18 files changed, 164 insertions, 57 deletions

diff --git a/app/assets/javascripts/notes/components/note_actions.vue b/app/assets/javascripts/notes/components/note_actions.vue
index cdbbb342331..b248aa3ae08 100644
--- a/app/assets/javascripts/notes/components/note_actions.vue
+++ b/app/assets/javascripts/notes/components/note_actions.vue
@@ -24,7 +24,7 @@ export default {
       required: true,
     },
     noteId: {
-      type: Number,
+      type: String,
       required: true,
     },
     noteUrl: {
diff --git a/app/assets/javascripts/notes/components/note_header.vue b/app/assets/javascripts/notes/components/note_header.vue
index a621418cf72..5d3f923a7b4 100644
--- a/app/assets/javascripts/notes/components/note_header.vue
+++ b/app/assets/javascripts/notes/components/note_header.vue
@@ -21,7 +21,7 @@ export default {
       default: '',
     },
     noteId: {
-      type: Number,
+      type: String,
       required: true,
     },
     includeToggle: {
diff --git a/app/controllers/concerns/issuable_actions.rb b/app/controllers/concerns/issuable_actions.rb
index 37e03d70b6f..280d0152b14 100644
--- a/app/controllers/concerns/issuable_actions.rb
+++ b/app/controllers/concerns/issuable_actions.rb
@@ -95,6 +95,9 @@ module IssuableActions
       .includes(:noteable)
       .fresh
 
+    # FIXME: import/export
+    notes = ResourceEvents::MergeIntoNotesService.new(issuable).execute(notes)
+
     notes = prepare_notes_for_rendering(notes)
     notes = notes.reject { |n| n.cross_reference_not_visible_for?(current_user) }
 
diff --git a/app/controllers/concerns/notes_actions.rb b/app/controllers/concerns/notes_actions.rb
index 5127db3f5fb..68f152cbfec 100644
--- a/app/controllers/concerns/notes_actions.rb
+++ b/app/controllers/concerns/notes_actions.rb
@@ -18,6 +18,9 @@ module NotesActions
     notes = notes_finder.execute
       .inc_relations_for_view
 
+    # FIXME: created_after
+    notes = ResourceEvents::MergeIntoNotesService.new(noteable, last_fetched_at: current_fetched_at).execute(notes)
+
     notes = prepare_notes_for_rendering(notes)
     notes = notes.reject { |n| n.cross_reference_not_visible_for?(current_user) }
 
diff --git a/app/models/resource_label_event.rb b/app/models/resource_label_event.rb
index 42c255fcd1e..48f9ecc3bbf 100644
--- a/app/models/resource_label_event.rb
+++ b/app/models/resource_label_event.rb
@@ -8,10 +8,15 @@ class ResourceLabelEvent < ActiveRecord::Base
   belongs_to :merge_request
   belongs_to :label
 
+  scope :created_after, ->(time) { where('created_at > ?', time) }
+
   validates :user, presence: true, on: :create
   validates :label, presence: true, on: :create
   validate :exactly_one_issuable
 
+  after_save :expire_etag_cache
+  after_destroy :expire_etag_cache
+
   enum action: {
     add: 1,
     remove: 2
@@ -25,6 +30,16 @@ class ResourceLabelEvent < ActiveRecord::Base
     issue || merge_request
   end
 
+  # FIXME: check again alias_method
+  def updated_at
+    created_at
+  end
+
+  # create same discussion id for all actions with the same user and time
+  def discussion_id(resource = nil)
+    Digest::SHA1.hexdigest([self.class.name, created_at, user_id].join("-"))
+  end
+
   private
 
   def exactly_one_issuable
@@ -32,4 +47,20 @@ class ResourceLabelEvent < ActiveRecord::Base
       errors.add(:base, "Exactly one of #{self.class.issuable_columns.join(', ')} is required")
     end
   end
+
+  def expire_etag_cache
+    return unless issuable&.discussions_rendered_on_frontend?
+    return unless issuable&.etag_caching_enabled?
+
+    Gitlab::EtagCaching::Store.new.touch(etag_key)
+  end
+
+  # FIXME: override for epic
+  def etag_key
+    Gitlab::Routing.url_helpers.project_noteable_notes_path(
+      project,
+      target_type: 'issue',
+      target_id: issuable.id
+    )
+  end
 end
diff --git a/app/serializers/note_entity.rb b/app/serializers/note_entity.rb
index daa5c24d0f5..07ecc335d14 100644
--- a/app/serializers/note_entity.rb
+++ b/app/serializers/note_entity.rb
@@ -4,6 +4,12 @@ class NoteEntity < API::Entities::Note
   include RequestAwareEntity
   include NotesHelper
 
