Refactor BulkInvoiceService to use ActiveJob

Removes use of #handle_asynchronously, which we need to do elsewhere. Fixes:
BulkInvoiceService#start_pdf_job starts a background process to create a pdf with multiple invoices
      Failure/Error:
        expect do
          service.start_pdf_job [1, 2]
        end.to enqueue_job Delayed::PerformableMethod

        expected to enqueue exactly 1 jobs, but enqueued 0
      # ./spec/services/bulk_invoice_service_spec.rb:8:in `block (3 levels) in <top (required)>'

app/jobs/bulk_invoice_job.rb

@@ -0,0 +1,25 @@
+# frozen_string_literal: true
+
+class BulkInvoiceJob < ActiveJob::Base
+  def perform(order_ids, filepath)
+    pdf = CombinePDF.new
+
+    orders_from(order_ids).each do |order|
+      invoice = renderer.render_to_string(order)
+
+      pdf << CombinePDF.parse(invoice)
+    end
+
+    pdf.save filepath
+  end
+
+  private
+
+  def orders_from(order_ids)
+    Spree::Order.where(id: order_ids).order("completed_at DESC")
+  end
+
+  def renderer
+    @renderer ||= InvoiceRenderer.new
+  end
+end

app/services/bulk_invoice_service.rb

@@ -6,17 +6,8 @@ class BulkInvoiceService
   end
 
   def start_pdf_job(order_ids)
-    pdf = CombinePDF.new
-
-    orders_from(order_ids).each do |order|
-      invoice = renderer.render_to_string(order)
-
-      pdf << CombinePDF.parse(invoice)
-    end
-
-    pdf.save "#{file_directory}/#{@id}.pdf"
+    BulkInvoiceJob.perform_later order_ids, "#{file_directory}/#{@id}.pdf"
   end
-  handle_asynchronously :start_pdf_job
 
   def invoice_created?(invoice_id)
     File.exist? filepath(invoice_id)
@@ -28,10 +19,6 @@ class BulkInvoiceService
 
   private
 
-  def orders_from(order_ids)
-    Spree::Order.where(id: order_ids).order("completed_at DESC")
-  end
-
   def new_invoice_id
     Time.zone.now.to_i.to_s
   end
@@ -40,10 +27,6 @@ class BulkInvoiceService
     'tmp/invoices'
   end
 
-  def renderer
-    @renderer ||= InvoiceRenderer.new
-  end
-
   def file_directory
     Dir.mkdir(directory) unless File.exist?(directory)
     directory

spec/services/bulk_invoice_service_spec.rb

@@ -7,9 +7,7 @@ describe BulkInvoiceService do
     it "starts a background process to create a pdf with multiple invoices" do
       expect do
         service.start_pdf_job [1, 2]
-      end.to enqueue_job Delayed::PerformableMethod
-
-      expect(Delayed::Job.last.payload_object.method_name).to eq :start_pdf_job_without_delay
+      end.to enqueue_job BulkInvoiceJob
     end
 
     it "creates a PDF invoice" do