Draft widget operations

native/src/widget/operation.rs

@@ -0,0 +1,62 @@
+use crate::widget::state;
+use crate::widget::Id;
+
+pub trait Operation<T> {
+    fn container(
+        &mut self,
+        id: Option<&Id>,
+        operate_on_children: &dyn Fn(&mut dyn Operation<T>),
+    );
+
+    fn focusable(
+        &mut self,
+        _state: &mut dyn state::Focusable,
+        _id: Option<&Id>,
+    ) {
+    }
+
+    fn finish(&self) -> Outcome<T> {
+        Outcome::None
+    }
+}
+
+pub enum Outcome<T> {
+    None,
+    Some(T),
+    Chain(Box<dyn Operation<T>>),
+}
+
+pub fn focus<T>(target: Id) -> impl Operation<T> {
+    struct Focus {
+        target: Id,
+    }
+
+    impl<T> Operation<T> for Focus {
+        fn focusable(
+            &mut self,
+            state: &mut dyn state::Focusable,
+            id: Option<&Id>,
+        ) {
+            if state.is_focused() {
+                match id {
+                    Some(id) if id == &self.target => {
+                        state.focus();
+                    }
+                    _ => {
+                        state.unfocus();
+                    }
+                }
+            }
+        }
+
+        fn container(
+            &mut self,
+            _id: Option<&Id>,
+            operate_on_children: &dyn Fn(&mut dyn Operation<T>),
+        ) {
+            operate_on_children(self)
+        }
+    }
+
+    Focus { target }
+}