Merge branch 'fix/cycle-analytics-duration' into 'master'

fixed bug to do with calculating durations

Fixes a couple of small bugs while calculating durations in cycle analytics - probably due to some bad refactoring

- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) added
- Tests
  - [x] Added for this feature/bug
  - [ ] All builds are passing
- [x] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if it does - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/24796

See merge request !7663

app/serializers/analytics_build_entity.rb

@@ -13,7 +13,7 @@ class AnalyticsBuildEntity < Grape::Entity
   end
 
   expose :duration, as: :total_time do |build|
-    distance_of_time_as_hash(build[:duration].to_f)
+    distance_of_time_as_hash(build.duration.to_f)
   end
 
   expose :branch do

app/serializers/entity_date_helper.rb

@@ -2,7 +2,7 @@ module EntityDateHelper
   include ActionView::Helpers::DateHelper
 
   def interval_in_words(diff)
-    "#{distance_of_time_in_words(diff.to_f)} ago"
+    "#{distance_of_time_in_words(Time.now, diff)} ago"
   end
 
   # Converts seconds into a hash such as:

spec/serializers/analytics_build_entity_spec.rb

@@ -7,7 +7,7 @@ describe AnalyticsBuildEntity do
 
   context 'build with an author' do
     let(:user) { create(:user) }
-    let(:build) { create(:ci_build, author: user) }
+    let(:build) { create(:ci_build, author: user, started_at: 2.hours.ago, finished_at: 1.hour.ago) }
 
     subject { entity.as_json }
 
@@ -23,5 +23,13 @@ describe AnalyticsBuildEntity do
       expect(subject).not_to include(/token/)
       expect(subject).not_to include(/variables/)
     end
+
+    it 'contains the right started at' do
+      expect(subject[:date]).to eq('about 2 hours ago')
+    end
+
+    it 'contains the duration' do
+      expect(subject[:total_time]).to eq(hours: 1 )
+    end
   end
 end