Implement method that updates a stage status

app/models/ci/stage.rb

@@ -3,6 +3,7 @@ module Ci
     extend Ci::Model
     include Importable
     include HasStatus
+    include Gitlab::OptimisticLocking
 
     enumerate_status!
 
@@ -15,5 +16,51 @@ module Ci
     validates :project, presence: true, unless: :importing?
     validates :pipeline, presence: true, unless: :importing?
     validates :name, presence: true, unless: :importing?
+
+    state_machine :status, initial: :created do
+      event :enqueue do
+        transition created: :pending
+        transition [:success, :failed, :canceled, :skipped] => :running
+      end
+
+      event :run do
+        transition any - [:running] => :running
+      end
+
+      event :skip do
+        transition any - [:skipped] => :skipped
+      end
+
+      event :drop do
+        transition any - [:failed] => :failed
+      end
+
+      event :succeed do
+        transition any - [:success] => :success
+      end
+
+      event :cancel do
+        transition any - [:canceled] => :canceled
+      end
+
+      event :block do
+        transition any - [:manual] => :manual
+      end
+    end
+
+    def update!
+      retry_optimistic_lock(self) do
+        case commit_statuses.latest.status
+        when 'pending' then enqueue
+        when 'running' then run
+        when 'success' then succeed
+        when 'failed' then drop
+        when 'canceled' then cancel
+        when 'manual' then block
+        when 'skipped' then skip
+        else skip
+        end
+      end
+    end
   end
 end

spec/models/ci/stage_spec.rb

 require 'spec_helper'
 
 describe Ci::Stage, :models do
-  describe 'associations' do
   let(:stage) { create(:ci_stage_entity) }
 
+  describe 'associations' do
     before do
       create(:ci_build, stage_id: stage.id)
       create(:commit_status, stage_id: stage.id)
@@ -39,4 +39,22 @@ describe Ci::Stage, :models do
       end
     end
   end
+
+  describe 'update!' do
+    context 'when stage objects needs to be updated' do
+      before do
+        create(:ci_build, :success, stage_id: stage.id)
+        create(:ci_build, :running, stage_id: stage.id)
+      end
+
+      it 'updates stage status correctly' do
+        expect { stage.update! }
+          .to change { stage.reload.status }
+          .to 'running'
+      end
+    end
+
+    context 'when stage object is locked' do
+    end
+  end
 end