fix(ui): keep diff refreshes targeted

packages/ui/src/components/views/diffScrollAnchor.ts

@@ -0,0 +1,35 @@
+export type DiffScrollAnchor = {
+  path: string;
+  topOffset: number;
+};
+
+export const findDiffScrollAnchor = (
+  rootTop: number,
+  sections: Array<{ path: string; top: number }>,
+): DiffScrollAnchor | null => {
+  if (sections.length === 0) return null;
+
+  let beforeTop: { path: string; top: number } | null = null;
+  let afterTop: { path: string; top: number } | null = null;
+  for (const section of sections) {
+    if (section.top <= rootTop) {
+      if (!beforeTop || section.top > beforeTop.top) beforeTop = section;
+    } else if (!afterTop || section.top < afterTop.top) {
+      afterTop = section;
+    }
+  }
+
+  const anchor = beforeTop ?? afterTop;
+  if (!anchor) return null;
+  return { path: anchor.path, topOffset: anchor.top - rootTop };
+};
+
+export const getRestoredDiffScrollTop = (
+  scrollTop: number,
+  previousTopOffset: number,
+  currentTopOffset: number,
+  maxScrollTop: number,
+): number => Math.min(
+  Math.max(0, maxScrollTop),
+  Math.max(0, scrollTop + currentTopOffset - previousTopOffset),
+);