feat: got a minimal prototype of the diffing system

crates/ewwii/src/app.rs

@@ -321,10 +321,9 @@ impl<B: DisplayBackend> App<B> {
 
             let initiator = WindowInitiator::new(&window_def, window_args)?;
 
-            // Holds the id and the props of a widget
-            // It is crutual for supporting dynamic updates
+            // Should hold the id and the props of a widget
+            // It is critical for supporting dynamic updates
             let mut widget_reg_store = WidgetRegistry::new();
-            // note for future me: ^ this might need cloning.
 
             let root_widget = build_gtk_widget(WidgetInput::Window(window_def), &mut widget_reg_store)?;
 

crates/ewwii/src/widgets/build_widget.rs

@@ -24,6 +24,14 @@ pub fn build_gtk_widget(input: WidgetInput, widget_reg: &mut WidgetRegistry) ->
 // TODO: implement the commented lines
 fn build_gtk_widget_from_node(root_node: WidgetNode, widget_reg: &mut WidgetRegistry) -> Result<gtk::Widget> {
     let root_node2 = root_node.clone();
+
+    /*
+        When a a new widget is added to the build process,
+        make sure to update get_id_to_props_map() found in
+        `iirhai/widgetnode.rs`. It is crutial to presrve 
+        dynamic update system in ewwii.
+    */
+    
     let gtk_widget = match root_node {
         WidgetNode::Box { props, children } => build_gtk_box(props, children, widget_reg)?.upcast(),
         WidgetNode::CenterBox { props, children } => build_center_box(props, children, widget_reg)?.upcast(),

crates/ewwii/src/widgets/widget_definitions.rs

@@ -59,6 +59,13 @@ pub struct WidgetEntry {
 
 pub struct WidgetRegistry {
     widgets: HashMap<u64, WidgetEntry>,
+    stored_widget_node: Option<WidgetNode>,
+}
+
+pub enum PatchGtkWidget {
+    Create(u64, Map),
+    Update(u64, Map),
+    Remove(u64),
 }
 
 impl WidgetRegistry {
@@ -66,7 +73,28 @@ impl WidgetRegistry {
         Self { widgets: HashMap::new() }
     }
 
-    pub fn update_prop_changes(&self, id_to_props: HashMap<u64, Map>) {
+    fn diff_trees(old: Option<WidgetNode>, new: WidgetNode) -> Vec<PatchGtkWidget> {
+        let mut id_to_prop = HashMap::new();
+        let _ = get_id_to_props_map(&new_widget, &mut id_to_prop);
+    }
+
+    pub fn update_widget_tree(&mut self, new_tree: WidgetNode) {
+        let old_tree = self.stored_widget_node.take();
+
+        let patch = diff_trees(old_tree, new_tree.clone());
+
+        for op in patch {
+            match op {
+                PatchGtkWidget::Create(widget_id, props) => self.create_widget(widget_id, props),
+                PatchGtkWidget::Update(widget_id, new_props) => self.update_props(widget_id, new_props),
+                PatchGtkWidget::Remove(widget_id) => self.remove_widget(widget_id),
+            }
+        }
+
+        self.stored_widget_node = Some(new_tree);
+    }
+
+    pub fn update_props(&self, id_to_props: HashMap<u64, Map>) {
         for (id, props) in id_to_props {
             if let Some(entry) = self.widgets.get(&id) {
                 (entry.update_fn)(&props);

crates/iirhai/src/widgetnode.rs

@@ -39,7 +39,14 @@ pub enum WidgetNode {
     Enter(Vec<WidgetNode>),
 }
 
-pub fn get_id_to_props_map(root_node: &WidgetNode, id_to_props: &mut HashMap<u64, Map>) -> Result<()> {
+// Get `HashMap<widget_id, widget_prop>`
+// not exactly a get function as it mutates id_to_props
+// instead of returning any value.
+// it sounds misleading but i cant think of a better name.
+pub fn get_id_to_props_map(
+    root_node: &WidgetNode, 
+    id_to_props: &mut HashMap<u64, Map>
+) -> Result<()> {
     match root_node {
         WidgetNode::Box { props, children } => {
             insert_props(props, "Box", id_to_props)?;