+  expose :id do |note|
+    # resource events are represented as notes too, but don't
+    # have ID, discussion ID is used for them instead
+    note.id.present? ? note.id.to_s : note.discussion_id
+  end
+
   expose :type
 
   expose :author, using: NoteUserEntity
diff --git a/app/serializers/project_note_entity.rb b/app/serializers/project_note_entity.rb
index d7c4d0aacc6..ce9353ddbe4 100644
--- a/app/serializers/project_note_entity.rb
+++ b/app/serializers/project_note_entity.rb
@@ -9,7 +9,7 @@ class ProjectNoteEntity < NoteEntity
     toggle_award_emoji_project_note_path(note.project, note.id)
   end
 
-  expose :path do |note|
+  expose :path, if: -> (note, _) { note.id } do |note|
     project_note_path(note.project, note)
   end
 
diff --git a/app/services/issuable/common_system_notes_service.rb b/app/services/issuable/common_system_notes_service.rb
index 028b350ca07..ab53c38aa3a 100644
--- a/app/services/issuable/common_system_notes_service.rb
+++ b/app/services/issuable/common_system_notes_service.rb
@@ -55,7 +55,9 @@ module Issuable
       added_labels = issuable.labels - old_labels
       removed_labels = old_labels - issuable.labels
 
-      SystemNoteService.change_label(issuable, issuable.project, current_user, added_labels, removed_labels)
+      ResourceEvents::ChangeLabelsService
+        .new(issuable, current_user)
+        .execute(added_labels: added_labels, removed_labels: removed_labels)
     end
 
     def create_title_change_note(old_title)
diff --git a/app/services/labels/promote_service.rb b/app/services/labels/promote_service.rb
index 623a5f0950e..22b4b30d902 100644
--- a/app/services/labels/promote_service.rb
+++ b/app/services/labels/promote_service.rb
@@ -13,6 +13,7 @@ module Labels
 
         label_ids_for_merge(new_label).find_in_batches(batch_size: BATCH_SIZE) do |batched_ids|
           update_issuables(new_label, batched_ids)
+          update_resource_label_events(new_label, batched_ids)
           update_issue_board_lists(new_label, batched_ids)
           update_priorities(new_label, batched_ids)
           subscribe_users(new_label, batched_ids)
@@ -52,6 +53,13 @@ module Labels
         .update_all(label_id: new_label)
     end
 
+    def update_resource_label_events(new_label, label_ids)
+      # FIXME: DB - review, batch is probably not needed though (same as issuables above)
+      ResourceLabelEvent
+        .where(label: label_ids)
+        .update_all(label_id: new_label)
+    end
+
     def update_issue_board_lists(new_label, label_ids)
       List
         .where(label: label_ids)
diff --git a/app/services/resource_events/change_labels_service.rb b/app/services/resource_events/change_labels_service.rb
index 8edb0ddb3ed..950cc8d7f46 100644
--- a/app/services/resource_events/change_labels_service.rb
+++ b/app/services/resource_events/change_labels_service.rb
@@ -1,7 +1,5 @@
 # frozen_string_literal: true
 
