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.

2 files changed, 40 insertions, 34 deletions

diff --git a/app/services/notification_recipient_service.rb b/app/services/notification_recipient_service.rb
index 3eb8cfcca9b..6835b14648b 100644
--- a/app/services/notification_recipient_service.rb
+++ b/app/services/notification_recipient_service.rb
@@ -11,11 +11,11 @@ module NotificationRecipientService
   end
 
   def self.build_recipients(*a)
-    Builder::Default.new(*a).recipient_users
+    Builder::Default.new(*a).notification_recipients
   end
 
   def self.build_new_note_recipients(*a)
-    Builder::NewNote.new(*a).recipient_users
+    Builder::NewNote.new(*a).notification_recipients
   end
 
   module Builder
@@ -49,25 +49,24 @@ module NotificationRecipientService
         @recipients ||= []
       end
 
-      def <<(pair)
-        users, type = pair
-
+      def add_recipients(users, type, reason)
         if users.is_a?(ActiveRecord::Relation)
           users = users.includes(:notification_settings)
         end
 
         users = Array(users)
         users.compact!
-        recipients.concat(users.map { |u| make_recipient(u, type) })
+        recipients.concat(users.map { |u| make_recipient(u, type, reason) })
       end
 
       def user_scope
         User.includes(:notification_settings)
       end
 
-      def make_recipient(user, type)
+      def make_recipient(user, type, reason)
         NotificationRecipient.new(
           user, type,
+          reason: reason,
           project: project,
           custom_action: custom_action,
           target: target,
@@ -75,14 +74,13 @@ module NotificationRecipientService
         )
       end
 
-      def recipient_users
-        @recipient_users ||=
+      def notification_recipients
+        @notification_recipients ||=
           begin
             build!
             filter!
-            users = recipients.map(&:user)
-            users.uniq!
-            users.freeze
+            recipients = self.recipients.sort_by { |r| NotificationReason.priority(r.reason) }.uniq(&:user)
+            recipients.freeze
           end
       end
 
@@ -95,13 +93,13 @@ module NotificationRecipientService
       def add_participants(user)
         return unless target.respond_to?(:participants)
 
-        self << [target.participants(user), :participating]
+        add_recipients(target.participants(user), :participating, nil)
       end
 
       def add_mentions(user, target:)
         return unless target.respond_to?(:mentioned_users)
 
-        self << [target.mentioned_users(user), :mention]
+        add_recipients(target.mentioned_users(user), :mention, NotificationReason::MENTIONED)
       end
 
       # Get project/group users with CUSTOM notification level
@@ -119,11 +117,11 @@ module NotificationRecipientService
         global_users_ids = user_ids_with_project_level_global.concat(user_ids_with_group_level_global)
         user_ids += user_ids_with_global_level_custom(global_users_ids, custom_action)
 
-        self << [user_scope.where(id: user_ids), :watch]
+        add_recipients(user_scope.where(id: user_ids), :watch, nil)
       end
 
       def add_project_watchers
-        self << [project_watchers, :watch]
+        add_recipients(project_watchers, :watch, nil)
       end
 
       # Get project users with WATCH notification level
@@ -144,7 +142,7 @@ module NotificationRecipientService
       def add_subscribed_users
         return unless target.respond_to? :subscribers
 
-        self << [target.subscribers(project), :subscription]
+        add_recipients(target.subscribers(project), :subscription, nil)
       end
 
       def user_ids_notifiable_on(resource, notification_level = nil)
@@ -195,7 +193,7 @@ module NotificationRecipientService
         return unless target.respond_to? :labels
 
         (labels || target.labels).each do |label|
-          self << [label.subscribers(project), :subscription]
+          add_recipients(label.subscribers(project), :subscription, nil)
         end
       end
     end
@@ -222,12 +220,12 @@ module NotificationRecipientService
         # Re-assign is considered as a mention of the new assignee
         case custom_action
         when :reassign_merge_request
-          self << [previous_assignee, :mention]
-          self << [target.assignee, :mention]
+          add_recipients(previous_assignee, :mention, nil)
+          add_recipients(target.assignee, :mention, NotificationReason::ASSIGNED)
         when :reassign_issue
           previous_assignees = Array(previous_assignee)
-          self << [previous_assignees, :mention]
-          self << [target.assignees, :mention]
+          add_recipients(previous_assignees, :mention, nil)
+          add_recipients(target.assignees, :mention, NotificationReason::ASSIGNED)
         end
 
         add_subscribed_users
@@ -238,6 +236,12 @@ module NotificationRecipientService
           # receive them, too.
           add_mentions(current_user, target: target)
 
