Initial work to add notification reason to emails

Adds `#build_notification_recipients` to `NotificationRecipientService`
that returns the `NotificationRecipient` objects in order to be able to
access the new attribute `reason`.

This new attribute is used in the different notifier methods in order to
add the reason as a header: `X-GitLab-NotificationReason`.

Only the reason with the most priority gets sent.

1 files changed, 19 insertions, 0 deletions

diff --git a/app/models/notification_reason.rb b/app/models/notification_reason.rb
new file mode 100644
index 00000000000..c3965565022
--- /dev/null
+++ b/app/models/notification_reason.rb
@@ -0,0 +1,19 @@
+# Holds reasons for a notification to have been sent as well as a priority list to select which reason to use
+# above the rest
+class NotificationReason
+  OWN_ACTIVITY = 'own_activity'.freeze
+  ASSIGNED = 'assigned'.freeze
+  MENTIONED = 'mentioned'.freeze
+
+  # Priority list for selecting which reason to return in the notification
+  REASON_PRIORITY = [
+    OWN_ACTIVITY,
+    ASSIGNED,
+    MENTIONED
+  ].freeze
+
+  # returns the priority of a reason as an integer
+  def self.priority(reason)
+    REASON_PRIORITY.index(reason) || REASON_PRIORITY.length + 1
+  end
+end