Make the invoice number formattable

app/models/spree/printables/invoice/base_view.rb

@@ -54,7 +54,7 @@ def shipping_methods
 
     def number
       if use_sequential_number?
-        Spree::PrintInvoice::Config.next_number
+        formatted_number
       else
         printable.number
       end
@@ -66,6 +66,18 @@ def after_save_actions
 
     private
 
+    def formatted_number
+      if (Object.const_get('::Spree::PrintInvoice::NumberFormatter') rescue false)
+        ::Spree::PrintInvoice::NumberFormatter.new(next_number).to_s
+      else
+        next_number
+      end
+    end
+
+    def next_number
+      Spree::PrintInvoice::Config.next_number
+    end
+
     def increase_invoice_number!
       Spree::PrintInvoice::Config.increase_invoice_number!
     end

spec/models/spree/printables/invoice/base_view_spec.rb

@@ -68,14 +68,17 @@
   end
 
   describe '#number' do
+    before do
+      allow(Spree::PrintInvoice::Config).to receive(:next_number) { 77 }
+    end
+
     context 'when using sequential numbers' do
       before do
         allow(Spree::PrintInvoice::Config).to receive(:use_sequential_number?) { true }
       end
 
-      it 'calls next_number on Spree::PrintInvoice::Config' do
-        expect(Spree::PrintInvoice::Config).to receive(:next_number)
-        base_view.number
+      it 'returns the next number without additional formatting' do
+        expect(base_view.number).to eq(77)
       end
     end
 
@@ -89,5 +92,23 @@
         base_view.number
       end
     end
+
+    context 'when using a NumberFormatter' do
+      before do
+        class Spree::PrintInvoice::NumberFormatter
+          def initialize(number)
+            @number = number
+          end
+
+          def to_s
+            "MY-NICE-INVOICE-#{@number}"
+          end
+        end
+      end
+
+      it 'returns a nicely formatted number' do
+        expect(base_view.number).to eq("MY-NICE-INVOICE-77")
+      end
+    end
   end
 end