CSV Renderer/Helper

1_terrible.erb

<%= CSV.generate do |csv| %>
  <% csv << ["All Orders"] %>
  <% csv << [] %>
  <% total = 0.0 %>
  <% orders.each do |order| %>
    <% csv << [order.id, order.subtotal, order.tax, order.shipping, order.total] %>
    <% total += order.total %>
  <% end %>
  <% csv << [] %>
  <% csv << ["Total", total] %>
<% end %>

2_presenter.rb

class OrderCsvPresenter
  include CsvRenderer

  attr_accessor :orders
  
  def initialize(orders)
    @orders = orders
  end

  def prepare_csv
    csv_row "All Orders"
    blank_csv_row

    total = 0.0
    
    orders.each do |order|
      csv_row [order.id, order.subtotal, order.tax, order.shipping, order.total]
      total += order.total
    end
    
    blank_csv_row
    csv_row ["Total", total]
  end
end

3_renderer.rb

module CsvRenderer
  def blank_csv_row
    _csv_rows << []
  end

  def prepare_csv
    raise NotImplementedError, "Implement #prepare_csv in your class to create actual CSV rows."
  end

  def csv_row(item)
    _csv_rows << Array(item)
  end

  def to_csv
    prepare_csv
    CSV.generate do |csv|
      _csv_rows.each do |row|
        csv << row
      end
    end
  end

  private

  def _csv_rows
    @_csv_rows ||= []
  end
end

4_orders_controller.rb

class OrdersController < ApplicationController
  def index
    @orders = Order.all
    
    respond_to do |format|
      format.csv do
        data = OrderCsvPresenter.new(orders: @orders).to_csv
        send_data(data, filename: 'orders.csv', type: 'text/csv')
      end
    end
  end
end