Add template classes for creating Kubeconfig files

Provides a simple way to generate config files with multiple users
and/or contexts, which will be used when communicating with Kubernetes
Agents (each applicable agent will have a separate context).

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/67089

lib/gitlab/kubernetes/kubeconfig/entry/cluster.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Kubernetes
+    module Kubeconfig
+      module Entry
+        class Cluster
+          attr_reader :name
+
+          def initialize(name:, url:, ca_pem: nil)
+            @name = name
+            @url = url
+            @ca_pem = ca_pem
+          end
+
+          def to_h
+            {
+              name: name,
+              cluster: cluster
+            }
+          end
+
+          private
+
+          attr_reader :url, :ca_pem
+
+          def cluster
+            {
+              server: url,
+              'certificate-authority-data': certificate_authority_data
+            }.compact
+          end
+
+          def certificate_authority_data
+            return unless ca_pem.present?
+
+            Base64.strict_encode64(ca_pem)
+          end
+        end
+      end
+    end
+  end
+end

lib/gitlab/kubernetes/kubeconfig/entry/context.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Kubernetes
+    module Kubeconfig
+      module Entry
+        class Context
+          attr_reader :name
+
+          def initialize(name:, cluster:, user:, namespace: nil)
+            @name = name
+            @cluster = cluster
+            @user = user
+            @namespace = namespace
+          end
+
+          def to_h
+            {
+              name: name,
+              context: context
+            }
+          end
+
+          private
+
+          attr_reader :cluster, :user, :namespace
+
+          def context
+            {
+              cluster: cluster,
+              namespace: namespace,
+              user: user
+            }.compact
+          end
+        end
+      end
+    end
+  end
+end

lib/gitlab/kubernetes/kubeconfig/entry/user.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Kubernetes
+    module Kubeconfig
+      module Entry
+        class User
+          attr_reader :name
+
+          def initialize(name:, token:)
+            @name = name
+            @token = token
+          end
+
+          def to_h
+            {
+              name: name,
+              user: { token: token }
+            }
+          end
+
+          private
+
+          attr_reader :token
+        end
+      end
+    end
+  end
+end

lib/gitlab/kubernetes/kubeconfig/template.rb

+# frozen_string_literal: true
+
+module Gitlab
+  module Kubernetes
+    module Kubeconfig
+      class Template
+        ENTRIES = {
+          cluster: Gitlab::Kubernetes::Kubeconfig::Entry::Cluster,
+          user: Gitlab::Kubernetes::Kubeconfig::Entry::User,
+          context: Gitlab::Kubernetes::Kubeconfig::Entry::Context
+        }.freeze
+
+        def initialize
+          @clusters = []
+          @users = []
+          @contexts = []
+        end
+
+        def valid?
+          contexts.present?
+        end
+
+        def add_cluster(**args)
+          clusters << new_entry(:cluster, **args)
+        end
+
+        def add_user(**args)
+          users << new_entry(:user, **args)
+        end
+
+        def add_context(**args)
+          contexts << new_entry(:context, **args)
+        end
+
+        def to_h
+          {
+            apiVersion: 'v1',
+            kind: 'Config',
+            clusters: clusters.map(&:to_h),
+            users: users.map(&:to_h),
+            contexts: contexts.map(&:to_h)
+          }
+        end
+
+        def to_yaml
+          YAML.dump(to_h.deep_stringify_keys)
+        end
+
+        private
+
+        attr_reader :clusters, :users, :contexts
+
+        def new_entry(entry, **args)
+          ENTRIES.fetch(entry).new(**args)
+        end
+      end
+    end
+  end
+end

spec/lib/gitlab/kubernetes/kubeconfig/entry/cluster_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Kubernetes::Kubeconfig::Entry::Cluster do
+  describe '#to_h' do
+    let(:name) { 'name' }
+    let(:url) { 'url' }
+
+    subject { described_class.new(name: name, url: url).to_h }
+
+    it { is_expected.to eq({ name: name, cluster: { server: url } }) }
+
+    context 'with a certificate' do
+      let(:cert) { 'certificate' }
+      let(:cert_encoded) { Base64.strict_encode64(cert) }
+
+      subject { described_class.new(name: name, url: url, ca_pem: cert).to_h }
+
+      it { is_expected.to eq({ name: name, cluster: { server: url, 'certificate-authority-data': cert_encoded } }) }
+    end
+  end
+end

spec/lib/gitlab/kubernetes/kubeconfig/entry/context_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Kubernetes::Kubeconfig::Entry::Context do
+  describe '#to_h' do
+    let(:name) { 'name' }
+    let(:user) { 'user' }
+    let(:cluster) { 'cluster' }
+
+    subject { described_class.new(name: name, user: user, cluster: cluster).to_h }
+
+    it { is_expected.to eq({ name: name, context: { cluster: cluster, user: user } }) }
+
+    context 'with a namespace' do
+      let(:namespace) { 'namespace' }
+
+      subject { described_class.new(name: name, user: user, cluster: cluster, namespace: namespace).to_h }
+
+      it { is_expected.to eq({ name: name, context: { cluster: cluster, user: user, namespace: namespace } }) }
+    end
+  end
+end

spec/lib/gitlab/kubernetes/kubeconfig/entry/user_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Kubernetes::Kubeconfig::Entry::User do
+  describe '#to_h' do
+    let(:name) { 'name' }
+    let(:token) { 'token' }
+
+    subject { described_class.new(name: name, token: token).to_h }
+
+    it { is_expected.to eq({ name: name, user: { token: token } }) }
+  end
+end

spec/lib/gitlab/kubernetes/kubeconfig/template_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Kubernetes::Kubeconfig::Template do
+  let(:template) { described_class.new }
+
+  describe '#valid?' do
+    subject { template.valid? }
+
+    it { is_expected.to be_falsey }
+
+    context 'with configuration added' do
+      before do
+        template.add_context(name: 'name', cluster: 'cluster', user: 'user')
+      end
+
+      it { is_expected.to be_truthy }
+    end
+  end
+
+  describe '#to_h' do
+    subject { described_class.new.to_h }
+
+    it do
+      is_expected.to eq(
+        apiVersion: 'v1',
+        kind: 'Config',
+        clusters: [],
+        users: [],
+        contexts: []
+      )
+    end
+  end
+
+  describe '#to_yaml' do
+    subject { template.to_yaml }
+
+    it { is_expected.to eq(YAML.dump(template.to_h.deep_stringify_keys)) }
+  end
+
+  describe 'adding entries' do
+    let(:entry) { instance_double(entry_class, to_h: attributes) }
+    let(:attributes) do
+      { name: 'name', other: 'other' }
+    end
+
+    subject { template.to_h }
+
+    before do
+      expect(entry_class).to receive(:new).with(attributes).and_return(entry)
+    end
+
+    describe '#add_cluster' do
+      let(:entry_class) { Gitlab::Kubernetes::Kubeconfig::Entry::Cluster }
+
+      before do
+        template.add_cluster(**attributes)
+      end
+
+      it { is_expected.to include(clusters: [attributes]) }
+    end
+
+    describe '#add_user' do
+      let(:entry_class) { Gitlab::Kubernetes::Kubeconfig::Entry::User }
+
+      before do
+        template.add_user(**attributes)
+      end
+
+      it { is_expected.to include(users: [attributes]) }
+    end
+
+    describe '#add_context' do
+      let(:entry_class) { Gitlab::Kubernetes::Kubeconfig::Entry::Context }
+
+      before do
+        template.add_context(**attributes)
+      end
+
+      it { is_expected.to include(contexts: [attributes]) }
+    end
+  end
+end