# ADR-0005 Phase 3 Implementation Summary

**Date**: 2026-01-08
**Status**: ✅ Complete

## Overview

Successfully completed Phase 3 of ADR-0005 enforcement by creating all mutation hooks for data modifications using TanStack Query mutations.

## Files Created

### Mutation Hooks

All mutation hooks follow a consistent pattern:
- Automatic cache invalidation via `queryClient.invalidateQueries()`
- Success/error notifications via notification service
- Proper TypeScript types for parameters
- Comprehensive JSDoc documentation with examples

#### Watched Items Mutations

1. **[src/hooks/mutations/useAddWatchedItemMutation.ts](../src/hooks/mutations/useAddWatchedItemMutation.ts)**
   - Adds an item to the user's watched items list
   - Parameters: `{ itemName: string, category?: string }`
   - Invalidates: `['watched-items']` query

2. **[src/hooks/mutations/useRemoveWatchedItemMutation.ts](../src/hooks/mutations/useRemoveWatchedItemMutation.ts)**
   - Removes an item from the user's watched items list
   - Parameters: `{ masterItemId: number }`
   - Invalidates: `['watched-items']` query

#### Shopping List Mutations

3. **[src/hooks/mutations/useCreateShoppingListMutation.ts](../src/hooks/mutations/useCreateShoppingListMutation.ts)**
   - Creates a new shopping list
   - Parameters: `{ name: string }`
   - Invalidates: `['shopping-lists']` query

4. **[src/hooks/mutations/useDeleteShoppingListMutation.ts](../src/hooks/mutations/useDeleteShoppingListMutation.ts)**
   - Deletes an entire shopping list
   - Parameters: `{ listId: number }`
   - Invalidates: `['shopping-lists']` query

5. **[src/hooks/mutations/useAddShoppingListItemMutation.ts](../src/hooks/mutations/useAddShoppingListItemMutation.ts)**
   - Adds an item to a shopping list
   - Parameters: `{ listId: number, item: { masterItemId?: number, customItemName?: string } }`
   - Supports both master items and custom items
   - Invalidates: `['shopping-lists']` query

6. **[src/hooks/mutations/useUpdateShoppingListItemMutation.ts](../src/hooks/mutations/useUpdateShoppingListItemMutation.ts)**
   - Updates a shopping list item (quantity, notes, purchased status)
   - Parameters: `{ itemId: number, updates: Partial<ShoppingListItem> }`
   - Updatable fields: `custom_item_name`, `quantity`, `is_purchased`, `notes`
   - Invalidates: `['shopping-lists']` query

7. **[src/hooks/mutations/useRemoveShoppingListItemMutation.ts](../src/hooks/mutations/useRemoveShoppingListItemMutation.ts)**
   - Removes an item from a shopping list
   - Parameters: `{ itemId: number }`
   - Invalidates: `['shopping-lists']` query

#### Barrel Export

8. **[src/hooks/mutations/index.ts](../src/hooks/mutations/index.ts)**
   - Centralized export for all mutation hooks
   - Easy imports: `import { useAddWatchedItemMutation } from '../hooks/mutations'`

## Mutation Hook Pattern

All mutation hooks follow this consistent structure:

```typescript
export const useSomeMutation = () => {
  const queryClient = useQueryClient();

  return useMutation({
    mutationFn: async (params) => {
      const response = await apiClient.someMethod(params);

      if (!response.ok) {
        const error = await response.json().catch(() => ({
          message: `Request failed with status ${response.status}`,
        }));
        throw new Error(error.message || 'Failed to perform action');
      }

      return response.json();
    },
    onSuccess: () => {
      // Invalidate affected queries
      queryClient.invalidateQueries({ queryKey: ['some-query'] });
      notifySuccess('Action completed successfully');
    },
    onError: (error: Error) => {
      notifyError(error.message || 'Failed to perform action');
    },
  });
};
```

## Usage Examples

### Adding a Watched Item

```tsx
import { useAddWatchedItemMutation } from '../hooks/mutations';

function WatchedItemsManager() {
  const addWatchedItem = useAddWatchedItemMutation();

  const handleAdd = () => {
    addWatchedItem.mutate(
      { itemName: 'Milk', category: 'Dairy' },
      {
        onSuccess: () => console.log('Added to watched list!'),
        onError: (error) => console.error('Failed:', error),
      }
    );
  };

  return (
    <button
      onClick={handleAdd}
      disabled={addWatchedItem.isPending}
    >
      {addWatchedItem.isPending ? 'Adding...' : 'Add to Watched List'}
    </button>
  );
}
```

### Managing Shopping Lists

```tsx
import {
  useCreateShoppingListMutation,
  useAddShoppingListItemMutation,
  useUpdateShoppingListItemMutation
} from '../hooks/mutations';

function ShoppingListManager() {
  const createList = useCreateShoppingListMutation();
  const addItem = useAddShoppingListItemMutation();
  const updateItem = useUpdateShoppingListItemMutation();

  const handleCreateList = () => {
    createList.mutate({ name: 'Weekly Groceries' });
  };

  const handleAddItem = (listId: number, masterItemId: number) => {
    addItem.mutate({
      listId,
      item: { masterItemId }
    });
  };

  const handleMarkPurchased = (itemId: number) => {
    updateItem.mutate({
      itemId,
      updates: { is_purchased: true }
    });
  };

  return (
    <div>
      <button onClick={handleCreateList}>Create List</button>
      {/* ... other UI */}
    </div>
  );
}
```

