Validate product name uniqueness

src/screens/ManageProductsScreen.test.tsx

@@ -165,6 +165,35 @@ describe('ManageProductsScreen barcode lookup', () => {
     expect(mockDb.products.add).not.toHaveBeenCalled();
   });
 
+  it('prevents adding a product with a duplicate name (case-insensitive)', async () => {
+    mockUseProducts.mockReturnValue([
+      {
+        id: 'prod-1',
+        name: 'Existing Product',
+        category: 'Snacks',
+        barcode: undefined,
+        unit_type: 'unit',
+        bulk_name: 'pack',
+        archived: false,
+        created_at: 0,
+        updated_at: 0,
+      },
+    ]);
+
+    const user = userEvent.setup();
+    render(
+      <MemoryRouter>
+        <ManageProductsScreen />
+      </MemoryRouter>,
+    );
+
+    await user.type(screen.getByLabelText(/name/i), 'existing product');
+    await user.click(screen.getByRole('button', { name: /save product/i }));
+
+    expect(await screen.findByText(/product with this name already exists/i)).toBeVisible();
+    expect(mockDb.products.add).not.toHaveBeenCalled();
+  });
+
   it('informs the user when barcode lookup happens offline', async () => {
     const originalNavigator = navigator;
     Object.defineProperty(globalThis, 'navigator', {
@@ -237,6 +266,55 @@ describe('ManageProductsScreen barcode lookup', () => {
     });
     expect(mockDb.products.update).not.toHaveBeenCalled();
   });
+
+  it('prevents updating a product to use an existing name', async () => {
+    mockUseProducts.mockReturnValue([
+      {
+        id: 'prod-1',
+        name: 'Existing Product',
+        category: 'Snacks',
+        barcode: '123456',
+        unit_type: 'unit',
+        bulk_name: 'pack',
+        archived: false,
+        created_at: 0,
+        updated_at: 0,
+      },
+      {
+        id: 'prod-2',
+        name: 'Another Product',
+        category: 'Snacks',
+        barcode: '654321',
+        unit_type: 'unit',
+        bulk_name: 'pack',
+        archived: false,
+        created_at: 0,
+        updated_at: 0,
+      },
+    ]);
+
+    const user = userEvent.setup();
+    render(
+      <MemoryRouter>
+        <ManageProductsScreen />
+      </MemoryRouter>,
+    );
+
+    await user.click(screen.getByLabelText(/edit another product/i));
+    const nameField = screen
+      .getAllByLabelText(/name/i)
+      .find((input) => (input as HTMLInputElement).value === 'Another Product');
+    expect(nameField).toBeDefined();
+    fireEvent.change(nameField as Element, { target: { value: 'Existing Product' } });
+    expect(nameField).toHaveValue('Existing Product');
+    await user.click(screen.getByLabelText(/save product/i));
+
+    await waitFor(() => {
+      expect(nameField).toHaveAccessibleDescription('A product with this name already exists.');
+      expect(nameField).toHaveAttribute('aria-invalid', 'true');
+    });
+    expect(mockDb.products.update).not.toHaveBeenCalled();
+  });
 });
 
 describe('ManageProductsScreen auto-adding products to pick lists', () => {

src/screens/ManageProductsScreen.tsx

@@ -33,6 +33,7 @@ export const ManageProductsScreen = () => {
   const [category, setCategory] = useState('');
   const [barcode, setBarcode] = useState('');
   const [barcodeError, setBarcodeError] = useState('');
+  const [nameError, setNameError] = useState('');
   const [scannerOpen, setScannerOpen] = useState(false);
   const [lookupStatus, setLookupStatus] = useState<'idle' | 'loading' | 'found' | 'notfound' | 'offline'>(
     'idle',
@@ -78,6 +79,19 @@ export const ManageProductsScreen = () => {
     [products],
   );
 
+  const findNameConflict = useCallback(
+    (value?: string, productId?: string) => {
+      if (!value) return undefined;
+
+      const normalizedValue = value.trim().toLowerCase();
+
+      return products.find(
+        (product) => product.id !== productId && product.name.trim().toLowerCase() === normalizedValue,
+      );
+    },
+    [products],
+  );
+
   const assertUniqueBarcode = useCallback(
     async (value?: string, productId?: string) => {
       if (!value) return;
@@ -94,6 +108,22 @@ export const ManageProductsScreen = () => {
     [db.products, findBarcodeConflict],
   );
 
+  const assertUniqueName = useCallback(
+    async (value: string, productId?: string) => {
+      const normalized = value.trim().toLowerCase();
+      if (!normalized) return;
+
+      const conflict = findNameConflict(value, productId);
+
+      if (conflict) {
+        const error = new Error('A product with this name already exists.');
+        error.name = 'DuplicateNameError';
+        throw error;
+      }
+    },
+    [findNameConflict],
+  );
+
   const addProductToAutoLists = useCallback(
     async (product: Product, timestamp: number) => {
       const pickLists = await db.pickLists.toArray();
@@ -167,8 +197,13 @@ export const ManageProductsScreen = () => {
     if (!name || !category) return;
 
     try {
+      await assertUniqueName(name);
       await assertUniqueBarcode(barcode || undefined);
     } catch (error) {
+      if (error instanceof Error && error.name === 'DuplicateNameError') {
+        setNameError(error.message);
+        return;
+      }
       if (error instanceof Error && error.name === 'DuplicateBarcodeError') {
         setBarcodeError(error.message);
         return;
@@ -195,6 +230,7 @@ export const ManageProductsScreen = () => {
     });
     setName('');
     setBarcode('');
+    setNameError('');
     setFeedback({ text: 'Product added.', severity: 'success' });
   };
 
@@ -206,6 +242,7 @@ export const ManageProductsScreen = () => {
       barcode?: string;
     },
   ) => {
+    await assertUniqueName(updates.name, productId);
     await assertUniqueBarcode(updates.barcode, productId);
 
     await db.products.update(productId, {
@@ -251,12 +288,23 @@ export const ManageProductsScreen = () => {
           <TextField
             label="Name"
             value={name}
-            onChange={(event) => setName(event.target.value)}
+            onChange={(event) => {
+              setName(event.target.value);
+              setNameError('');
+            }}
+            error={Boolean(nameError)}
+            helperText={nameError || undefined}
             InputProps={
               name
                 ? {
                     endAdornment: (
-                      <Button onClick={() => setName('')} size="small">
+                      <Button
+                        onClick={() => {
+                          setName('');
+                          setNameError('');
+                        }}
+                        size="small"
+                      >
                         Clear
                       </Button>
                     ),