1 files changed, 138 insertions, 0 deletions
diff --git a/frontend-vanilla/src/regression.test.ts b/frontend-vanilla/src/regression.test.ts
new file mode 100644
index 0000000..2512f3f
--- /dev/null
+++ b/frontend-vanilla/src/regression.test.ts
@@ -0,0 +1,138 @@
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { store } from './store';
+import { apiFetch } from './api';
+import { updateItem, fetchItems, renderItems } from './main';
+
+// Mock api
+vi.mock('./api', () => ({
+    apiFetch: vi.fn()
+}));
+
+// Mock main module functions that we aren't testing directly but are imported/used
+// Note: We need to use vi.importActual to get the real implementations we want to test
+// But main.ts has side effects and complex DOM manipulations, so we might want to mock parts of it.
+// Mock IntersectionObserver
+class MockIntersectionObserver {
+    observe = vi.fn();
+    unobserve = vi.fn();
+    disconnect = vi.fn();
+}
+vi.stubGlobal('IntersectionObserver', MockIntersectionObserver);
+
+describe('Scroll-to-Read Regression Tests', () => {
+    beforeEach(() => {
+        document.body.innerHTML = '<div id="app"><div id="main-content"><div id="content-area"></div></div></div>';
+        // Mock scrollIntoView
+        Element.prototype.scrollIntoView = vi.fn();
+        vi.clearAllMocks();
+        store.setItems([]);
+
+        // Setup default auth response
+        vi.mocked(apiFetch).mockResolvedValue({
+            ok: true,
+            status: 200,
+            json: async () => []
+        } as Response);
+    });
+
+    afterEach(() => {
+        vi.useRealTimers();
+    });
+
+    it('should mark item as read when existing in store and scrolled past', async () => {
+        vi.useRealTimers();
+        const mockItem = {
+            _id: 999,
+            title: 'Regression Test Item',
+            read: false,
+            url: 'http://example.com/regression',
+            publish_date: '2023-01-01'
+        } as any;
+
+        store.setItems([mockItem]);
+
+        // Manually trigger the render logic that sets up the listener (implied by renderItems/init in real app)
+        // Here we can't easily trigger the exact closure in main.ts without fully initializing it.
+        // However, we can simulate the "check logic" if we extract it or replicate the test conditions
+        // that the previous main.test.ts used.
+
+        // Since we are mocking the scroll behavior on the DOM element which main.ts attaches to:
+        const mainContent = document.getElementById('main-content');
+        expect(mainContent).not.toBeNull();
+
+        // We need to invoke renderItems to attach the listener
+        renderItems();
+
+        // Mock getBoundingClientRect for container
+        if (mainContent) {
+            mainContent.getBoundingClientRect = vi.fn(() => ({
+                top: 0, bottom: 800, height: 800, left: 0, right: 0, width: 0, x: 0, y: 0, toJSON: () => { }
+            }));
+        }
+
+        // Mock getBoundingClientRect for item (scrolled past top: -50)
+        // renderItems creates the DOM elements based on store
+        const itemEl = document.querySelector(`.feed-item[data-id="999"]`);
+        expect(itemEl).not.toBeNull();
+
+        if (itemEl) {
+            itemEl.getBoundingClientRect = vi.fn(() => ({
+                top: -50, bottom: 50, height: 100, left: 0, right: 0, width: 0, x: 0, y: 0, toJSON: () => { }
+            }));
+        }
+
+        // Prepare API mock
+        vi.mocked(apiFetch).mockResolvedValue({ ok: true } as Response);
+
+        // Trigger scroll event
+        mainContent?.dispatchEvent(new Event('scroll'));
+
+        // Wait for throttle (250ms) + buffer
+        await new Promise(resolve => setTimeout(resolve, 300));
+
+        // Verify API call
+        expect(apiFetch).toHaveBeenCalledWith(expect.stringContaining('/api/item/999'), expect.objectContaining({
+            method: 'PUT',
+            body: expect.stringContaining('"read":true')
+        }));
+    });
+
+    it('should NOT mark item as read if NOT scrolled past', async () => {
+        vi.useRealTimers();
+        const mockItem = {
+            _id: 888,
+            title: 'Visible Test Item',
+            read: false,
+            url: 'http://example.com/visible',
+            publish_date: '2023-01-01'
+        } as any;
+
+        store.setItems([mockItem]);
+        renderItems();
+
+        const mainContent = document.getElementById('main-content');
+
+        // Container
+        if (mainContent) {
+            mainContent.getBoundingClientRect = vi.fn(() => ({
+                top: 0, bottom: 800, height: 800, left: 0, right: 0, width: 0, x: 0, y: 0, toJSON: () => { }
+            }));
+        }
+
+        // Item is still visible (top: 100)
+        const itemEl = document.querySelector(`.feed-item[data-id="888"]`);
+        if (itemEl) {
+            itemEl.getBoundingClientRect = vi.fn(() => ({
+                top: 100, bottom: 200, height: 100, left: 0, right: 0, width: 0, x: 0, y: 0, toJSON: () => { }
+            }));
+        }
+
+        vi.mocked(apiFetch).mockResolvedValue({ ok: true } as Response);
+
+        mainContent?.dispatchEvent(new Event('scroll'));
+        await new Promise(resolve => setTimeout(resolve, 300));
+
+        // API should NOT be called
+        expect(apiFetch).not.toHaveBeenCalledWith(expect.stringContaining('/api/item/888'), expect.anything());
+    });
+});