Use processed_at for notification delivery

A notification is considered processed if we’ve initiated delivery. This
is different than saying the delivery has completed; we may have skipped
delivery or the email job may have failed. This is cheating a bit; it
might be better to put "processed_at" after the actual email delivery
but I’d probably end up building another wrapper job around individual
email sends. I’m skipping that complexity for now.

I should also consider adding an index for the notification query.

Author: rossta

app/jobs/notifications/event_job.rb

@@ -4,7 +4,10 @@ class Notifications::EventJob < ApplicationJob
   def perform(event)
     # Enqueue individual deliveries
     event.notifications.each do |notification|
-      event.deliver_notification(notification)
+      notification.transaction do
+        event.deliver_notification(notification)
+        notification.touch(:processed_at)
+      end
     end
   end
 end

app/models/notification.rb

@@ -5,4 +5,6 @@ class Notification < ApplicationRecord
   scope :newest_first, -> { order(created_at: :desc) }
 
   delegate :params, :record, to: :event
+
+  scope :processed, -> { where.not(processed_at: nil) }
 end

app/notifiers/welcome_notifier.rb

@@ -16,6 +16,6 @@ def deliver_notification(notification)
   end
 
   def deliver_to?(recipient)
-    Notification.joins(:notification_event).where(recipient: recipient, notification_event: {type: self.class.name}).count < 2
+    Notification.processed.joins(:notification_event).where(recipient: recipient, notification_event: {type: self.class.name}).count < 1
   end
 end