refactor(kubernetes): move provider initialization into factory (#365)

Signed-off-by: Calum Murray <cmurray@redhat.com>

pkg/kubernetes/provider.go

@@ -2,7 +2,6 @@ package kubernetes
 
 import (
 	"context"
-	"fmt"
 
 	"github.com/containers/kubernetes-mcp-server/pkg/config"
 	"k8s.io/client-go/discovery/cached/memory"
@@ -12,10 +11,6 @@ import (
 	"k8s.io/client-go/tools/clientcmd"
 )
 
-const (
-	KubeConfigTargetParameterName = "context"
-)
-
 type ManagerProvider interface {
 	GetTargets(ctx context.Context) ([]string, error)
 	GetManagerFor(ctx context.Context, target string) (*Manager, error)
@@ -25,20 +20,6 @@ type ManagerProvider interface {
 	Close()
 }
 
-type kubeConfigClusterProvider struct {
-	defaultContext string
-	managers       map[string]*Manager
-}
-
-var _ ManagerProvider = &kubeConfigClusterProvider{}
-
-type singleClusterProvider struct {
-	strategy string
-	manager  *Manager
-}
-
-var _ ManagerProvider = &singleClusterProvider{}
-
 func NewManagerProvider(cfg *config.StaticConfig) (ManagerProvider, error) {
 	m, err := NewManager(cfg)
 	if err != nil {
@@ -46,137 +27,13 @@ func NewManagerProvider(cfg *config.StaticConfig) (ManagerProvider, error) {
 	}
 
 	strategy := resolveStrategy(cfg, m)
-	switch strategy {
-	case config.ClusterProviderKubeConfig:
-		return newKubeConfigClusterProvider(m)
-	case config.ClusterProviderInCluster, config.ClusterProviderDisabled:
-		return newSingleClusterProvider(m, strategy)
-	default:
-		return nil, fmt.Errorf(
-			"invalid ClusterProviderStrategy '%s', must be 'kubeconfig', 'in-cluster', or 'disabled'",
-			strategy,
-		)
-	}
-}
 
-func newKubeConfigClusterProvider(m *Manager) (*kubeConfigClusterProvider, error) {
+	factory, err := getProviderFactory(strategy)
-	// Handle in-cluster mode
-	if m.IsInCluster() {
-		return nil, fmt.Errorf("kubeconfig ClusterProviderStrategy is invalid for in-cluster deployments")
-	}
-
-	rawConfig, err := m.clientCmdConfig.RawConfig()
 	if err != nil {
 		return nil, err
 	}
 
-	allClusterManagers := map[string]*Manager{
+	return factory(m, cfg)
-		rawConfig.CurrentContext: m, // we already initialized a manager for the default context, let's use it
-	}
-
-	for name := range rawConfig.Contexts {
-		if name == rawConfig.CurrentContext {
-			continue // already initialized this, don't want to set it to nil
-		}
-
-		allClusterManagers[name] = nil
-	}
-
-	return &kubeConfigClusterProvider{
-		defaultContext: rawConfig.CurrentContext,
-		managers:       allClusterManagers,
-	}, nil
-}
-
-func newSingleClusterProvider(m *Manager, strategy string) (*singleClusterProvider, error) {
-	if strategy == config.ClusterProviderInCluster && !m.IsInCluster() {
-		return nil, fmt.Errorf("server must be deployed in cluster for the in-cluster ClusterProviderStrategy")
-	}
-
-	return &singleClusterProvider{
-		manager:  m,
-		strategy: strategy,
-	}, nil
-}
-
-func (k *kubeConfigClusterProvider) GetTargets(ctx context.Context) ([]string, error) {
-	contextNames := make([]string, 0, len(k.managers))
-	for cluster := range k.managers {
-		contextNames = append(contextNames, cluster)
-	}
-
-	return contextNames, nil
-}
-
-func (k *kubeConfigClusterProvider) GetTargetParameterName() string {
-	return KubeConfigTargetParameterName
-}
-
-func (k *kubeConfigClusterProvider) GetManagerFor(ctx context.Context, context string) (*Manager, error) {
-	m, ok := k.managers[context]
-	if ok && m != nil {
-		return m, nil
-	}
-
-	baseManager := k.managers[k.defaultContext]
-
-	if baseManager.IsInCluster() {
-		// In cluster mode, so context switching is not applicable
-		return baseManager, nil
-	}
-
-	m, err := baseManager.newForContext(context)
-	if err != nil {
-		return nil, err
-	}
-
-	k.managers[context] = m
-
-	return m, nil
-}
-
-func (k *kubeConfigClusterProvider) GetDefaultTarget() string {
-	return k.defaultContext
-}
-
-func (k *kubeConfigClusterProvider) WatchTargets(onKubeConfigChanged func() error) {
-	m := k.managers[k.defaultContext]
-
-	m.WatchKubeConfig(onKubeConfigChanged)
-}
-
-func (k *kubeConfigClusterProvider) Close() {
-	m := k.managers[k.defaultContext]
-
-	m.Close()
-}
-
-func (s *singleClusterProvider) GetTargets(ctx context.Context) ([]string, error) {
-	return []string{""}, nil
-}
-
-func (s *singleClusterProvider) GetManagerFor(ctx context.Context, target string) (*Manager, error) {
-	if target != "" {
-		return nil, fmt.Errorf("unable to get manager for other context/cluster with %s strategy", s.strategy)
-	}
-
-	return s.manager, nil
-}
-
-func (s *singleClusterProvider) GetDefaultTarget() string {
-	return ""
-}
-
-func (s *singleClusterProvider) GetTargetParameterName() string {
-	return ""
-}
-
-func (s *singleClusterProvider) WatchTargets(watch func() error) {
-	s.manager.WatchKubeConfig(watch)
-}
-
-func (s *singleClusterProvider) Close() {
-	s.manager.Close()
 }
 
