Add service to create project labels

app/services/labels/create_service.rb

+module Labels
+  class CreateService
+    def initialize(current_user, project, params = {})
+      @current_user = current_user
+      @group = project.group
+      @project = project
+      @params = params.dup
+    end
+
+    def execute
+      find_or_create_label
+    end
+
+    private
+
+    attr_reader :current_user, :group, :project, :params
+
+    def available_labels
+      @available_labels ||= LabelsFinder.new(current_user, project_id: project.id).execute
+    end
+
+    def find_or_create_label
+      new_label = available_labels.find_by(title: title)
+      new_label ||= project.labels.create(params)
+
+      new_label
+    end
+
+    def title
+      params[:title] || params[:name]
+    end
+  end
+end

spec/services/labels/create_service_spec.rb

+require 'spec_helper'
+
+describe Labels::CreateService, services: true do
+  describe '#execute' do
+    let(:user)    { create(:user) }
+    let(:group)   { create(:group) }
+    let(:project) { create(:project, namespace: group) }
+
+    let(:params) do
+      {
+        title: 'Security',
+        description: 'Security related stuff.',
+        color: '#FF0000'
+      }
+    end
+
+    subject(:service) { described_class.new(user, project, params) }
+
+    before do
+      project.team << [user, :developer]
+    end
+
+    context 'when label does not exist at group level' do
+      it 'creates a new label at project level' do
+        expect { service.execute }.to change(project.labels, :count).by(1)
+      end
+    end
+
+    context 'when label exists at group level' do
+      it 'returns the group label' do
+        group_label = create(:group_label, group: group, title: 'Security')
+
+        expect(service.execute).to eq group_label
+      end
+    end
+
+    context 'when label does not exist at group level' do
+      it 'creates a new label at project leve' do
+        expect { service.execute }.to change(project.labels, :count).by(1)
+      end
+    end
+
+    context 'when label exists at project level' do
+      it 'returns the project label' do
+        project_label = create(:label, project: project, title: 'Security')
+
+        expect(service.execute).to eq project_label
+      end
+    end
+  end
+end