# Plan: Add react-hook-form + zod for Form Validation

## Goal

Replace ad-hoc form state (`useState` per field, manual validation) with `react-hook-form`
and `zod` schemas, matching the stwaddle stack convention. Validation errors render inline
next to fields.

**Prerequisite:** Plan #12 (TanStack React Query) must be complete. Mutation hooks from
that plan are used as the submit handlers here — `useForm` `handleSubmit` calls
`mutation.mutateAsync()`.

## Current state

Forms are managed ad-hoc:
```tsx
const [newName, setNewName] = useState('');
const handleCreate = async () => {
  if (!newName.trim()) return;
  await createMutation.mutateAsync({ name: newName.trim() });
};
```

No schema validation, no field-level error messages, no loading/disabled states during
submit.

## Steps

### Phase 1 — Install

1. `npm install react-hook-form zod @hookform/resolvers` in `src/Budget.Client/`.

### Phase 2 — Create zod schemas

2. Create `src/Budget.Client/src/schemas/index.ts` with one schema per create/update request:

```ts
export const createBudgetSchema = z.object({
  name: z.string().min(1, 'Name is required').max(200),
});

export const createIncomeSchema = z.object({
  name: z.string().min(1, 'Name is required').max(200),
  frequency: z.nativeEnum(Frequency),
  amount: z.number({ invalid_type_error: 'Amount is required' }).positive('Must be positive'),
});

export const createOutgoSchema = z.object({
  name: z.string().min(1).max(200),
  category: z.string().max(100).optional(),
  type: z.nativeEnum(OutgoType),
  frequency: z.nativeEnum(Frequency),
  amount: z.number().positive(),
  paymentSource: z.string().max(100).optional(),
  notes: z.string().max(1000).optional(),
});

export const createShareSchema = z.object({
  email: z.string().email('Must be a valid email'),
  permission: z.nativeEnum(SharePermission),
});

export const updateTaxRateSchema = z.object({
  effectiveTaxRate: z.number().min(0).max(0.99),
});
```

### Phase 3 — Update forms in pages

For each form, the pattern is:

```tsx
const { register, handleSubmit, reset, formState: { errors, isSubmitting } } = useForm<CreateBudgetRequest>({
  resolver: zodResolver(createBudgetSchema),
});

const onSubmit = async (data: CreateBudgetRequest) => {
  await createBudget.mutateAsync(data);
  reset();
};

return (
  <form onSubmit={handleSubmit(onSubmit)}>
    <input {...register('name')} />
    {errors.name && <span>{errors.name.message}</span>}
    <button type="submit" disabled={isSubmitting}>Create</button>
  </form>
);
```

3. **`BudgetsPage.tsx`** — wire `createBudgetSchema` into the budget name input.
4. **`IncomePage.tsx`** — wire `createIncomeSchema` / `updateIncomeSchema` for the add and edit income forms.
5. **`OutgoPage.tsx`** — wire `createOutgoSchema` / `updateOutgoSchema` for add and edit outgo forms (this is the most complex form).
6. **`SettingsPage.tsx`** — wire `createShareSchema` for the invite form; `updateShareSchema` for the permission dropdown.
7. **`SummaryPage.tsx`** — wire `updateTaxRateSchema` for the tax rate field.

### Phase 4 — Disable submit during mutation

8. Set `disabled={isSubmitting || mutation.isPending}` on submit buttons. This prevents
   double-submits while the network request is in flight.

### Phase 5 — Build and verify

9. `npm run build` — zero TypeScript errors.
10. Manually verify that submitting an empty name shows an inline error without hitting the API.

## Key decisions

- Schemas live in a single `schemas/index.ts` for now — split into per-domain files if they grow large.
- `amount` fields: HTML `<input type="number">` returns a string; use `z.coerce.number()` or
  `valueAsNumber: true` in `register()` to get a proper number before Zod validates.
- Update schemas (for edit forms) reuse the same shape as create schemas where the fields are
  identical — they are not duplicated.
- No server-side error mapping in this plan: if the API returns 422/400 with `{ error: "..." }`,
  the global MutationCache toast (from plan #12) handles it. Field-level server errors can be
  mapped via `setError` in a future pass if needed.

## Files affected

- `package.json`
- New: `src/Budget.Client/src/schemas/index.ts`
- `src/Budget.Client/src/pages/BudgetsPage.tsx`
- `src/Budget.Client/src/pages/IncomePage.tsx`
- `src/Budget.Client/src/pages/OutgoPage.tsx`
- `src/Budget.Client/src/pages/SettingsPage.tsx`
- `src/Budget.Client/src/pages/SummaryPage.tsx`