From 8da6faa74bc36064ea1511ebd99b1162f4ceffe8 Mon Sep 17 00:00:00 2001
From: Vincent Chan <okcdz@diverse.space>
Date: Wed, 3 Aug 2022 19:35:37 +0800
Subject: [PATCH] feat: node traverser

---
 .../lib/document/node_traverser.dart          | 42 +++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 frontend/app_flowy/packages/flowy_editor/lib/document/node_traverser.dart

diff --git a/frontend/app_flowy/packages/flowy_editor/lib/document/node_traverser.dart b/frontend/app_flowy/packages/flowy_editor/lib/document/node_traverser.dart
new file mode 100644
index 0000000000..b4005f054a
--- /dev/null
+++ b/frontend/app_flowy/packages/flowy_editor/lib/document/node_traverser.dart
@@ -0,0 +1,42 @@
+import 'package:flowy_editor/document/node.dart';
+
+import './state_tree.dart';
+import './node.dart';
+
+/// [NodeTraverser] is used to traverse the nodes in visual order.
+class NodeTraverser {
+  final StateTree stateTree;
+  Node? currentNode;
+
+  NodeTraverser(this.stateTree, Node beginNode) : currentNode = beginNode;
+
+  Node? next() {
+    final node = currentNode;
+    if (node == null) {
+      return null;
+    }
+
+    if (node.children.isNotEmpty) {
+      currentNode = _findLeadingChild(node);
+    } else if (node.next != null) {
+      currentNode = node.next!;
+    } else {
+      final parent = node.parent!;
+      final nextOfParent = parent.next;
+      if (nextOfParent == null) {
+        currentNode = null;
+      } else {
+        currentNode = _findLeadingChild(node);
+      }
+    }
+
+    return node;
+  }
+
+  Node _findLeadingChild(Node node) {
+    while (node.children.isNotEmpty) {
+      node = node.children.first;
+    }
+    return node;
+  }
+}