Adds notes.

src/lib/hierarchy.ts

@@ -0,0 +1,37 @@
+export interface HierarchyNode {
+  id: string | null;
+  title: string | null;
+  children: Hierarchy | null;
+}
+export interface Hierarchy extends Record<string, HierarchyNode> {}
+
+function addToHierarchy(
+  tree: Hierarchy,
+  [noteId, title]: [string, string],
+): Hierarchy {
+  const path = noteId.split("/");
+  if (path.length === 0) {
+    return tree;
+  }
+
+  if (!tree[path[0]]) {
+    tree[path[0]] = { id: null, title: null, children: null };
+  }
+  let curr = tree[path[0]];
+
+  for (const node of path.slice(1)) {
+    curr.children ||= {};
+    if (!curr.children[node]) {
+      curr.children[node] = { id: null, title: null, children: null };
+    }
+    curr = curr.children[node];
+  }
+
+  curr.id = noteId;
+  curr.title = title;
+  return tree;
+}
+
+export function makeHierarchy(notes: Array<[string, string]>): Hierarchy {
+  return notes.reduce(addToHierarchy, {});
+}