+          # Add the assigned users, if any
+          assignees = custom_action == :new_issue ? target.assignees : target.assignee
+          # We use the `:participating` notification level in order to match existing legacy behavior as captured
+          # in existing specs (notification_service_spec.rb ~ line 507)
+          add_recipients(assignees, :participating, NotificationReason::ASSIGNED) if assignees
+
           add_labels_subscribers
         end
       end
diff --git a/app/services/notification_service.rb b/app/services/notification_service.rb
index be3b4b2ba07..8c84ccfcc92 100644
--- a/app/services/notification_service.rb
+++ b/app/services/notification_service.rb
@@ -85,10 +85,11 @@ class NotificationService
     recipients.each do |recipient|
       mailer.send(
         :reassigned_issue_email,
-        recipient.id,
+        recipient.user.id,
         issue.id,
         previous_assignee_ids,
-        current_user.id
+        current_user.id,
+        recipient.reason
       ).deliver_later
     end
   end
@@ -176,7 +177,7 @@ class NotificationService
       action: "resolve_all_discussions")
 
     recipients.each do |recipient|
-      mailer.resolved_all_discussions_email(recipient.id, merge_request.id, current_user.id).deliver_later
+      mailer.resolved_all_discussions_email(recipient.user.id, merge_request.id, current_user.id, recipient.reason).deliver_later
     end
   end
 
@@ -199,7 +200,7 @@ class NotificationService
 
     recipients = NotificationRecipientService.build_new_note_recipients(note)
     recipients.each do |recipient|
-      mailer.send(notify_method, recipient.id, note.id).deliver_later
+      mailer.send(notify_method, recipient.user.id, note.id).deliver_later
     end
   end
 
@@ -299,7 +300,7 @@ class NotificationService
     recipients = NotificationRecipientService.build_recipients(issue, current_user, action: 'moved')
 
     recipients.map do |recipient|
-      email = mailer.issue_moved_email(recipient, issue, new_issue, current_user)
+      email = mailer.issue_moved_email(recipient.user, issue, new_issue, current_user, recipient.reason)
       email.deliver_later
       email
     end
@@ -339,16 +340,16 @@ class NotificationService
     recipients = NotificationRecipientService.build_recipients(target, target.author, action: "new")
 
     recipients.each do |recipient|
-      mailer.send(method, recipient.id, target.id).deliver_later
+      mailer.send(method, recipient.user.id, target.id, recipient.reason).deliver_later
     end
   end
 
   def new_mentions_in_resource_email(target, new_mentioned_users, current_user, method)
     recipients = NotificationRecipientService.build_recipients(target, current_user, action: "new")
-    recipients = recipients & new_mentioned_users
+    recipients = recipients.select {|r| new_mentioned_users.include?(r.user) }
 
     recipients.each do |recipient|
-      mailer.send(method, recipient.id, target.id, current_user.id).deliver_later
+      mailer.send(method, recipient.user.id, target.id, current_user.id, recipient.reason).deliver_later
     end
   end
 
@@ -363,7 +364,7 @@ class NotificationService
     )
 
     recipients.each do |recipient|
-      mailer.send(method, recipient.id, target.id, current_user.id).deliver_later
+      mailer.send(method, recipient.user.id, target.id, current_user.id, recipient.reason).deliver_later
     end
   end
 
@@ -381,10 +382,11 @@ class NotificationService
     recipients.each do |recipient|
       mailer.send(
         method,
-        recipient.id,
+        recipient.user.id,
         target.id,
         previous_assignee_id,
-        current_user.id
+        current_user.id,
+        recipient.reason
       ).deliver_later
     end
   end
@@ -408,7 +410,7 @@ class NotificationService
     recipients = NotificationRecipientService.build_recipients(target, current_user, action: "reopen")
 
     recipients.each do |recipient|
-      mailer.send(method, recipient.id, target.id, status, current_user.id).deliver_later
+      mailer.send(method, recipient.user.id, target.id, status, current_user.id, recipient.reason).deliver_later
     end
   end