head-management: add ReadOnlyHeadState

src/ifs/head_management.rs

@@ -18,7 +18,7 @@ use {
         wire::JayHeadManagerSessionV1Id,
     },
     std::{
-        cell::{Cell, RefCell},
+        cell::{Cell, Ref, RefCell},
         rc::Rc,
     },
     thiserror::Error,
@@ -94,6 +94,17 @@ pub struct HeadState {
     pub brightness: Option<f64>,
 }
 
+pub struct ReadOnlyHeadState {
+    state: Rc<RefCell<HeadState>>,
+}
+
+impl ReadOnlyHeadState {
+    #[expect(dead_code)]
+    pub fn borrow(&self) -> Ref<'_, HeadState> {
+        self.state.borrow()
+    }
+}
+
 impl HeadState {
     fn update_in_compositor_space(&mut self, wl_output: Option<GlobalName>) {
         self.in_compositor_space = false;
@@ -218,6 +229,13 @@ impl HeadManagers {
         }
     }
 
+    #[expect(dead_code)]
+    pub fn state(&self) -> ReadOnlyHeadState {
+        ReadOnlyHeadState {
+            state: self.state.clone(),
+        }
+    }
+
     pub fn handle_removed(&self) {
         for head in self.managers.lock().drain_values() {
             skip_in_transaction!(head);