Board list create service to create backlog list

also make available_labels in AvailableLablesService
public so that code is not duplicated

app/services/boards/lists/create_service.rb

@@ -7,34 +7,39 @@ module Boards
 
       def execute(board)
         List.transaction do
-          target = target(board)
-          position = next_position(board)
-          create_list(board, type, target, position)
+          case type
+          when :backlog
+            create_backlog(board)
+          else
+            target = target(board)
+            position = next_position(board)
+
+            create_list(board, type, target, position)
+          end
         end
       end
 
       private
 
       def type
-        :label
+        # We don't ever expect to have more than one list
+        # type param at once.
+        if params.key?('backlog')
+          :backlog
+        else
+          :label
+        end
       end
 
       def target(board)
         strong_memoize(:target) do
-          available_labels_for(board).find(params[:label_id])
+          available_labels.find(params[:label_id])
         end
       end
 
-      def available_labels_for(board)
-        options = { include_ancestor_groups: true }
-
-        if board.group_board?
-          options.merge!(group_id: parent.id, only_group_labels: true)
-        else
-          options[:project_id] = parent.id
-        end
-
-        LabelsFinder.new(current_user, options).execute
+      def available_labels
+        ::Labels::AvailableLabelsService.new(current_user, parent, {})
+          .available_labels
       end
 
       def next_position(board)
@@ -49,6 +54,12 @@ module Boards
       def create_list_attributes(type, target, position)
         { type => target, list_type: type, position: position }
       end
+
+      def create_backlog(board)
+        return board.lists.backlog.first if board.lists.backlog.exists?
+
+        board.lists.create(list_type: :backlog, position: nil)
+      end
     end
   end
 end

app/services/labels/available_labels_service.rb

@@ -39,12 +39,12 @@ module Labels
       ids.map(&:to_i) & existing_ids
     end
 
-    private
-
     def available_labels
       @available_labels ||= LabelsFinder.new(current_user, finder_params).execute
     end
 
+    private
+
     def finder_params
       params = { include_ancestor_groups: true }
 

spec/services/boards/lists/create_service_spec.rb

@@ -59,6 +59,21 @@ RSpec.describe Boards::Lists::CreateService do
           expect { service.execute(board) }.to raise_error(ActiveRecord::RecordNotFound)
         end
       end
+
+      context 'when backlog param is sent' do
+        it 'creates one and only one backlog list' do
+          service = described_class.new(parent, user, 'backlog' => true)
+          list = service.execute(board)
+
+          expect(list.list_type).to eq('backlog')
+          expect(list.position).to be_nil
+          expect(list).to be_valid
+
+          another_backlog = service.execute(board)
+
+          expect(another_backlog).to eq list
+        end
+      end
     end
 
     context 'when board parent is a project' do

spec/services/labels/available_labels_service_spec.rb

@@ -10,7 +10,7 @@ RSpec.describe Labels::AvailableLabelsService do
   let(:other_project_label) { create(:label) }
   let(:group_label) { create(:group_label, group: group) }
   let(:other_group_label) { create(:group_label) }
-  let(:labels) { [project_label, other_project_label, group_label, other_group_label] }
+  let!(:labels) { [project_label, other_project_label, group_label, other_group_label] }
 
   describe '#find_or_create_by_titles' do
     let(:label_titles) { labels.map(&:title).push('non existing title') }
@@ -89,4 +89,26 @@ RSpec.describe Labels::AvailableLabelsService do
       end
     end
   end
+
+  describe '#available_labels' do
+    context 'when parent is a project' do
+      it 'returns only relevant labels' do
+        result = described_class.new(user, project, {}).available_labels
+
+        expect(result.count).to eq(2)
+        expect(result).to include(project_label, group_label)
+        expect(result).not_to include(other_project_label, other_group_label)
+      end
+    end
+
+    context 'when parent is a group' do
+      it 'returns only relevant labels' do
+        result = described_class.new(user, group, {}).available_labels
+
+        expect(result.count).to eq(1)
+        expect(result).to include(group_label)
+        expect(result).not_to include(project_label, other_project_label, other_group_label)
+      end
+    end
+  end
 end