feat: add toHierarchy utility for TreeView, RecursiveList (#2072)

Co-authored-by: Bram <bramhavers@gmail.com>

src/TreeView/index.d.ts

@@ -0,0 +1 @@
+export { default as TreeView } from "./TreeView.svelte";

src/index.js

@@ -152,3 +152,4 @@ export {
   HeaderSearch,
 } from "./UIShell";
 export { UnorderedList } from "./UnorderedList";
+export { toHierarchy } from "./utils/toHierarchy";

src/utils/toHierarchy.d.ts

@@ -0,0 +1,21 @@
+type NodeLike = {
+  id: string | number;
+  nodes?: NodeLike[];
+  [key: string]: any;
+};
+
+/** Create a hierarchical tree from a flat array. */
+export function toHierarchy<
+  T extends NodeLike,
+  K extends keyof Omit<T, "id" | "nodes">,
+>(
+  flatArray: T[] | readonly T[],
+  /**
+   * Function that returns the parent ID for a given node.
+   * @example
+   * toHierarchy(flatArray, (node) => node.parentId);
+   */
+  getParentId: (node: T) => T[K] | null,
+): (T & { nodes?: (T & { nodes?: T[] })[] })[];
+
+export default toHierarchy;

src/utils/toHierarchy.js

@@ -0,0 +1,49 @@
+// @ts-check
+/**
+ * Create a nested array from a flat array.
+ * @typedef {Object} NodeLike
+ * @property {string | number} id - Unique identifier for the node
+ * @property {NodeLike[]} [nodes] - Optional array of child nodes
+ * @property {Record<string, any>} [additionalProperties] - Any additional properties
+ *
+ * @param {NodeLike[]} flatArray - Array of flat nodes to convert
+ * @param {function(NodeLike): (string|number|null)} getParentId - Function to get parent ID for a node
+ * @returns {NodeLike[]} Hierarchical tree structure
+ */
+export function toHierarchy(flatArray, getParentId) {
+  /** @type {NodeLike[]} */
+  const tree = [];
+  const childrenOf = new Map();
+  const itemsMap = new Map(flatArray.map((item) => [item.id, item]));
+
+  flatArray.forEach((item) => {
+    const parentId = getParentId(item);
+
+    // Only create nodes array if we have children.
+    const children = childrenOf.get(item.id);
+    if (children) {
+      item.nodes = children;
+    }
+
+    // Check if parentId exists using Map instead of array lookup.
+    const parentExists = parentId && itemsMap.has(parentId);
+
+    if (parentId && parentExists) {
+      if (!childrenOf.has(parentId)) {
+        childrenOf.set(parentId, []);
+      }
+      childrenOf.get(parentId).push(item);
+
+      const parent = itemsMap.get(parentId);
+      if (parent) {
+        parent.nodes = childrenOf.get(parentId);
+      }
+    } else {
+      tree.push(item);
+    }
+  });
+
+  return tree;
+}
+
+export default toHierarchy;