Expose namespace storage statistics with GraphQL

Root namespaces have storage statistics.
This commit allows namespace owners to get those stats via GraphQL
queries like the following one

{
  namespace(fullPath: "a_namespace_path") {
    rootStorageStatistics {
      storageSize
      repositorySize
      lfsObjectsSize
      buildArtifactsSize
      packagesSize
      wikiSize
    }
  }
}

6 files changed, 31 insertions, 0 deletions

diff --git a/app/graphql/types/namespace_type.rb b/app/graphql/types/namespace_type.rb
index f105e9e6e28..35a97b5ace0 100644
--- a/app/graphql/types/namespace_type.rb
+++ b/app/graphql/types/namespace_type.rb
@@ -19,6 +19,11 @@ module Types
     field :lfs_enabled, GraphQL::BOOLEAN_TYPE, null: true, method: :lfs_enabled?
     field :request_access_enabled, GraphQL::BOOLEAN_TYPE, null: true
 
+    field :root_storage_statistics, Types::RootStorageStatisticsType,
+          null: true,
+          description: 'The aggregated storage statistics. Only available for root namespaces',
+          resolve: -> (obj, _args, _ctx) { Gitlab::Graphql::Loaders::BatchRootStorageStatisticsLoader.new(obj.id).find }
+
     field :projects,
           Types::ProjectType.connection_type,
           null: false,
diff --git a/app/graphql/types/root_storage_statistics_type.rb b/app/graphql/types/root_storage_statistics_type.rb
new file mode 100644
index 00000000000..a7498ee0a2e
--- /dev/null
+++ b/app/graphql/types/root_storage_statistics_type.rb
@@ -0,0 +1,16 @@
+# frozen_string_literal: true
+
+module Types
+  class RootStorageStatisticsType < BaseObject
+    graphql_name 'RootStorageStatistics'
+
+    authorize :read_statistics
+
+    field :storage_size, GraphQL::INT_TYPE, null: false, description: 'The total storage in bytes'
+    field :repository_size, GraphQL::INT_TYPE, null: false, description: 'The git repository size in bytes'
+    field :lfs_objects_size, GraphQL::INT_TYPE, null: false, description: 'The LFS objects size in bytes'
+    field :build_artifacts_size, GraphQL::INT_TYPE, null: false, description: 'The CI artifacts size in bytes'
+    field :packages_size, GraphQL::INT_TYPE, null: false, description: 'The packages size in bytes'
+    field :wiki_size, GraphQL::INT_TYPE, null: false, description: 'The wiki size in bytes'
+  end
+end
diff --git a/app/models/namespace/root_storage_statistics.rb b/app/models/namespace/root_storage_statistics.rb
index 56c430013ee..ae9b2f14343 100644
--- a/app/models/namespace/root_storage_statistics.rb
+++ b/app/models/namespace/root_storage_statistics.rb
@@ -8,6 +8,8 @@ class Namespace::RootStorageStatistics < ApplicationRecord
   belongs_to :namespace
   has_one :route, through: :namespace
 
+  scope :for_namespace_ids, ->(namespace_ids) { where(namespace_id: namespace_ids) }
+
   delegate :all_projects, to: :namespace
 
   def recalculate!
diff --git a/app/policies/group_policy.rb b/app/policies/group_policy.rb
index c686e7763bb..5d2b74b17a2 100644
--- a/app/policies/group_policy.rb
+++ b/app/policies/group_policy.rb
@@ -124,6 +124,8 @@ class GroupPolicy < BasePolicy
   rule { developer & developer_maintainer_access }.enable :create_projects
   rule { create_projects_disabled }.prevent :create_projects
 
+  rule { owner | admin }.enable :read_statistics
+
   def access_level
     return GroupMember::NO_ACCESS if @user.nil?
 
diff --git a/app/policies/namespace/root_storage_statistics_policy.rb b/app/policies/namespace/root_storage_statistics_policy.rb
new file mode 100644
index 00000000000..63fcaf20dfe
--- /dev/null
+++ b/app/policies/namespace/root_storage_statistics_policy.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+class Namespace::RootStorageStatisticsPolicy < BasePolicy
+  delegate { @subject.namespace }
+end
diff --git a/app/policies/namespace_policy.rb b/app/policies/namespace_policy.rb
index 2babcb0a2d9..937666c7e54 100644
--- a/app/policies/namespace_policy.rb
+++ b/app/policies/namespace_policy.rb
@@ -11,6 +11,7 @@ class NamespacePolicy < BasePolicy
     enable :create_projects
     enable :admin_namespace
     enable :read_namespace
+    enable :read_statistics
   end
 
   rule { personal_project & ~can_create_personal_project }.prevent :create_projects