## Benefits Achieved

### Performance
- ✅ **Automatic cache updates** - Queries automatically refetch after mutations
- ✅ **Request deduplication** - Multiple mutation calls are properly queued
- ✅ **Optimistic updates ready** - Infrastructure in place for Phase 4

### Code Quality
- ✅ **Standardized pattern** - All mutations follow the same structure
- ✅ **Comprehensive documentation** - JSDoc with examples for every hook
- ✅ **Type safety** - Full TypeScript types for all parameters
- ✅ **Error handling** - Consistent error handling and user notifications

### Developer Experience
- ✅ **React Query Devtools** - Inspect mutation states in real-time
- ✅ **Easy imports** - Barrel export for clean imports
- ✅ **Consistent API** - Same pattern across all mutations
- ✅ **Built-in loading states** - `isPending`, `isError`, `isSuccess` states

### User Experience
- ✅ **Automatic notifications** - Success/error toasts on all mutations
- ✅ **Fresh data** - Queries automatically update after mutations
- ✅ **Loading states** - UI can show loading indicators during mutations
- ✅ **Error feedback** - Clear error messages on failures

## Current State

### Completed
- ✅ All 7 mutation hooks created
- ✅ Barrel export created for easy imports
- ✅ Comprehensive documentation with examples
- ✅ Consistent error handling and notifications
- ✅ Automatic cache invalidation on all mutations

### Not Yet Migrated

The following custom hooks still use the old `useApi` pattern with manual state management:

1. **[src/hooks/useWatchedItems.tsx](../src/hooks/useWatchedItems.tsx)** (74 lines)
   - Uses `useApi` for add/remove operations
   - Manually updates state via `setWatchedItems`
   - Should be refactored to use mutation hooks

2. **[src/hooks/useShoppingLists.tsx](../src/hooks/useShoppingLists.tsx)** (222 lines)
   - Uses `useApi` for all CRUD operations
   - Manually updates state via `setShoppingLists`
   - Complex manual state synchronization logic
   - Should be refactored to use mutation hooks

These hooks are actively used throughout the application and will need careful refactoring in Phase 4.

## Remaining Work

### Phase 4: Hook Refactoring & Cleanup

#### Step 1: Refactor useWatchedItems
- [ ] Replace `useApi` calls with mutation hooks
- [ ] Remove manual state management logic
- [ ] Simplify to just wrap mutation hooks with custom logic
- [ ] Update all tests

#### Step 2: Refactor useShoppingLists
- [ ] Replace `useApi` calls with mutation hooks
- [ ] Remove manual state management logic
- [ ] Remove complex state synchronization
- [ ] Keep `activeListId` state (still needed)
- [ ] Update all tests

#### Step 3: Remove Deprecated Code
- [ ] Remove `setWatchedItems` from UserDataContext
- [ ] Remove `setShoppingLists` from UserDataContext
- [ ] Remove `useApi` hook (if no longer used)
- [ ] Remove `useApiOnMount` hook (already deprecated)

#### Step 4: Add Optimistic Updates (Optional)
- [ ] Implement optimistic updates for better UX
- [ ] Use `onMutate` to update cache before server response
- [ ] Implement rollback on error

#### Step 5: Documentation & Testing
- [ ] Update all component documentation
- [ ] Update developer onboarding guide
- [ ] Add integration tests for mutation flows
- [ ] Create migration guide for other developers

## Testing Recommendations

Before considering Phase 4:

1. **Manual Testing**
   - Add/remove watched items
   - Create/delete shopping lists
   - Add/remove/update shopping list items
   - Verify cache updates correctly
   - Check success/error notifications

2. **React Query Devtools**
   - Open devtools in development
   - Watch mutations execute
   - Verify cache invalidation
   - Check mutation states (pending, success, error)

3. **Network Tab**
   - Verify API calls are correct
   - Check request/response payloads
   - Ensure no duplicate requests

4. **Error Scenarios**
   - Test with network offline
   - Test with invalid data
   - Verify error notifications appear
   - Check cache remains consistent

## Migration Path for Components

Components currently using `useWatchedItems` or `useShoppingLists` can continue using them as-is. When we refactor those hooks in Phase 4, the component interface will remain the same.

For new components, you can use mutation hooks directly:

```tsx
// Old way (still works)
import { useWatchedItems } from '../hooks/useWatchedItems';

function MyComponent() {
  const { addWatchedItem, removeWatchedItem } = useWatchedItems();
  // ...
}

// New way (recommended for new code)
import { useAddWatchedItemMutation, useRemoveWatchedItemMutation } from '../hooks/mutations';

function MyComponent() {
  const addWatchedItem = useAddWatchedItemMutation();
  const removeWatchedItem = useRemoveWatchedItemMutation();
  // ...
}
```

## Documentation Updates

- [x] Created [Phase 3 Summary](./adr-0005-phase-3-summary.md)
- [ ] Update [ADR-0005](../docs/adr/0005-frontend-state-management-and-server-cache-strategy.md) (mark Phase 3 complete)
- [ ] Update component documentation (Phase 4)
- [ ] Update developer onboarding guide (Phase 4)

## Conclusion

Phase 3 successfully created all mutation hooks following TanStack Query best practices. The application now has a complete set of standardized mutation operations with automatic cache invalidation and user notifications.

**Next Steps**: Proceed to Phase 4 to refactor existing custom hooks (`useWatchedItems` and `useShoppingLists`) to use the new mutation hooks, then remove deprecated state setters and cleanup old code.