 func (m *Manager) newForContext(context string) (*Manager, error) {

pkg/kubernetes/provider_kubeconfig.go

@@ -0,0 +1,109 @@
+package kubernetes
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/containers/kubernetes-mcp-server/pkg/config"
+)
+
+// KubeConfigTargetParameterName is the parameter name used to specify
+// the kubeconfig context when using the kubeconfig cluster provider strategy.
+const KubeConfigTargetParameterName = "context"
+
+// kubeConfigClusterProvider implements ManagerProvider for managing multiple
+// Kubernetes clusters using different contexts from a kubeconfig file.
+// It lazily initializes managers for each context as they are requested.
+type kubeConfigClusterProvider struct {
+	defaultContext string
+	managers       map[string]*Manager
+}
+
+var _ ManagerProvider = &kubeConfigClusterProvider{}
+
+func init() {
+	RegisterProvider(config.ClusterProviderKubeConfig, newKubeConfigClusterProvider)
+}
+
+// newKubeConfigClusterProvider creates a provider that manages multiple clusters
+// via kubeconfig contexts. Returns an error if the manager is in-cluster mode.
+func newKubeConfigClusterProvider(m *Manager, cfg *config.StaticConfig) (ManagerProvider, error) {
+	// Handle in-cluster mode
+	if m.IsInCluster() {
+		return nil, fmt.Errorf("kubeconfig ClusterProviderStrategy is invalid for in-cluster deployments")
+	}
+
+	rawConfig, err := m.clientCmdConfig.RawConfig()
+	if err != nil {
+		return nil, err
+	}
+
+	allClusterManagers := map[string]*Manager{
+		rawConfig.CurrentContext: m, // we already initialized a manager for the default context, let's use it
+	}
+
+	for name := range rawConfig.Contexts {
+		if name == rawConfig.CurrentContext {
+			continue // already initialized this, don't want to set it to nil
+		}
+
+		allClusterManagers[name] = nil
+	}
+
+	return &kubeConfigClusterProvider{
+		defaultContext: rawConfig.CurrentContext,
+		managers:       allClusterManagers,
+	}, nil
+}
+
+func (k *kubeConfigClusterProvider) GetTargets(ctx context.Context) ([]string, error) {
+	contextNames := make([]string, 0, len(k.managers))
+	for cluster := range k.managers {
+		contextNames = append(contextNames, cluster)
+	}
+
+	return contextNames, nil
+}
+
+func (k *kubeConfigClusterProvider) GetTargetParameterName() string {
+	return KubeConfigTargetParameterName
+}
+
+func (k *kubeConfigClusterProvider) GetManagerFor(ctx context.Context, context string) (*Manager, error) {
+	m, ok := k.managers[context]
+	if ok && m != nil {
+		return m, nil
+	}
+
+	baseManager := k.managers[k.defaultContext]
+
+	if baseManager.IsInCluster() {
+		// In cluster mode, so context switching is not applicable
+		return baseManager, nil
+	}
+
+	m, err := baseManager.newForContext(context)
+	if err != nil {
+		return nil, err
+	}
+
+	k.managers[context] = m
+
+	return m, nil
+}
+
+func (k *kubeConfigClusterProvider) GetDefaultTarget() string {
+	return k.defaultContext
+}
+
+func (k *kubeConfigClusterProvider) WatchTargets(onKubeConfigChanged func() error) {
+	m := k.managers[k.defaultContext]
+
+	m.WatchKubeConfig(onKubeConfigChanged)
+}
+
+func (k *kubeConfigClusterProvider) Close() {
+	m := k.managers[k.defaultContext]
+
+	m.Close()
+}

