1use crate::sum_tree::{self, SumTree};
 2use parking_lot::Mutex;
 3use std::sync::Arc;
 4
 5use crate::ElementBox;
 6
 7pub struct List {
 8    state: ListState,
 9}
10
11pub struct ListState(Arc<Mutex<StateInner>>);
12
13struct StateInner {
14    elements: Vec<ElementBox>,
15    element_heights: SumTree<ElementHeight>,
16}
17
18#[derive(Clone, Debug)]
19enum ElementHeight {
20    Pending,
21    Ready(f32),
22}
23
24#[derive(Clone, Debug, Default)]
25struct ElementHeightSummary {
26    pending_count: usize,
27    height: f32,
28}
29
30impl sum_tree::Item for ElementHeight {
31    type Summary = ElementHeightSummary;
32
33    fn summary(&self) -> Self::Summary {
34        todo!()
35    }
36}
37
38impl sum_tree::Summary for ElementHeightSummary {
39    type Context = ();
40
41    fn add_summary(&mut self, summary: &Self, cx: &Self::Context) {
42        self.pending_count += summary.pending_count;
43        self.height += summary.height;
44    }
45}