Opik Frontend

Architecture Decisions

• Routing: TanStack Router (file-based)
• Data fetching: TanStack Query (never raw fetch/useEffect)
• State: Zustand for global, React state for local
• Components: shadcn/ui + Radix UI base
• Forms: React Hook Form + Zod validation

Critical Gotchas

Never useEffect for Data Fetching

// ❌ BAD
useEffect(() => {
  fetch('/api/data').then(setData);
}, []);

// ✅ GOOD
const { data } = useQuery({
  queryKey: ['data'],
  queryFn: fetchData,
});

Selective Memoization

// ✅ USE useMemo for: complex computations, large data transforms
const filtered = useMemo(() =>
  data.filter(x => x.status === 'active').map(transform),
  [data]
);

// ✅ USE useCallback for: functions passed to children
const handleClick = useCallback(() => doSomething(id), [id]);

// ❌ DON'T memoize: simple values, primitives, local functions
const name = data?.name ?? '';  // No useMemo needed

Zustand Selectors

// ✅ GOOD - specific selector
const selectedEntity = useEntityStore(state => state.selectedEntity);

// ❌ BAD - selecting entire store causes re-renders
const { selectedEntity, filters } = useEntityStore();

Layer Architecture

ui → shared → pages-shared → pages (one-way only)

• No circular dependencies
• No cross-page imports
• After modifying imports: npm run deps:validate

State Location Decisions

• URL state: filters, pagination, selected items
• Zustand: user preferences, cross-component state
• React state: form inputs, UI toggles

Component Structure

const Component: React.FC<Props> = ({ prop }) => {
  // 1. State hooks
  // 2. Queries/mutations
  // 3. Memoization (only when needed)
  // 4. Event handlers

  if (isLoading) return <Loader />;
  if (error) return <ErrorComponent />;

  return <div>...</div>;
};

Query Patterns

// Query with params
const { data } = useQuery({
  queryKey: [ENTITY_KEY, params],
  queryFn: (context) => fetchEntity(context, params),
});

// Mutation with invalidation
const mutation = useMutation({
  mutationFn: updateEntity,
  onSuccess: () => {
    queryClient.invalidateQueries({ queryKey: [ENTITY_KEY] });
  },
});

Reference Files

• forms.md - React Hook Form + Zod patterns
• ui-components.md - Button variants, typography, dark theme
• responsive-design.md - Tailwind breakpoints vs useIsPhone
• testing.md - When to test, Vitest patterns
• code-quality.md - Lodash imports, naming, deps:validate
• performance.md - Bundle optimization, rendering, memoization