Backup subject's name in case subject is removed

Fixes a bug where notifications look like the following if the subject
vm has been removed:

'Virtual Machine %{subject} has been provisioned.'

https://bugzilla.redhat.com/show_bug.cgi?id=1469372

app/models/notification.rb

@@ -13,6 +13,8 @@ class Notification < ApplicationRecord
   # Do not emit notifications if they are not enabled for the server
   after_commit :emit_message, :on => :create
 
+  before_save :backup_subject_name
+
   serialize :options, Hash
   default_value_for(:options) { Hash.new }
 
@@ -40,6 +42,12 @@ def to_h
     }
   end
 
+  def backup_subject_name
+    return unless subject
+    backup_name = (subject.try(:name) || subject.try(:description))
+    self.options[:subject] = backup_name if backup_name
+  end
+
   def seen_by_all_recipients?
     notification_recipients.unseen.empty?
   end

spec/models/notification_spec.rb

@@ -112,6 +112,44 @@
                                        )
       )
     end
+
+    context "subject text" do
+      let(:vm) { FactoryGirl.create(:vm, :tenant => tenant) }
+      subject { Notification.create(:type => :vm_snapshot_failure, :subject => vm, :options => {:error => "oops", :snapshot_op => "create"}) }
+
+      it "stuffs subject into options hash in case the subject is destroyed" do
+        expect(subject.options[:subject]).to eql(subject.subject.name)
+      end
+
+      it "detects a rename of the subject" do
+        subject
+        vm_name = "#{vm.name}_1"
+        vm.update(:name => vm_name)
+
+        note = Notification.first
+        expect(note.to_h.fetch_path(:bindings, :subject, :text)).to eql(vm_name)
+      end
+
+      it "retains name incase subject is destroyed" do
+        subject
+        vm_name = vm.name
+        vm.destroy
+
+        note = Notification.first
+        expect(note.to_h.fetch_path(:bindings, :subject, :text)).to eql(vm_name)
+      end
+
+      it "doesn't detect subject rename if subject is destroyed" do
+        subject
+        original_name = vm.name
+        vm_name = "#{vm.name}_1"
+        vm.update(:name => vm_name)
+        vm.destroy
+
+        note = Notification.first
+        expect(note.to_h.fetch_path(:bindings, :subject, :text)).to eql(original_name)
+      end
+    end
   end
 
   describe "#seen_by_all_recipients?" do