[api] Introduce scope for assigned and unassigned reviews

Use case of this is when e.g. maintenance group assigns a review to a user, the new review should not be displayed
in maintenance statistics. Only the original one is of interested for them.

src/api/app/models/review.rb

@@ -18,6 +18,15 @@ class NotFoundError < APIException
 
   validate :check_initial, on: [:create]
 
+  HISTORY_ELEMENTS_ASSIGNED_SUB_QUERY = <<-SQL
+    SELECT COUNT(history_elements.id) FROM history_elements
+    WHERE history_elements.op_object_id = reviews.id
+    AND history_elements.type = 'HistoryElement::ReviewAssigned'
+  SQL
+
+  scope :assigned, -> { where("(#{HISTORY_ELEMENTS_ASSIGNED_SUB_QUERY}) > 0") }
+  scope :unassigned, -> { where("(#{HISTORY_ELEMENTS_ASSIGNED_SUB_QUERY}) = 0") }
+
   before_validation(on: :create) do
     if read_attribute(:state).nil?
       self.state = :new

src/api/spec/factories/history_elements.rb

@@ -0,0 +1,9 @@
+FactoryGirl.define do
+  factory :history_element_review_assigned, class: 'HistoryElement::ReviewAssigned' do
+    type { 'HistoryElement::ReviewAssigned' }
+  end
+
+  factory :history_element_review_accepted, class: 'HistoryElement::ReviewAccepted' do
+    type { 'HistoryElement::ReviewAccepted' }
+  end
+end

src/api/spec/factories/review.rb

@@ -0,0 +1,9 @@
+FactoryGirl.define do
+  factory :review do
+    state :new
+
+    factory :user_review do
+      by_user { create(:user) }
+    end
+  end
+end

src/api/spec/models/review_spec.rb

@@ -1,5 +1,41 @@
 require 'rails_helper'
 
+RSpec.shared_context 'some assigned reviews and some unassigned reviews' do
+  let!(:user) { create(:user) }
+
+  let!(:review_assigned1) { create(:review, by_user: user.login) }
+  let!(:review_assigned2) { create(:review, by_user: user.login) }
+  let!(:review_unassigned1) { create(:review, by_user: user.login) }
+  let!(:review_unassigned2) { create(:review, by_user: user.login) }
+
+  let!(:history_element1) do
+    create(:history_element_review_assigned, op_object_id: review_assigned1.id, user_id: user.id)
+  end
+  let!(:history_element2) do
+    create(:history_element_review_assigned, op_object_id: review_assigned2.id, user_id: user.id)
+  end
+  let!(:history_element3) do
+    create(:history_element_review_accepted, op_object_id: review_assigned2.id, user_id: user.id)
+  end
+  let!(:history_element4) do
+    create(:history_element_review_accepted, op_object_id: review_unassigned1.id, user_id: user.id)
+  end
+end
+
 RSpec.describe Review do
   it { should belong_to(:bs_request).touch(true) }
-end
+
+  describe '.assigned' do
+    include_context 'some assigned reviews and some unassigned reviews'
+
+    subject { Review.assigned }
+    it { is_expected.to match_array([review_assigned1, review_assigned2]) }
+  end
+
+  describe '.unassigned' do
+    include_context 'some assigned reviews and some unassigned reviews'
+
+    subject { Review.unassigned }
+    it { is_expected.to match_array([review_unassigned1, review_unassigned2]) }
+  end
+end