I think I actually have a good foundation for a tree here.

src/day07/file_tree.rs

@@ -1,22 +1,87 @@
 #![allow(unused)]
-use std::{rc::{Weak, Rc}, cell::RefCell};
+use std::{
+    cell::RefCell,
+    ops::Deref,
+    rc::{Rc, Weak},
+};
+
+// #[derive(Debug)]
+// pub struct NodeRef(Rc<RefCell<Node>>);
 
 #[derive(Debug)]
+pub struct FileRef(Rc<RefCell<File>>);
+
+#[derive(Debug)]
+pub struct DirRef(Rc<RefCell<Dir>>);
+#[derive(Debug)]
+pub struct WeakDirRef(Weak<RefCell<Dir>>);
+
+#[derive(Debug)]
+pub enum Node {
+    Dir(DirRef),
+    File(FileRef),
+}
+
+#[derive(Debug)]
+pub struct File {
+    parent: WeakDirRef,
+    pub name: String,
+    pub size: usize,
+}
+
+#[derive(Debug, Default)]
 pub struct Dir {
-    parent: Option<Weak<RefCell<Dir>>>,
-    name: String,
-    children: Vec<Rc<RefCell<FileOrDir>>>
+    parent: Option<WeakDirRef>,
+    pub name: String,
+    children: Vec<Node>,
 }
 
-#[derive(Debug)]
-pub struct File{
-    dir: Weak<RefCell<Dir>>,
-    size: usize,
-    name: String
+impl DirRef {
+    //impling it on the ref makes the recursion a bit easier.
+    fn total_size(&self) -> usize {
+        self.0
+            .borrow()
+            .deref()
+            .children
+            .iter()
+            .map(|f| match f {
+                Node::Dir(dir) => dir.total_size(),
+                Node::File(file) => file.0.borrow().size,
+            })
+            .sum()
+    }
+    fn new(name: String) -> Self {
+        DirRef(Rc::new(RefCell::new(Dir {
+            parent: None,
+            name,
+            children: Vec::new(),
+        })))
+    }
+
+    //needs to be impled on the ref because of the need to get a weak backreference to self.
+    fn add(&self, node: Node) {
+        match node {
+            Node::Dir(ref dir) => {
+                dir.0.borrow_mut().parent = Some(WeakDirRef(Rc::downgrade(&self.0)))
+            }
+            Node::File(ref file) => file.0.borrow_mut().parent = WeakDirRef(Rc::downgrade(&self.0)),
+        }
+        self.0.borrow_mut().children.push(node);
+    }
 }
 
-#[derive(Debug)]
-pub enum FileOrDir{
-    File(File),
-    Dir(Dir),
+impl File {
+    fn get_parent(&self)-> &WeakDirRef {
+        &self.parent
+    }
+}
+
+impl Dir {
+    fn get_children(&self) -> &[Node] {
+        &self.children
+    }
+
+    fn get_parent(&self) -> &Option<WeakDirRef> {
+        &self.parent
+    }
 }