extract methods related to invoices from the order model to the OrderInvoiceComparator

app/controllers/spree/admin/invoices_controller.rb

@@ -19,13 +19,14 @@ module Spree
 
       def generate
         @order = Order.find_by(number: params[:order_id])
-        if @order.can_generate_new_invoice?
+        @comparator = OrderInvoiceComparator.new(@order)
+        if @comparator.can_generate_new_invoice?
           @order.invoices.create!(
             date: Time.zone.today,
             number: @order.next_invoice_number,
             data: invoice_data
           )
-        elsif @order.can_update_latest_invoice?
+        elsif @comparator.can_update_latest_invoice?
           @order.invoices.last.update!(
             date: Time.zone.today,
             data: invoice_data

app/helpers/order_helper.rb

@@ -10,7 +10,12 @@ module OrderHelper
   end
 
   def show_generate_invoice_button?(order)
-    order.can_generate_new_invoice? ||
-      order.can_update_latest_invoice?
+    comparator = order_comparator(order)
+    comparator.can_generate_new_invoice? ||
+      comparator.can_update_latest_invoice?
+  end
+
+  def order_comparator(order)
+    OrderInvoiceComparator.new(order)
   end
 end

app/models/spree/order.rb

@@ -575,39 +575,10 @@ module Spree
       end
     end
 
-    def can_generate_new_invoice?
-      return true if invoices.empty?
-
-      invoice_comparator.can_generate_new_invoice? current_state_invoice, invoices.last
-    end
-
-    def can_update_latest_invoice?
-      return false if invoices.empty?
-
-      invoice_comparator.can_update_latest_invoice? current_state_invoice, invoices.last
-    end
-
     def next_invoice_number
       invoices.count + 1
     end
 
-    def invoice_comparator
-      @invoice_comparator ||= OrderInvoiceComparator.new
-    end
-
-    def current_state_invoice
-      Invoice.new(
-        order: self,
-        data: serialize_for_invoice,
-        date: Time.zone.today,
-        number: invoices.count + 1
-      )
-    end
-
-    def serialize_for_invoice
-      Invoice::OrderSerializer.new(self).serializable_hash
-    end
-
     private
 
     def deliver_order_confirmation_email

app/services/invoice_data_generator.rb

@@ -22,6 +22,10 @@ class InvoiceDataGenerator
     new_data
   end
 
+  def serialize_for_invoice
+    Invoice::OrderSerializer.new(order).serializable_hash
+  end
+
   private
 
   def update_order_attributes
@@ -57,7 +61,7 @@ class InvoiceDataGenerator
   end
 
   def new_data
-    @new_data ||= order.serialize_for_invoice
+    @new_data ||= serialize_for_invoice
   end
 
   def old_data

app/services/order_invoice_comparator.rb

@@ -1,7 +1,15 @@
 # frozen_string_literal: true
 
 class OrderInvoiceComparator
-  def can_generate_new_invoice?(current_state_invoice, latest_invoice)
+  attr :order
+
+  def initialize(order)
+    @order = order
+  end
+
+  def can_generate_new_invoice?
+    return true if invoices.empty?
+
     # We'll use a recursive BFS algorithm to find if the invoice is outdated
     # the root will be the order
     # On each node, we'll a list of relevant attributes that will be used on the comparison
@@ -9,7 +17,9 @@ class OrderInvoiceComparator
                invoice_generation_selector)
   end
 
-  def can_update_latest_invoice?(current_state_invoice, latest_invoice)
+  def can_update_latest_invoice?
+    return false if invoices.empty?
+
     different?(current_state_invoice.presenter, latest_invoice.presenter, invoice_update_selector)
   end
 
@@ -51,4 +61,27 @@ class OrderInvoiceComparator
       end
     end
   end
+
+  private
+
+  def current_state_invoice
+    Invoice.new(
+      order: order,
+      data: serialize_for_invoice,
+      date: Time.zone.today,
+      number: invoices.count + 1
+    )
+  end
+
+  def invoices
+    order.invoices
+  end
+
+  def latest_invoice
+    invoices.last
+  end
+
+  def serialize_for_invoice
+    InvoiceDataGenerator.new(order).serialize_for_invoice
+  end
 end

spec/services/invoice_data_generator_spec.rb

@@ -5,7 +5,12 @@ require 'spec_helper'
 describe InvoiceDataGenerator do
   describe '#generate' do
     let!(:order) { create(:completed_order_with_fees) }
-    let!(:latest_invoice){ create(:invoice, order: order, data: order.serialize_for_invoice) }
+    let!(:invoice_data_generator){ InvoiceDataGenerator.new(order) }
+    let!(:latest_invoice){
+      create(:invoice,
+             order: order,
+             data: invoice_data_generator.serialize_for_invoice)
+    }
     let(:new_invoice_data) {
       InvoiceDataGenerator.new(order).generate
     }
@@ -74,7 +79,7 @@ describe InvoiceDataGenerator do
       }
 
       it "should generate a new invoice" do
-        expect(new_invoice_data).to eql order.serialize_for_invoice
+        expect(new_invoice_data).to eql InvoiceDataGenerator.new(order).serialize_for_invoice
       end
     end
   end

spec/services/order_invoice_comparator_spec.rb

@@ -5,10 +5,14 @@ require 'spec_helper'
 describe OrderInvoiceComparator do
   describe '#can_generate_new_invoice?' do
     let!(:order) { create(:completed_order_with_fees) }
-    let!(:invoice){ create(:invoice, order: order, data: order.serialize_for_invoice) }
-    let(:current_state_invoice){ order.current_state_invoice }
+    let!(:invoice_data_generator){ InvoiceDataGenerator.new(order) }
+    let!(:invoice){
+      create(:invoice,
+             order: order,
+             data: invoice_data_generator.serialize_for_invoice)
+    }
     let(:subject) {
-      OrderInvoiceComparator.new.can_generate_new_invoice?(current_state_invoice, invoice)
+      OrderInvoiceComparator.new(order).can_generate_new_invoice?
     }
 
     context "changes on the order object" do
@@ -47,10 +51,14 @@ describe OrderInvoiceComparator do
 
   describe '#can_update_latest_invoice?' do
     let!(:order) { create(:completed_order_with_fees) }
-    let!(:invoice){ create(:invoice, order: order, data: order.serialize_for_invoice) }
-    let(:current_state_invoice){ order.current_state_invoice }
+    let!(:invoice_data_generator){ InvoiceDataGenerator.new(order) }
+    let!(:invoice){
+      create(:invoice,
+             order: order,
+             data: invoice_data_generator.serialize_for_invoice)
+    }
     let(:subject) {
-      OrderInvoiceComparator.new.can_update_latest_invoice?(current_state_invoice, invoice)
+      OrderInvoiceComparator.new(order).can_update_latest_invoice?
     }
 
     context "changes on the order object" do