implement OrderInvoiceGenerator service

app/controllers/spree/admin/invoices_controller.rb

@@ -23,20 +23,7 @@ module Spree
       def generate
         @order = Order.find_by(number: params[:order_id])
         authorize! :invoice, @order
-
-        @comparator = OrderInvoiceComparator.new(@order)
-        if @comparator.can_generate_new_invoice?
-          @order.invoices.create!(
-            date: Time.zone.today,
-            number: @order.invoices.count + 1,
-            data: invoice_data
-          )
-        elsif @comparator.can_update_latest_invoice?
-          @order.invoices.last.update!(
-            date: Time.zone.today,
-            data: invoice_data
-          )
-        end
+        OrderInvoiceGenerator.new(@order).generate_or_update_latest_invoice
         redirect_back(fallback_location: spree.admin_dashboard_path)
       end
 
@@ -56,12 +43,6 @@ module Spree
           render json: { created: false }, status: :unprocessable_entity
         end
       end
-
-      protected
-
-      def invoice_data
-        @invoice_data ||= InvoiceDataGenerator.new(@order).generate
-      end
     end
   end
 end

app/services/order_invoice_generator.rb

@@ -0,0 +1,34 @@
+# frozen_string_literal: true
+
+class OrderInvoiceGenerator
+  def initialize(order)
+    @order = order
+  end
+
+  def generate_or_update_latest_invoice
+    if comparator.can_generate_new_invoice?
+      order.invoices.create!(
+        date: Time.zone.today,
+        number: order.invoices.count + 1,
+        data: invoice_data
+      )
+    elsif comparator.can_update_latest_invoice?
+      order.invoices.last.update!(
+        date: Time.zone.today,
+        data: invoice_data
+      )
+    end
+  end
+
+  private
+
+  attr_reader :order
+
+  def comparator
+    @comparator ||= OrderInvoiceComparator.new(order)
+  end
+
+  def invoice_data
+    @invoice_data ||= InvoiceDataGenerator.new(order).generate
+  end
+end

spec/services/order_invoice_generator_spec.rb

@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe OrderInvoiceGenerator do
+  let!(:order) { create(:completed_order_with_fees) }
+  let!(:invoice_data_generator){ InvoiceDataGenerator.new(order) }
+  let!(:latest_invoice){
+    create(:invoice,
+           order:,
+           data: invoice_data_generator.serialize_for_invoice)
+  }
+
+  let(:instance) { described_class.new(order) }
+  let(:comparator){ double("OrderInvoiceComparator") }
+
+  before do
+    allow(instance).to receive(:comparator).and_return(comparator)
+  end
+
+  describe "#generate_or_update_latest_invoice" do
+    let(:subject) { instance.generate_or_update_latest_invoice }
+    context "when can generate new invoice" do
+      before do
+        expect(comparator).to receive(:can_generate_new_invoice?).and_return(true)
+      end
+
+      it "should create a new invoice" do
+        expect(instance).to receive(:invoice_data)
+        expect{ subject }.to change{ order.invoices.count }.by(1)
+        expect(order.invoices.order('created_at desc').first.number).to eq(2)
+      end
+    end
+
+    context "can update latest invoice" do
+      before do
+        allow(comparator).to receive(:can_generate_new_invoice?).and_return(false)
+        allow(comparator).to receive(:can_update_latest_invoice?).and_return(true)
+        order.update!(note: "This is an updated note")
+      end
+
+      it "should update the latest invoice" do
+        expect{ subject }.to change{ latest_invoice.reload.data }
+          .and change{ order.invoices.count }.by(0)
+      end
+    end
+
+    context "when can't generate new invoice or update latest invoice" do
+      before do
+        allow(comparator).to receive(:can_generate_new_invoice?).and_return(false)
+        allow(comparator).to receive(:can_update_latest_invoice?).and_return(false)
+      end
+
+      it "should not create or update invoices" do
+        expect(instance).not_to receive(:invoice_data)
+        expect{ subject }.to change{ order.invoices.count }.by(0)
+      end
+    end
+  end
+end