order by ass.start) as date_end,
          (select var.value
              from variables var
              where var.experiment_id = ass.experiment_id and (
                  ass.assignment_index = 0 and var.name = 'price1' or
                  ass.assignment_index = 1 and var.name = 'price2')
          ) active_price
          from assignments ass
          inner join experiments exp on ass.experiment_id = exp.id
          where ass.created_at > '#{last_export}';
      SQL
    end
  end
end



# app/services/results/csv/transactions.rb

# Queries transactions data
module Results::Csv
  class Transactions < Base
    include UseStashBase

    def filename
      'transactions'
    end

    def sql_query
      <<-SQL
        SELECT
          date,
          shop_id,
          external_product_id,
          quantity,
          price,
          discount,
          order_total
        FROM orders
        WHERE created_at > '#{last_export}';
      SQL
    end
  end
end



# app/services/results/csv/base.rb

# Base serves as template for csv spreadsheets,
# It houses all common functionality between csv spreadsheets,
# creating the file, executing the datbase query, etc.
module Results::Csv
  class Base
    def initialize
      CSV.open(filepath, 'w') do |csv|
        csv << records.fields
        records.values.each { |row| csv << row }
      end
    end

    def records
      @_records ||= database.connection.execute(sql_query)
    end

    def filepath
      filename + timestamp + '.csv'
    end

    def filename
      fail 'Need to define `filename` for spreadsheet'
    end

    def sql_query
      fail 'Need to define `sql_query` for spreadsheet'
    end

    private

    def database
      ActiveRecord::Base
    end
    
    # We are using two different databases, otherwise this would be calculated in the `Csv` query
    def last_export
      @_last_export ||= Export.last.created_at
    end

    def timestamp
      Date.today.strftime('%m%d%y')
    end
  end
end



# app/services/results/csv/use_stash_base.rb

# include this to query stash database instead of default
module Results::Csv
  module UseStashBase
    def database
      StashBase
    end
  end
end

specs.rb

# spec/services/results/create_export_spec.rb

require 'rails_helper'
require_dependency 'services/results/create_export'

describe Results::CreateExport do
  describe 'results export' do
    before do
      Results::Upload.stubs(:new)
      ActionMailer::Base.deliveries = []
    end

    after :all do
      Dir.glob('*.csv').each { |f| File.delete(f) }
    end

    subject do
      Results::CreateExport.new
    end

    it 'adds row to export table' do
      subject
      expect(Export.count).to eq(1)
    end

    it 'uploads spreadsheets' do
      Results::Upload.expects(:new).times(3)
      subject
    end

    it 'sends email reminder' do
      subject
      expect(ActionMailer::Base.deliveries.count).to eq(1)
    end
  end
end



# spec/services/results/upload_spec.rb

require 'rails_helper'
require_dependency 'services/results/upload'

describe Results::Upload do
  describe '#initialize' do
    PATH = 'spec/fixtures/exported_spreadsheet.csv'

    subject do
      Results::Upload.new(PATH)
    end

    before do
      File.open(PATH, 'w')
      stub_dropbox_request
    end

    # Make sure request to dropbox api is as expected
    it 'uploads to Experimento/Shopify/export' do
      subject
    end

    it 'deletes tempfile once upload is complete' do
      subject
      expect(File.file?("exported_spreadsheet.csv")).to eq(false)
    end
  end
end


# spec/services/results/csv/assignments_spec.rb

require 'rails_helper'
require_dependency 'services/results/csv/assignments'

describe Results::Csv::Assignments do
  subject do
    Results::Csv::Assignments.new.records
  end

  context 'scope' do
    before do
      create(:assignment, :with_experiment, created_at: 10.days.ago)
      create(:export)
      create(:assignment, experiment: create(:experiment, external_product_id: 420))
    end

    it 'only queries assignments created after last export' do
      records = subject
      expect(records.count).to eq(1)
      expect(records[0]['external_product_id']).to eq('420')
    end
  end

  context 'formatting' do
    let(:assignment) { create(:assignment, :with_experiment) }

    before do
      assignment
      create :assignment, :with_experiment
    end

    it 'properly formats date_end of assignment' do
      date_end = subject[0]['date_end'].to_time.strftime('%Y-%m-%d %H:%M:%S')
      expected = (assignment.start - 1.second).strftime('%Y-%m-%d %H:%M:%S')

      expect(date_end).to eq expected
    end
  end
end



# spec/services/results/csv/transaction_spec.rb

require 'rails_helper'
require_dependency 'services/results/csv/transactions'

describe Results::Csv::Transactions do
  context 'scope' do
    before do
      create(:order, created_at: 10.seconds.ago)
      create(:export)
      create(:order)
      create(:order)
    end

    subject do
      Results::Csv::Transactions.new.records
    end

    it 'only queries transactions created after last export' do
      records = subject
      expect(records.count).to eq(2)
    end
  end
end