use new scroll in files list too

src/components/revision_files.rs

@@ -1,6 +1,7 @@
 use super::{
-    CommandBlocking, CommandInfo, Component, DrawableComponent,
-    EventState, SyntaxTextComponent,
+    utils::scroll_vertical::VerticalScroll, CommandBlocking,
+    CommandInfo, Component, DrawableComponent, EventState,
+    SyntaxTextComponent,
 };
 use crate::{
     keys::SharedKeyConfig,
@@ -16,9 +17,7 @@ use asyncgit::{
 use crossbeam_channel::Sender;
 use crossterm::event::Event;
 use filetreelist::{FileTree, FileTreeItem};
-use std::{
-    cell::Cell, collections::BTreeSet, convert::From, path::Path,
-};
+use std::{collections::BTreeSet, convert::From, path::Path};
 use tui::{
     backend::Backend,
     layout::{Constraint, Direction, Layout, Rect},
@@ -43,7 +42,7 @@ pub struct RevisionFilesComponent {
     files: Vec<TreeFile>,
     current_file: SyntaxTextComponent,
     tree: FileTree,
-    scroll_top: Cell<usize>,
+    scroll: VerticalScroll,
     revision: Option<CommitId>,
     focus: Focus,
     key_config: SharedKeyConfig,
@@ -60,7 +59,7 @@ impl RevisionFilesComponent {
         Self {
             queue: queue.clone(),
             tree: FileTree::default(),
-            scroll_top: Cell::new(0),
+            scroll: VerticalScroll::new(),
             current_file: SyntaxTextComponent::new(
                 sender,
                 key_config.clone(),
@@ -168,25 +167,22 @@ impl RevisionFilesComponent {
     fn draw_tree<B: Backend>(&self, f: &mut Frame<B>, area: Rect) {
         let tree_height = usize::from(area.height.saturating_sub(2));
 
-        let selection = self.tree.visual_selection();
-        let visual_count = selection.map_or_else(
+        self.tree.visual_selection().map_or_else(
             || {
-                self.scroll_top.set(0);
-                0
+                self.scroll.reset();
             },
             |selection| {
-                self.scroll_top.set(ui::calc_scroll_top(
-                    self.scroll_top.get(),
-                    tree_height,
+                self.scroll.update(
                     selection.index,
-                ));
-                selection.count
+                    selection.count,
+                    tree_height,
+                );
             },
         );
 
         let items = self
             .tree
-            .iterate(self.scroll_top.get(), tree_height)
+            .iterate(self.scroll.get(), tree_height)
             .map(|(item, selected)| {
                 Self::tree_item_to_span(item, &self.theme, selected)
             });
@@ -213,13 +209,7 @@ impl RevisionFilesComponent {
         );
 
         if is_tree_focused {
-            ui::draw_scrollbar(
-                f,
-                area,
-                &self.theme,
-                visual_count.saturating_sub(tree_height),
-                self.scroll_top.get(),
-            );
+            self.scroll.draw(f, area, &self.theme);
         }
     }
 }

src/components/utils/scroll_vertical.rs

@@ -21,6 +21,10 @@ impl VerticalScroll {
         self.top.get()
     }
 
+    pub fn reset(&self) {
+        self.top.set(0);
+    }
+
     pub fn update(
         &self,
         selection: usize,