Move NotificationService calls to Sidekiq

The NotificationService has to do quite a lot of work to calculate the
recipients for an email. Where possible, we should try to avoid doing this in an
HTTP request, because the mail are sent by Sidekiq anyway, so there's no need to
schedule those emails immediately.

This commit creates a generic Sidekiq worker that uses Global ID to serialise
and deserialise its arguments, then forwards them to the NotificationService.
The NotificationService gains an `#async` method, so you can replace:

    notification_service.new_issue(issue, current_user)

With:

    notification_service.async.new_issue(issue, current_user)

And have everything else work as normal, except that calculating the recipients
will be done by Sidekiq, which will then schedule further Sidekiq jobs to send
each email.

2 files changed, 46 insertions, 2 deletions

diff --git a/spec/workers/mail_scheduler/issue_due_worker_spec.rb b/spec/workers/mail_scheduler/issue_due_worker_spec.rb
index 48ac1b8a1a4..1026ae5b4bf 100644
--- a/spec/workers/mail_scheduler/issue_due_worker_spec.rb
+++ b/spec/workers/mail_scheduler/issue_due_worker_spec.rb
@@ -12,8 +12,8 @@ describe MailScheduler::IssueDueWorker do
       create(:issue, :opened, project: project, due_date: 2.days.from_now) # due on another day
       create(:issue, :opened, due_date: Date.tomorrow) # different project
 
-      expect_any_instance_of(NotificationService).to receive(:issue_due).with(issue1)
-      expect_any_instance_of(NotificationService).to receive(:issue_due).with(issue2)
+      expect(worker.notification_service).to receive(:issue_due).with(issue1)
+      expect(worker.notification_service).to receive(:issue_due).with(issue2)
 
       worker.perform(project.id)
     end
diff --git a/spec/workers/mail_scheduler/notification_service_worker_spec.rb b/spec/workers/mail_scheduler/notification_service_worker_spec.rb
new file mode 100644
index 00000000000..f725c8763a0
--- /dev/null
+++ b/spec/workers/mail_scheduler/notification_service_worker_spec.rb
@@ -0,0 +1,44 @@
+require 'spec_helper'
+
+describe MailScheduler::NotificationServiceWorker do
+  let(:worker) { described_class.new }
+  let(:method) { 'new_key' }
+  set(:key) { create(:personal_key) }
+
+  def serialize(*args)
+    ActiveJob::Arguments.serialize(args)
+  end
+
+  describe '#perform' do
+    it 'deserializes arguments from global IDs' do
+      expect(worker.notification_service).to receive(method).with(key)
+
+      worker.perform(method, *serialize(key))
+    end
+
+    context 'when the arguments cannot be deserialized' do
+      it 'does nothing' do
+        expect(worker.notification_service).not_to receive(method)
+
+        worker.perform(method, key.to_global_id.to_s.succ)
+      end
+    end
+
+    context 'when the method is not a public method' do
+      it 'raises NoMethodError' do
+        expect { worker.perform('notifiable?', *serialize(key)) }.to raise_error(NoMethodError)
+      end
+    end
+  end
+
+  describe '.perform_async' do
+    it 'serializes arguments as global IDs when scheduling' do
+      Sidekiq::Testing.fake! do
+        described_class.perform_async(method, key)
+
+        expect(described_class.jobs.count).to eq(1)
+        expect(described_class.jobs.first).to include('args' => [method, *serialize(key)])
+      end
+    end
+  end
+end