Add changeset package

changeset is an easy way to track parent/child relationships and trigger
parent updates if child changes

pkg/changeset/changeset.go

@@ -0,0 +1,71 @@
+package changeset
+
+import (
+	"strings"
+
+	"github.com/rancher/norman/controller"
+	"k8s.io/apimachinery/pkg/runtime"
+)
+
+type Key struct {
+	Namespace string
+	Name      string
+}
+
+type ControllerProvider interface {
+	Generic() controller.GenericController
+}
+
+type Enqueuer func(namespace, name string)
+
+type Resolver func(namespace, name string, obj runtime.Object) ([]Key, error)
+
+func Watch(name string, resolve Resolver, enq Enqueuer, controllers ...ControllerProvider) {
+	for _, c := range controllers {
+		watch(name, enq, resolve, c.Generic())
+	}
+}
+
+func watch(name string, enq Enqueuer, resolve Resolver, genericController controller.GenericController) {
+	genericController.AddHandler(name, func(key string) error {
+		obj, exists, err := genericController.Informer().GetStore().GetByKey(key)
+		if err != nil {
+			return err
+		}
+
+		if !exists {
+			obj = nil
+		}
+
+		var (
+			ns   string
+			name string
+		)
+
+		parts := strings.SplitN(key, "/", 2)
+		if len(parts) == 2 {
+			ns = parts[0]
+			name = parts[1]
+		} else {
+			name = parts[0]
+		}
+
+		ro, ok := obj.(runtime.Object)
+		if !ok {
+			return nil
+		}
+
+		keys, err := resolve(ns, name, ro)
+		if err != nil {
+			return err
+		}
+
+		for _, key := range keys {
+			if key.Name != "" {
+				enq(key.Namespace, key.Name)
+			}
+		}
+
+		return nil
+	})
+}