-# This service is not used yet, it will be used for:
-# https://gitlab.com/gitlab-org/gitlab-ce/issues/48483
 module ResourceEvents
   class ChangeLabelsService
     attr_reader :resource, :user
diff --git a/app/services/resource_events/merge_into_notes_service.rb b/app/services/resource_events/merge_into_notes_service.rb
new file mode 100644
index 00000000000..fe68d591e35
--- /dev/null
+++ b/app/services/resource_events/merge_into_notes_service.rb
@@ -0,0 +1,91 @@
+# frozen_string_literal: true
+
+module ResourceEvents
+  class MergeIntoNotesService
+    FETCH_OVERLAP = 5.seconds
+
+    attr_reader :resource, :params
+
+    def initialize(resource, params = {})
+      @resource = resource
+      @params = params
+    end
+
+    def execute(notes)
+      (notes + label_notes).sort_by { |n| n.created_at }
+    end
+
+    private
+
+    def label_notes
+      label_events_by_discussion_id.map do |discussion_id, events|
+        note_from_label_events(discussion_id, events)
+      end
+    end
+
+    def note_from_label_events(discussion_id, events)
+      text = change_label_text(events)
+      issuable = events.first.issuable
+      attrs = {
+        system: true,
+        author: events.first.user,
+        created_at: events.first.created_at,
+        discussion_id: discussion_id,
+        note: text,
+        noteable: issuable,
+        system_note_metadata: SystemNoteMetadata.new(action: 'label')
+      }
+
+      if issuable.respond_to?(:project_id)
+        attrs[:project_id] = issuable.project_id
+      end
+
+      Note.new(attrs)
+    end
+
+    def label_events_by_discussion_id
+      return [] unless resource.respond_to?(:resource_label_events)
+
+      events = resource.resource_label_events.includes(:label)
+      events = since_fetch_at(events)
+
+      events.group_by { |event| event.discussion_id }
+    end
+
+    # FIXME: take from system_note, refactor
+    def change_label_text(events)
+      added_labels = events.select { |e| e.action == 'add' && e.label }.map(&:label)
+      removed_labels = events.select { |e| e.action == 'remove' && e.label }.map(&:label)
+      added_unknown_labels_count = events.select { |e| e.action == 'add' && e.label.nil? }.map(&:label).count
+      removed_unknown_labels_count = events.select { |e| e.action == 'remove' && e.label.nil? }.map(&:label).count
+      labels_count = added_labels.count + removed_labels.count + added_unknown_labels_count + removed_unknown_labels_count
+
+      references     = ->(label) { label.to_reference(format: :id) }
+      added_labels   = added_labels.map(&references).join(' ')
+      removed_labels = removed_labels.map(&references).join(' ')
+
+      text_parts = []
+
+      if added_labels.present?
+        text_parts << "added #{added_labels}"
+        text_parts << " + #{added_unknown_labels_count} deleted" if added_unknown_labels_count > 0
+        text_parts << 'and' if removed_labels.present?
+      end
+
+      if removed_labels.present?
+        text_parts << "removed #{removed_labels}"
+        text_parts << " + #{removed_unknown_labels_count} deleted" if removed_unknown_labels_count > 0
+      end
+
+      text_parts << 'label'.pluralize(labels_count)
+      text_parts.join(' ')
+    end
+
+    def since_fetch_at(events)
+      return events unless params[:last_fetched_at].present?
+
+      last_fetched_at = Time.at(params.fetch(:last_fetched_at).to_i)
+      events.created_after(last_fetched_at - FETCH_OVERLAP)
+    end
+  end
+end
diff --git a/app/services/system_note_service.rb b/app/services/system_note_service.rb
index dda89830179..3ea81445798 100644
--- a/app/services/system_note_service.rb
+++ b/app/services/system_note_service.rb
@@ -98,47 +98,6 @@ module SystemNoteService
     create_note(NoteSummary.new(issue, project, author, body, action: 'assignee'))
   end
 
-  # Called when one or more labels on a Noteable are added and/or removed
-  #
-  # noteable       - Noteable object
-  # project        - Project owning noteable
-  # author         - User performing the change
-  # added_labels   - Array of Labels added
-  # removed_labels - Array of Labels removed
-  #
-  # Example Note text:
-  #
-  #   "added ~1 and removed ~2 ~3 labels"
-  #
-  #   "added ~4 label"
-  #
-  #   "removed ~5 label"
-  #
-  # Returns the created Note object
-  def change_label(noteable, project, author, added_labels, removed_labels)
-    labels_count = added_labels.count + removed_labels.count
-
-    references     = ->(label) { label.to_reference(format: :id) }
-    added_labels   = added_labels.map(&references).join(' ')
-    removed_labels = removed_labels.map(&references).join(' ')
-
-    text_parts = []
-
-    if added_labels.present?
-      text_parts << "added #{added_labels}"
-      text_parts << 'and' if removed_labels.present?
-    end
-
-    if removed_labels.present?
-      text_parts << "removed #{removed_labels}"
-    end
-
-    text_parts << 'label'.pluralize(labels_count)
-    body = text_parts.join(' ')
-
-    create_note(NoteSummary.new(noteable, project, author, body, action: 'label'))
-  end
-
   # Called when the milestone of a Noteable is changed
   #
   # noteable  - Noteable object
diff --git a/lib/api/discussions.rb b/lib/api/discussions.rb
index 13c34e3473a..53b89f585a8 100644
--- a/lib/api/discussions.rb
+++ b/lib/api/discussions.rb
@@ -31,6 +31,8 @@ module API
             .includes(:noteable)
             .fresh
 
