Associate clusters model to groups34758-create-group-clusters

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.

2 files changed, 38 insertions, 0 deletions

diff --git a/app/models/clusters/cluster.rb b/app/models/clusters/cluster.rb
index 95efecfc41d..222e4217e67 100644
--- a/app/models/clusters/cluster.rb
+++ b/app/models/clusters/cluster.rb
@@ -20,6 +20,12 @@ module Clusters
     has_many :cluster_projects, class_name: 'Clusters::Project'
     has_many :projects, through: :cluster_projects, class_name: '::Project'
 
+    has_many :cluster_groups, class_name: 'Clusters::Group'
+    has_many :groups, through: :cluster_groups, class_name: '::Group'
+
+    has_one :cluster_group, -> { order(id: :desc) }, class_name: 'Clusters::Group'
+    has_one :group, through: :cluster_group, class_name: '::Group'
+
     # we force autosave to happen when we save `Cluster` model
     has_one :provider_gcp, class_name: 'Clusters::Providers::Gcp', autosave: true
 
@@ -38,8 +44,12 @@ module Clusters
     accepts_nested_attributes_for :platform_kubernetes, update_only: true
 
     validates :name, cluster_name: true
+    validates :cluster_type, presence: true
     validate :restrict_modification, on: :update
 
+    validate :no_groups, unless: :group_type?
+    validate :no_projects, unless: :project_type?
+
     delegate :status, to: :provider, allow_nil: true
     delegate :status_reason, to: :provider, allow_nil: true
     delegate :on_creation?, to: :provider, allow_nil: true
@@ -50,6 +60,12 @@ module Clusters
     delegate :available?, to: :application_ingress, prefix: true, allow_nil: true
     delegate :available?, to: :application_prometheus, prefix: true, allow_nil: true
 
+    enum cluster_type: {
+      instance_type: 1,
+      group_type: 2,
+      project_type: 3
+    }
+
     enum platform_type: {
       kubernetes: 1
     }
@@ -122,5 +138,17 @@ module Clusters
 
       true
     end
+
+    def no_groups
+      if groups.any?
+        errors.add(:cluster, 'cannot have groups assigned')
+      end
+    end
+
+    def no_projects
+      if projects.any?
+        errors.add(:cluster, 'cannot have projects assigned')
+      end
+    end
   end
 end
diff --git a/app/models/clusters/group.rb b/app/models/clusters/group.rb
new file mode 100644
index 00000000000..2b08a9e47f0
--- /dev/null
+++ b/app/models/clusters/group.rb
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+module Clusters
+  class Group < ActiveRecord::Base
+    self.table_name = 'cluster_groups'
+
+    belongs_to :cluster, class_name: 'Clusters::Cluster'
+    belongs_to :group, class_name: '::Group'
+  end
+end