(server) Add New Parameter And Functions for Select Subscriber

Summary:
- add type to represent the returned component tree
```
expected data:
{
  [nodeID1]: [subtree1],
  [nodeID2]: [subtree2],
  ...
}
example:
{
   id1: {
    id2: {
      id3: {
        id4: {},
        id5: {
          id6: {}
        }
      }
    }
  }
}
```
- add functions to deal with a tree
  - `_getElementLeaves` for finding ids that don't have any child given the tree structure
  - `_getPathForNode` for finding path (similar to previous path parameter) for given id
- This diff still retain functionality in case of selector appear to touch only one element.

Reviewed By: mweststrate

Differential Revision: D21040427

fbshipit-source-id: e6704535a437ad47d9664cc16896b9f24c9d6736

desktop/plugins/layout/Inspector.tsx

@@ -25,6 +25,8 @@ type GetNodesOptions = {
   forAccessibilityEvent?: boolean;
 };
 
+type ElementSelectorNode = {[id: string]: ElementSelectorNode};
+
 type Props = {
   ax?: boolean;
   client: PluginClient;
@@ -131,8 +133,12 @@ export default class Inspector extends Component<Props> {
 
     this.props.client.subscribe(
       this.call().SELECT,
-      ({path}: {path: Array<ElementID>}) => {
-        this.getAndExpandPath(path);
+      ({path, tree}: {path?: Array<ElementID>; tree?: ElementSelectorNode}) => {
+        if (tree) {
+          this._getAndExpandPathFromTree(tree);
+        } else if (path) {
+          this.getAndExpandPath(path);
+        }
       },
     );
 
@@ -291,6 +297,48 @@ export default class Inspector extends Component<Props> {
     this.onElementSelected(path[path.length - 1]);
   }
 
+  getElementLeaves(tree: ElementSelectorNode): Array<ElementID> {
+    return tree
+      ? Object.entries(tree).reduce(
+          (
+            currLeafNode: Array<ElementID>,
+            [id, children]: [ElementID, ElementSelectorNode],
+          ): Array<ElementID> =>
+            currLeafNode.concat(
+              Object.keys(children).length > 0
+                ? this.getElementLeaves(children)
+                : [id],
+            ),
+          [],
+        )
+      : [];
+  }
+
+  /// Return path from given tree structure and id if id is not null; otherwise return any path
+  getPathForNode(
+    tree: ElementSelectorNode,
+    nodeID: ElementID | null,
+  ): Array<ElementID> | null {
+    for (const node in tree) {
+      if (
+        node === nodeID ||
+        (nodeID === null && Object.keys(tree[node]).length == 0)
+      ) {
+        return [node];
+      }
+      const path = this.getPathForNode(tree[node], nodeID);
+      if (path !== null) {
+        return [node].concat(path);
+      }
+    }
+    return null;
+  }
+
+  // NOTE: this will be used in the future when we remove path and use tree instead
+  async _getAndExpandPathFromTree(tree: ElementSelectorNode) {
+    this.getAndExpandPath(this.getPathForNode(tree, null) ?? []);
+  }
+
   onElementSelected = debounce((selectedKey: ElementID) => {
     this.onElementHovered(selectedKey);
     this.props.onSelect(selectedKey);