+          notes = ResourceEvents::MergeIntoNotesService.new(noteable).execute(notes)
+
           notes = notes.reject { |n| n.cross_reference_not_visible_for?(current_user) }
           discussions = Kaminari.paginate_array(Discussion.build_collection(notes, noteable))
 
diff --git a/lib/api/notes.rb b/lib/api/notes.rb
index 39923e6d5b5..940aa59e96d 100644
--- a/lib/api/notes.rb
+++ b/lib/api/notes.rb
@@ -37,13 +37,13 @@ module API
           # page can have less elements than :per_page even if
           # there's more than one page.
           raw_notes = noteable.notes.with_metadata.reorder(params[:order_by] => params[:sort])
-          notes =
-            # paginate() only works with a relation. This could lead to a
-            # mismatch between the pagination headers info and the actual notes
-            # array returned, but this is really a edge-case.
-            paginate(raw_notes)
-            .reject { |n| n.cross_reference_not_visible_for?(current_user) }
-          present notes, with: Entities::Note
+
+          raw_notes = ResourceEvents::MergeIntoNotesService.new(noteable).execute(raw_notes)
+          raw_notes = raw_notes.reject { |n| n.cross_reference_not_visible_for?(current_user) }
+
+          notes = Kaminari.paginate_array(raw_notes)
+
+          present paginate(notes), with: Entities::Note
         end
 
         desc "Get a single #{noteable_type.to_s.downcase} note" do
diff --git a/lib/gitlab/import_export/import_export.yml b/lib/gitlab/import_export/import_export.yml
index f69f98a78a3..9b6a3dadfad 100644
--- a/lib/gitlab/import_export/import_export.yml
+++ b/lib/gitlab/import_export/import_export.yml
@@ -19,6 +19,10 @@ project_tree:
     - milestone:
       - events:
         - :push_event_payload
+    - resource_label_events:
+      - :user
+      - label:
+          :priorities
     - :issue_assignees
   - snippets:
     - :award_emoji
diff --git a/spec/javascripts/notes/components/note_actions_spec.js b/spec/javascripts/notes/components/note_actions_spec.js
index 52cc42cb53d..55d30d69f31 100644
--- a/spec/javascripts/notes/components/note_actions_spec.js
+++ b/spec/javascripts/notes/components/note_actions_spec.js
@@ -28,7 +28,7 @@ describe('issue_note_actions component', () => {
         canEdit: true,
         canAwardEmoji: true,
         canReportAsAbuse: true,
-        noteId: 539,
+        noteId: '539',
         noteUrl: 'https://localhost:3000/group/project/merge_requests/1#note_1',
         reportAbusePath:
           '/abuse_reports/new?ref_url=http%3A%2F%2Flocalhost%3A3000%2Fgitlab-org%2Fgitlab-ce%2Fissues%2F7%23note_539&user_id=26',
diff --git a/spec/javascripts/notes/components/note_awards_list_spec.js b/spec/javascripts/notes/components/note_awards_list_spec.js
index 9d98ba219da..082f98f22f5 100644
--- a/spec/javascripts/notes/components/note_awards_list_spec.js
+++ b/spec/javascripts/notes/components/note_awards_list_spec.js
@@ -30,7 +30,7 @@ describe('note_awards_list component', () => {
       propsData: {
         awards: awardsMock,
         noteAuthorId: 2,
-        noteId: 545,
+        noteId: '545',
         canAwardEmoji: true,
         toggleAwardPath: '/gitlab-org/gitlab-ce/notes/545/toggle_award_emoji',
       },
diff --git a/spec/javascripts/notes/components/note_form_spec.js b/spec/javascripts/notes/components/note_form_spec.js
index 95d400ab3df..a938744ab46 100644
--- a/spec/javascripts/notes/components/note_form_spec.js
+++ b/spec/javascripts/notes/components/note_form_spec.js
@@ -19,7 +19,7 @@ describe('issue_note_form component', () => {
     props = {
       isEditing: false,
       noteBody: 'Magni suscipit eius consectetur enim et ex et commodi.',
-      noteId: 545,
+      noteId: '545',
     };
 
     vm = new Component({