Add event presenter

This presenter will be used in an upcoming MR which adds
rendering of epic events on group activity page.

app/helpers/events_helper.rb

@@ -103,7 +103,7 @@ module EventsHelper
       words << "at"
     end
 
-    words << event.project_name
+    words << event.resource_parent_name
 
     words.join(" ")
   end
@@ -223,3 +223,5 @@ module EventsHelper
     end
   end
 end
+
+EventsHelper.prepend_if_ee('EE::EventsHelper')

app/models/event.rb

@@ -3,6 +3,8 @@
 class Event < ApplicationRecord
   include Sortable
   include FromUnion
+  include Presentable
+
   default_scope { reorder(nil) }
 
   CREATED   = 1
@@ -135,6 +137,10 @@ class Event < ApplicationRecord
     end
   end
 
+  def present
+    super(presenter_class: ::EventPresenter)
+  end
+
   # rubocop:disable Metrics/CyclomaticComplexity
   # rubocop:disable Metrics/PerceivedComplexity
   def visible_to_user?(user = nil)
@@ -161,12 +167,8 @@ class Event < ApplicationRecord
   # rubocop:enable Metrics/PerceivedComplexity
   # rubocop:enable Metrics/CyclomaticComplexity
 
-  def project_name
-    if project
-      project.full_name
-    else
-      "(deleted project)"
-    end
+  def resource_parent
+    project || group
   end
 
   def target_title

app/presenters/event_presenter.rb

+# frozen_string_literal: true
+
+class EventPresenter < Gitlab::View::Presenter::Delegated
+  presents :event
+
+  def resource_parent_name
+    resource_parent&.full_name || ''
+  end
+
+  def target_link_options
+    case resource_parent
+    when Group
+      [event.group, event.target]
+    when Project
+      [event.project.namespace.becomes(Namespace), event.project, event.target]
+    else
+      ''
+    end
+  end
+end

app/views/events/_event.atom.builder

 return unless event.visible_to_user?(current_user)
 
+event = event.present
+
 xml.entry do
   xml.id      "tag:#{request.host},#{event.created_at.strftime("%Y-%m-%d")}:#{event.id}"
   xml.link    href: event_feed_url(event)

app/views/events/_event.html.haml

+- event = event.present
+
 - if event.visible_to_user?(current_user)
   .event-item
     .event-item-timestamp

app/views/events/_event_scope.html.haml

@@ -2,6 +2,5 @@
   = event_preposition(event)
   - if event.project
     = link_to_project(event.project)
-  - else
-    = event.project_name
-
+  - elsif event.group
+    = link_to event.resource_parent_name, group_path(event.group)

app/views/events/event/_common.html.haml

@@ -8,7 +8,7 @@
     %span.event-type.d-inline-block.append-right-4{ class: event.action_name }
       = event.action_name
     %span.event-target-type.append-right-4= event.target_type.titleize.downcase
-    = link_to [event.project.namespace.becomes(Namespace), event.project, event.target], class: 'has-tooltip event-target-link append-right-4', title: event.target_title do
+    = link_to event.target_link_options, class: 'has-tooltip event-target-link append-right-4', title: event.target_title do
       = event.target.reference_link_text
     - unless event.milestone?
       %span.event-target-title.append-right-4{ dir: "auto" }
@@ -17,4 +17,4 @@
     %span.event-type.d-inline-block.append-right-4{ class: event.action_name }
       = event_action_name(event)
 
-  = render "events/event_scope", event: event
+  = render "events/event_scope", event: event if event.resource_parent.present?

app/views/events/event/_created_project.html.haml

@@ -10,4 +10,4 @@
   - if event.project
     = link_to_project(event.project)
   - else
-    = event.project_name
+    = event.resource_parent_name

app/views/users/calendar_activities.html.haml

@@ -27,7 +27,7 @@
             - if event.project
               = link_to_project(event.project)
             - else
-              = event.project_name
+              = event.resource_parent_name
         - else
           made a private contribution
 - else

spec/helpers/events_helper_spec.rb

@@ -27,7 +27,7 @@ describe EventsHelper do
   end
 
   describe '#event_feed_url' do
-    let(:event) { create(:event) }
+    let(:event) { create(:event).present }
     let(:project) { create(:project, :public, :repository) }
 
     context 'issue' do

spec/presenters/event_presenter_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe EventPresenter do
+  include Gitlab::Routing.url_helpers
+
+  set(:group) { create(:group) }
+  set(:project) { create(:project, group: group) }
+  set(:target) { create(:milestone, project: project) }
+  set(:group_event) { create(:event, :created, project: nil, group: group, target: target) }
+  set(:project_event) { create(:event, :created, project: project, target: target) }
+
+  describe '#resource_parent_name' do
+    context 'with group event' do
+      subject { group_event.present.resource_parent_name }
+
+      it { is_expected.to eq(group.full_name) }
+    end
+
+    context 'with project label' do
+      subject { project_event.present.resource_parent_name }
+
+      it { is_expected.to eq(project.full_name) }
+    end
+  end
+
+  describe '#target_link_options' do
+    context 'with group event' do
+      subject { group_event.present.target_link_options }
+
+      it { is_expected.to eq([group, target]) }
+    end
+
+    context 'with project label' do
+      subject { project_event.present.target_link_options }
+
+      it { is_expected.to eq([group.becomes(Namespace), project, target]) }
+    end
+  end
+end