fix(post): avoid duplicate history entries on OP permalinks

src/lib/utils/__tests__/thread-scroll-utils.test.ts

@@ -0,0 +1,122 @@
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { clearThreadScrollSpacer, openThreadAtTop } from '../thread-scroll-utils';
+
+const appendThreadContainer = (cid: string, top = 240) => {
+  const element = document.createElement('div');
+  element.dataset.threadContainerCid = cid;
+  element.getBoundingClientRect = () =>
+    ({
+      bottom: top + 100,
+      height: 100,
+      left: 0,
+      right: 100,
+      top,
+      width: 100,
+    }) as DOMRect;
+  document.body.appendChild(element);
+  return element;
+};
+
+describe('thread-scroll-utils', () => {
+  let scrollToMock: ReturnType<typeof vi.fn>;
+  let requestAnimationFrameMock: ReturnType<typeof vi.fn>;
+
+  beforeEach(() => {
+    vi.clearAllMocks();
+
+    scrollToMock = vi.fn();
+    requestAnimationFrameMock = vi.fn((callback: FrameRequestCallback) => {
+      callback(0);
+      return 1;
+    });
+
+    Object.defineProperty(window, 'scrollTo', {
+      configurable: true,
+      value: scrollToMock,
+      writable: true,
+    });
+    Object.defineProperty(window, 'requestAnimationFrame', {
+      configurable: true,
+      value: requestAnimationFrameMock,
+      writable: true,
+    });
+    Object.defineProperty(window, 'scrollY', {
+      configurable: true,
+      value: 0,
+      writable: true,
+    });
+    Object.defineProperty(window, 'innerHeight', {
+      configurable: true,
+      value: 100,
+      writable: true,
+    });
+    Object.defineProperty(document.documentElement, 'scrollHeight', {
+      configurable: true,
+      value: 200,
+      writable: true,
+    });
+  });
+
+  afterEach(() => {
+    clearThreadScrollSpacer();
+    document.body.innerHTML = '';
+  });
+
+  it('scrolls the current thread without pushing duplicate history entries', () => {
+    appendThreadContainer('thread-cid');
+    const navigateMock = vi.fn();
+
+    expect(
+      openThreadAtTop({
+        cid: 'thread-cid',
+        currentPathname: '/mu/thread/thread-cid',
+        navigate: navigateMock,
+        threadRoute: '/mu/thread/thread-cid',
+      }),
+    ).toBe(true);
+
+    expect(navigateMock).not.toHaveBeenCalled();
+    expect(requestAnimationFrameMock).toHaveBeenCalledOnce();
+    expect(scrollToMock).toHaveBeenCalledTimes(2);
+    expect(scrollToMock).toHaveBeenNthCalledWith(1, {
+      behavior: 'auto',
+      left: 0,
+      top: 240,
+    });
+  });
+
+  it('navigates to the OP thread before scrolling when the route differs', () => {
+    appendThreadContainer('thread-cid');
+    const navigateMock = vi.fn();
+
+    expect(
+      openThreadAtTop({
+        cid: 'thread-cid',
+        currentPathname: '/mu/thread/reply-cid',
+        navigate: navigateMock,
+        threadRoute: '/mu/thread/thread-cid',
+      }),
+    ).toBe(true);
+
+    expect(navigateMock).toHaveBeenCalledWith('/mu/thread/thread-cid');
+    expect(requestAnimationFrameMock).toHaveBeenCalledOnce();
+    expect(scrollToMock).toHaveBeenCalledTimes(2);
+  });
+
+  it('returns false when the permalink cannot resolve a thread target', () => {
+    const navigateMock = vi.fn();
+
+    expect(
+      openThreadAtTop({
+        cid: undefined,
+        currentPathname: '/mu/thread/thread-cid',
+        navigate: navigateMock,
+        threadRoute: '/mu/thread/thread-cid',
+      }),
+    ).toBe(false);
+
+    expect(navigateMock).not.toHaveBeenCalled();
+    expect(requestAnimationFrameMock).not.toHaveBeenCalled();
+    expect(scrollToMock).not.toHaveBeenCalled();
+  });
+});