NestedFolderPicker: Migrate to app platform API (#106926)

* Add /children endpoint

* Update folder client

* Add comment

* Add feature toggle

* Add new version of useFoldersQuery

* Error handling

* Format

* Rename feature toggle

* Remove options and move root folder constant

* Fix feature toggle merge

* Add feature toggle again

* Rename useFoldersQuery files

* Update API spec

* Fix test

* Add test

* Better typings

---------

Co-authored-by: Clarity-89 <homes89@ukr.net>

pkg/registry/apis/folders/register.go

@@ -192,6 +192,11 @@ func (b *FolderAPIBuilder) UpdateAPIGroupInfo(apiGroupInfo *genericapiserver.API
 	storage[resourceInfo.StoragePath("counts")] = &subCountREST{searcher: b.searcher}
 	storage[resourceInfo.StoragePath("access")] = &subAccessREST{b.folderSvc, b.ac}
 
+	// Adds a path to return children of a given folder
+	storage[resourceInfo.StoragePath("children")] = &subChildrenREST{
+		lister: storage[resourceInfo.StoragePath()].(rest.Lister),
+	}
+
 	apiGroupInfo.VersionedResourcesStorageMap[folders.VERSION] = storage
 	b.storage = storage[resourceInfo.StoragePath()].(grafanarest.Storage)
 	return nil

pkg/registry/apis/folders/sub_children.go

@@ -0,0 +1,73 @@
+package folders
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+
+	"k8s.io/apimachinery/pkg/apis/meta/internalversion"
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/apiserver/pkg/registry/rest"
+
+	folders "github.com/grafana/grafana/apps/folder/pkg/apis/folder/v1beta1"
+)
+
+type subChildrenREST struct {
+	lister rest.Lister
+}
+
+var _ = rest.Connecter(&subChildrenREST{})
+var _ = rest.StorageMetadata(&subChildrenREST{})
+
+// RootFolderName Hardcoded magic const to get root folders without parent.
+var RootFolderName = "general"
+
+func (r *subChildrenREST) New() runtime.Object {
+	return &folders.FolderList{}
+}
+
+func (r *subChildrenREST) Destroy() {
+}
+
+func (r *subChildrenREST) ProducesMIMETypes(verb string) []string {
+	return nil
+}
+
+func (r *subChildrenREST) ProducesObject(verb string) interface{} {
+	return &folders.FolderList{}
+}
+
+func (r *subChildrenREST) ConnectMethods() []string {
+	return []string{"GET"}
+}
+
+func (r *subChildrenREST) NewConnectOptions() (runtime.Object, bool, string) {
+	return nil, false, "" // true means you can use the trailing path as a variable
+}
+
+func (r *subChildrenREST) Connect(ctx context.Context, name string, opts runtime.Object, responder rest.Responder) (http.Handler, error) {
+	obj, err := r.lister.List(ctx, &internalversion.ListOptions{})
+	if err != nil {
+		return nil, err
+	}
+	allFolders, ok := obj.(*folders.FolderList)
+	if !ok {
+		return nil, fmt.Errorf("could not list folders")
+	}
+
+	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
+		children := &folders.FolderList{}
+		parentName := ""
+
+		if name != RootFolderName {
+			parentName = name
+		}
+		for _, folder := range allFolders.Items {
+			if parentName == getParent(&folder) {
+				children.Items = append(children.Items, folder)
+			}
+		}
+
+		responder.Object(http.StatusOK, children)
+	}), nil
+}