Associate clusters model to groups

Even though we currently only should have one group for a cluster, we
allow the flexibility to associate to other groups in the future.

This also matches the runner <=> groups association.

- Adds Cluster#first_group, aliased to Cluster#group. For the
conceivable future, a cluster will have at most one group.

- Prevent mixing of group and project clusters. If project type
clusters, it should only have projects assigned.  Similarly with groups.

- Default cluster_type to :project_type. As it's very small table we can
set default and null: false in one release.

4 files changed, 92 insertions, 0 deletions

diff --git a/spec/factories/clusters/clusters.rb b/spec/factories/clusters/clusters.rb
index bbeba8ce8b9..c9f5d0a813e 100644
--- a/spec/factories/clusters/clusters.rb
+++ b/spec/factories/clusters/clusters.rb
@@ -2,13 +2,28 @@ FactoryBot.define do
   factory :cluster, class: Clusters::Cluster do
     user
     name 'test-cluster'
+    cluster_type :project_type
+
+    trait :instance do
+      cluster_type { Clusters::Cluster.cluster_types[:instance_type] }
+    end
 
     trait :project do
+      cluster_type { Clusters::Cluster.cluster_types[:project_type] }
+
       before(:create) do |cluster, evaluator|
         cluster.projects << create(:project, :repository)
       end
     end
 
+    trait :group do
+      cluster_type { Clusters::Cluster.cluster_types[:group_type] }
+
+      before(:create) do |cluster, evalutor|
+        cluster.groups << create(:group)
+      end
+    end
+
     trait :provided_by_user do
       provider_type :user
       platform_type :kubernetes
diff --git a/spec/models/clusters/cluster_spec.rb b/spec/models/clusters/cluster_spec.rb
index f5c4b0b66ae..c245e8df815 100644
--- a/spec/models/clusters/cluster_spec.rb
+++ b/spec/models/clusters/cluster_spec.rb
@@ -4,7 +4,10 @@ require 'spec_helper'
 
 describe Clusters::Cluster do
   it { is_expected.to belong_to(:user) }
+  it { is_expected.to have_many(:cluster_projects) }
   it { is_expected.to have_many(:projects) }
+  it { is_expected.to have_many(:cluster_groups) }
+  it { is_expected.to have_many(:groups) }
   it { is_expected.to have_one(:provider_gcp) }
   it { is_expected.to have_one(:platform_kubernetes) }
   it { is_expected.to have_one(:application_helm) }
@@ -178,6 +181,53 @@ describe Clusters::Cluster do
         it { expect(cluster.update(enabled: false)).to be_truthy }
       end
     end
+
+    describe 'cluster_type validations' do
+      let(:instance_cluster) { create(:cluster, :instance) }
+      let(:group_cluster) { create(:cluster, :group) }
+      let(:project_cluster) { create(:cluster, :project) }
+
+      it 'validates presence' do
+        cluster = build(:cluster, :project, cluster_type: nil)
+
+        expect(cluster).not_to be_valid
+        expect(cluster.errors.full_messages).to include("Cluster type can't be blank")
+      end
+
+      context 'project_type cluster' do
+        it 'does not allow setting group' do
+          project_cluster.groups << build(:group)
+
+          expect(project_cluster).not_to be_valid
+          expect(project_cluster.errors.full_messages).to include('Cluster cannot have groups assigned')
+        end
+      end
+
+      context 'group_type cluster' do
+        it 'does not allow setting project' do
+          group_cluster.projects << build(:project)
+
+          expect(group_cluster).not_to be_valid
+          expect(group_cluster.errors.full_messages).to include('Cluster cannot have projects assigned')
+        end
+      end
+
+      context 'instance_type cluster' do
+        it 'does not allow setting group' do
+          instance_cluster.groups << build(:group)
+
+          expect(instance_cluster).not_to be_valid
+          expect(instance_cluster.errors.full_messages).to include('Cluster cannot have groups assigned')
+        end
+
+        it 'does not allow setting project' do
+          instance_cluster.projects << build(:project)
+
+          expect(instance_cluster).not_to be_valid
+          expect(instance_cluster.errors.full_messages).to include('Cluster cannot have projects assigned')
+        end
+      end
+    end
   end
 
   describe '#provider' do
@@ -229,6 +279,23 @@ describe Clusters::Cluster do
     end
   end
 
+  describe '#group' do
+    subject { cluster.group }
+
+    context 'when cluster belongs to a group' do
+      let(:cluster) { create(:cluster, :group) }
+      let(:group) { cluster.groups.first }
+
+      it { is_expected.to eq(group) }
+    end
+
+    context 'when cluster does not belong to any group' do
+      let(:cluster) { create(:cluster) }
+
+      it { is_expected.to be_nil }
+    end
+  end
+
   describe '#applications' do
     set(:cluster) { create(:cluster) }
 
diff --git a/spec/models/clusters/group_spec.rb b/spec/models/clusters/group_spec.rb
new file mode 100644
index 00000000000..ba145342cb8
--- /dev/null
+++ b/spec/models/clusters/group_spec.rb
@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Clusters::Group do
+  it { is_expected.to belong_to(:cluster) }
+  it { is_expected.to belong_to(:group) }
+end
diff --git a/spec/models/group_spec.rb b/spec/models/group_spec.rb
index 1bf8f89e126..571b160d901 100644
--- a/spec/models/group_spec.rb
+++ b/spec/models/group_spec.rb
@@ -19,6 +19,8 @@ describe Group do
     it { is_expected.to have_one(:chat_team) }
     it { is_expected.to have_many(:custom_attributes).class_name('GroupCustomAttribute') }
     it { is_expected.to have_many(:badges).class_name('GroupBadge') }
+    it { is_expected.to have_many(:cluster_groups).class_name('Clusters::Group') }
+    it { is_expected.to have_many(:clusters).class_name('Clusters::Cluster') }
 
     describe '#members & #requesters' do
       let(:requester) { create(:user) }