fix(app): avoid unnecessary git diff header auto-scroll on collapse

2026-02-13 08:50:37 +00:00
parent b64fa4ca93
commit e9efaa8499
3 changed files with 125 additions and 1 deletions
@@ -0,0 +1,59 @@
+import { describe, expect, it } from "vitest";
+import { shouldAnchorHeaderBeforeCollapse } from "./git-diff-scroll";
+
+describe("shouldAnchorHeaderBeforeCollapse", () => {
+  it("skips anchor when header is fully visible in viewport", () => {
+    expect(
+      shouldAnchorHeaderBeforeCollapse({
+        headerOffset: 120,
+        headerHeight: 44,
+        viewportOffset: 80,
+        viewportHeight: 400,
+      })
+    ).toBe(false);
+  });
+
+  it("skips anchor when header is partially visible in viewport", () => {
+    expect(
+      shouldAnchorHeaderBeforeCollapse({
+        headerOffset: 60,
+        headerHeight: 44,
+        viewportOffset: 80,
+        viewportHeight: 300,
+      })
+    ).toBe(false);
+  });
+
+  it("anchors when header is above viewport", () => {
+    expect(
+      shouldAnchorHeaderBeforeCollapse({
+        headerOffset: 200,
+        headerHeight: 44,
+        viewportOffset: 500,
+        viewportHeight: 300,
+      })
+    ).toBe(true);
+  });
+
+  it("anchors when header is below viewport", () => {
+    expect(
+      shouldAnchorHeaderBeforeCollapse({
+        headerOffset: 600,
+        headerHeight: 44,
+        viewportOffset: 100,
+        viewportHeight: 300,
+      })
+    ).toBe(true);
+  });
+
+  it("anchors when viewport metrics are unavailable", () => {
+    expect(
+      shouldAnchorHeaderBeforeCollapse({
+        headerOffset: 0,
+        headerHeight: 44,
+        viewportOffset: 0,
+        viewportHeight: 0,
+      })
+    ).toBe(true);
+  });
+});
@@ -0,0 +1,36 @@
+interface AnchorVisibilityInput {
+  headerOffset: number;
+  headerHeight: number;
+  viewportOffset: number;
+  viewportHeight: number;
+  edgeThreshold?: number;
+}
+
+export function shouldAnchorHeaderBeforeCollapse({
+  headerOffset,
+  headerHeight,
+  viewportOffset,
+  viewportHeight,
+  edgeThreshold = 1,
+}: AnchorVisibilityInput): boolean {
+  if (
+    !Number.isFinite(headerOffset) ||
+    !Number.isFinite(headerHeight) ||
+    !Number.isFinite(viewportOffset) ||
+    !Number.isFinite(viewportHeight) ||
+    viewportHeight <= 0
+  ) {
+    // Preserve current behavior when metrics are unavailable.
+    return true;
+  }
+
+  const clampedThreshold = Math.max(0, edgeThreshold);
+  const clampedHeaderHeight = Math.max(0, headerHeight);
+  const headerStart = headerOffset;
+  const headerEnd = headerOffset + clampedHeaderHeight;
+  const viewportStart = viewportOffset + clampedThreshold;
+  const viewportEnd = viewportOffset + viewportHeight - clampedThreshold;
+  const headerVisible = headerEnd > viewportStart && headerStart < viewportEnd;
+
+  return !headerVisible;
+}