Authz: Refactor folder tree (#99554)

* Refactor folder tree to its own structure

* Make it possible to json encode the tree

* Use iterations for Ancestors and Children

---------

Co-authored-by: IevaVasiljeva <ieva.vasiljeva@grafana.com>

pkg/services/authz/rbac/tree.go

@@ -0,0 +1,108 @@
+package rbac
+
+import (
+	"iter"
+
+	"github.com/grafana/grafana/pkg/services/authz/rbac/store"
+)
+
+func newFolderTree(folders []store.Folder) folderTree {
+	t := folderTree{
+		Index: make(map[string]int, len(folders)),
+		Nodes: make([]folderNode, 0, len(folders)),
+	}
+
+	for _, f := range folders {
+		t.Insert(f.UID, f.ParentUID)
+	}
+
+	return t
+}
+
+type folderTree struct {
+	// All nodes for the folderTree.
+	Nodes []folderNode
+	// Index is a map of folderNode UID to its positons in Nodes.
+	Index map[string]int
+}
+
+type folderNode struct {
+	// UID is the uniqiue identifier for folderNode
+	UID string
+	// Parent is the position into folderTree nodes for parent, we store -1 for nodes that don't have a parent.
+	Parent int
+	// Children is positons into folderTree nodes for all children.
+	Children []int
+}
+
+func (t *folderTree) Insert(uid string, parentUID *string) int {
+	parent := -1
+	if parentUID != nil {
+		// find parent
+		i, ok := t.Index[*parentUID]
+		if !ok {
+			// insert parent if it don't exists yet
+			i = t.Insert(*parentUID, nil)
+		}
+		parent = i
+	}
+
+	i, ok := t.Index[uid]
+	if !ok {
+		// this node does not exist yet so we add it to the index and append the new node
+		i = len(t.Nodes)
+		t.Index[uid] = i
+		t.Nodes = append(t.Nodes, folderNode{
+			UID:    uid,
+			Parent: parent,
+		})
+	} else {
+		// if a node is added as a parent node first, its parent will not be set, so we make sure to do it now
+		t.Nodes[i].Parent = parent
+	}
+
+	if parent != -1 {
+		// update parent to include the index of new child node
+		t.Nodes[parent].Children = append(t.Nodes[parent].Children, i)
+	}
+
+	return i
+}
+
+// Ancestors returns an iterator that yields ancestors for uid
+func (t *folderTree) Ancestors(uid string) iter.Seq[folderNode] {
+	current, ok := t.Index[uid]
+	if !ok {
+		return func(yield func(folderNode) bool) {}
+	}
+
+	current = t.Nodes[current].Parent
+	return func(yield func(folderNode) bool) {
+		for {
+			if current == -1 || !yield(t.Nodes[current]) {
+				return
+			}
+
+			current = t.Nodes[current].Parent
+		}
+	}
+}
+
+// Children returns an iterator that yields all children for uid
+func (t *folderTree) Children(uid string) iter.Seq[folderNode] {
+	current, ok := t.Index[uid]
+	if !ok {
+		return func(yield func(folderNode) bool) {}
+	}
+
+	queue := t.Nodes[current].Children
+	return func(yield func(folderNode) bool) {
+		for len(queue) > 0 {
+			current, queue = queue[0], queue[1:]
+			if !yield(t.Nodes[current]) {
+				return
+			}
+			queue = append(queue, t.Nodes[current].Children...)
+		}
+	}
+}