pkg/kubernetes/provider_registry.go

@@ -0,0 +1,47 @@
+package kubernetes
+
+import (
+	"fmt"
+	"sort"
+
+	"github.com/containers/kubernetes-mcp-server/pkg/config"
+)
+
+// ProviderFactory creates a new ManagerProvider instance for a given strategy.
+// Implementations should validate that the Manager is compatible with their strategy
+// (e.g., kubeconfig provider should reject in-cluster managers).
+type ProviderFactory func(m *Manager, cfg *config.StaticConfig) (ManagerProvider, error)
+
+var providerFactories = make(map[string]ProviderFactory)
+
+// RegisterProvider registers a provider factory for a given strategy name.
+// This should be called from init() functions in provider implementation files.
+// Panics if a provider is already registered for the given strategy.
+func RegisterProvider(strategy string, factory ProviderFactory) {
+	if _, exists := providerFactories[strategy]; exists {
+		panic(fmt.Sprintf("provider already registered for strategy '%s'", strategy))
+	}
+	providerFactories[strategy] = factory
+}
+
+// getProviderFactory retrieves a registered provider factory by strategy name.
+// Returns an error if no provider is registered for the given strategy.
+func getProviderFactory(strategy string) (ProviderFactory, error) {
+	factory, ok := providerFactories[strategy]
+	if !ok {
+		available := GetRegisteredStrategies()
+		return nil, fmt.Errorf("no provider registered for strategy '%s', available strategies: %v", strategy, available)
+	}
+	return factory, nil
+}
+
+// GetRegisteredStrategies returns a sorted list of all registered strategy names.
+// This is useful for error messages and debugging.
+func GetRegisteredStrategies() []string {
+	strategies := make([]string, 0, len(providerFactories))
+	for strategy := range providerFactories {
+		strategies = append(strategies, strategy)
+	}
+	sort.Strings(strategies)
+	return strategies
+}

pkg/kubernetes/provider_single.go

@@ -0,0 +1,66 @@
+package kubernetes
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/containers/kubernetes-mcp-server/pkg/config"
+)
+
+// singleClusterProvider implements ManagerProvider for managing a single
+// Kubernetes cluster. Used for in-cluster deployments or when multi-cluster
+// support is disabled.
+type singleClusterProvider struct {
+	strategy string
+	manager  *Manager
+}
+
+var _ ManagerProvider = &singleClusterProvider{}
+
+func init() {
+	RegisterProvider(config.ClusterProviderInCluster, newSingleClusterProvider(config.ClusterProviderInCluster))
+	RegisterProvider(config.ClusterProviderDisabled, newSingleClusterProvider(config.ClusterProviderDisabled))
+}
+
+// newSingleClusterProvider creates a provider that manages a single cluster.
+// Validates that the manager is in-cluster when the in-cluster strategy is used.
+func newSingleClusterProvider(strategy string) ProviderFactory {
+	return func(m *Manager, cfg *config.StaticConfig) (ManagerProvider, error) {
+		if strategy == config.ClusterProviderInCluster && !m.IsInCluster() {
+			return nil, fmt.Errorf("server must be deployed in cluster for the in-cluster ClusterProviderStrategy")
+		}
+
+		return &singleClusterProvider{
+			manager:  m,
+			strategy: strategy,
+		}, nil
+	}
+}
+
+func (s *singleClusterProvider) GetTargets(ctx context.Context) ([]string, error) {
+	return []string{""}, nil
+}
+
+func (s *singleClusterProvider) GetManagerFor(ctx context.Context, target string) (*Manager, error) {
+	if target != "" {
+		return nil, fmt.Errorf("unable to get manager for other context/cluster with %s strategy", s.strategy)
+	}
+
+	return s.manager, nil
+}
+
+func (s *singleClusterProvider) GetDefaultTarget() string {
+	return ""
+}
+
+func (s *singleClusterProvider) GetTargetParameterName() string {
+	return ""
+}
+
+func (s *singleClusterProvider) WatchTargets(watch func() error) {
+	s.manager.WatchKubeConfig(watch)
+}
+
+func (s *singleClusterProvider) Close() {
+	s.manager.Close()
+}