fix: apply code review findings (#5)

- Fix negative pie chart values in Calculator (Math.max(0, ...))
- Unify warningCopy between Planning and public-copy.ts
- Add View Transitions API type augmentation
- Standardize QuoteBuilder Suspense fallback
- Add AGENTS.md with coding guidelines

Author: TheStreamCode

AGENTS.md

@@ -0,0 +1,161 @@
+# AGENTS.md - EasyPIVA Coding Guidelines
+
+## Build / Lint / Test Commands
+
+```bash
+# Development
+bun dev              # Start dev server on port 3000
+
+# Build & Preview
+bun run build        # Production build to dist/
+bun run preview      # Preview production build
+
+# Quality Checks
+bun run typecheck    # TypeScript check (tsc --noEmit)
+bun run lint         # ESLint check
+bun run test         # Run all tests (vitest run)
+bun run test:watch   # Watch mode for tests
+
+# Single test file
+bun test src/lib/calculations/index.test.ts
+
+# Single test by name
+bun test -- --testNamePattern="calculateForfettario"
+
+# Formatting
+bun run format       # Prettier write
+bun run format:check # Prettier check
+
+# CI pipeline
+bun run ci           # format:check + typecheck + lint + test + build
+```
+
+## Tech Stack
+
+- **React 19** + **TypeScript 5.8** + **Vite 6**
+- **Tailwind CSS v4** with `@tailwindcss/vite`
+- **Zustand** for state management (with persist middleware)
+- **React Hook Form** + **Zod** for forms and validation
+- **Recharts** for charts, **motion** (framer-motion) for animations
+- **jsPDF** + **html2canvas** for PDF export
+- **shadcn/ui** components (located in `/components/ui/`)
+
+## Project Structure
+
+```
+src/
+  pages/           # Route pages (lazy loaded)
+  components/      # React components (non-ui)
+  lib/
+    calculations/  # Pure business logic (well tested)
+    quote/         # Quote builder logic
+    fiscal-data.ts # Tax constants and ATECO categories
+    format.ts      # Currency/date formatting
+    public-copy.ts # UI text constants
+  store/           # Zustand stores
+  test/setup.ts    # Vitest setup
+components/ui/     # shadcn/ui components (Button, Input, etc.)
+```
+
+## Code Style Guidelines
+
+### Imports
+
+- Use `@/` alias for src imports: `import { Button } from '@/components/ui/button'`
+- Use `@/components/` for shadcn UI components (resolves to `./components/`)
+- Group imports: React, external libs, internal (@/), types, styles
+- Use `type` imports: `import type { ForfettarioInput } from './types'`
+
+### Formatting (Prettier)
+
+- semi: true
+- singleQuote: true
+- trailingComma: 'all'
+- printWidth: 100
+- No parentheses around single arrow function params
+
+### Types & Naming
+
+- **Types**: PascalCase, descriptive: `ForfettarioInput`, `InpsCalculation`
+- **Functions**: camelCase, verb-noun: `calculateInps`, `formatCurrency`
+- **Components**: PascalCase, noun: `Button`, `QuoteBuilder`
+- **Constants**: UPPER_SNAKE_CASE for true constants: `LIMITS.ricavi`
+- **Files**: kebab-case for utilities, PascalCase for components
+- Use explicit return types for exported functions
+- Prefer `interface` for object shapes, `type` for unions/aliases
+
+### Error Handling
+
+- Guard clauses for early returns (see `calculateInps`)
+- Use Zod for runtime validation
+- Type narrowing with `typeof` checks
+- Optional chaining for nested access: `parsed.state?.hasAcceptedDisclaimer`
+
+### Components
+
+- Use `cva` (class-variance-authority) for variant-based components
+- Forward refs where needed
+- Use `cn()` utility from `@/lib/utils` for class merging
+- Dark mode: use `dark:` prefix classes, not conditional logic
+
+### Business Logic
+
+- Keep calculations pure (no side effects)
+- Input types in `types.ts`, implementations in named files
+- Test business logic thoroughly (see `src/lib/calculations/*.test.ts`)
+- Use `DomainWarning` pattern for validation feedback
+
+### State Management
+
+- Zustand stores in `src/store/`
+- Use `persist` middleware for localStorage
+- Handle SSR safely: `typeof window === 'undefined'` checks
+
+### Testing
+
+- Vitest with jsdom environment
+- Tests alongside source files: `*.test.ts`
+- E2E tests in `tests/e2e/` (Playwright)
+- Use `@testing-library/react` for component tests
+- Mock external libs (html2canvas, localStorage)
+
+## Key Patterns
+
+### View Transitions API
+
+```typescript
+// Type augmentation exists in src/types/view-transitions.d.ts
+if (document.startViewTransition) {
+  const transition = document.startViewTransition(() => {
+    flushSync(() => toggleThemeMode());
+  });
+  transition.finished.finally(() => {
+    /* cleanup */
+  });
+}
+```
+
+### Currency Formatting
+
+```typescript
+import { formatCurrency } from '@/lib/format';
+formatCurrency(value, 0); // "€1.234"
+```
+
+### Warning Pattern
+
+```typescript
+type DomainWarning = { code: WarningCode; severity: 'warning' | 'critical' };
+// Use warningCopy from '@/lib/public-copy' for UI text
+```
+
+## Performance Notes
+
+- HMR disabled in AI Studio (DISABLE_HMR env var)
+- Lazy load pages in App.tsx
+- html2canvas is dynamically imported only when needed
+
+## Italian Language
+
+- All UI copy is in Italian
+- Comments should be in English for code clarity

src/App.tsx

@@ -74,11 +74,7 @@ export default function App() {
           <Route
             path="preventivo"
             element={
-              <Suspense
-                fallback={
-                  <div className="p-6 text-sm text-zinc-500">Caricamento preventivo...</div>
-                }
-              >
+              <Suspense fallback={<RouteFallback />}>
                 <QuoteBuilder />
               </Suspense>
             }

src/lib/public-copy.ts

@@ -8,12 +8,12 @@ export const warningCopy: Record<WarningCode, { title: string; message: string }
   'revenue-over-85000': {
     title: 'Attenzione',
     message:
-      "I ricavi ragguagliati superano 85.000€. Uscirai dal regime forfettario l'anno prossimo.",
+      "Hai superato la soglia degli 85.000€. L'anno prossimo uscirai dal regime forfettario e passerai al regime ordinario, ma per l'anno in corso mantieni i benefici fiscali.",
   },
   'revenue-over-100000': {
     title: 'CRITICO',
     message:
-      "I ricavi superano 100.000€. Uscita immediata dal regime forfettario nell'anno in corso!",
+      "Hai superato la soglia dei 100.000€. Esci IMMEDIATAMENTE dal regime forfettario nell'anno in corso. Dovrai applicare l'IVA sulle fatture successive all'incasso che ha causato il superamento.",
   },
   'employee-costs-over-limit': {
     title: 'Attenzione',

src/pages/Calculator.tsx

@@ -91,7 +91,7 @@ export default function Calculator() {
     { name: 'Contributi INPS', value: stimaInps.totale, color: 'var(--color-chart-3)' },
     {
       name: 'Costi Forfettari',
-      value: values.ricavi - redditoLordo,
+      value: Math.max(0, values.ricavi - redditoLordo),
       color: 'var(--color-chart-4)',
     },
   ];

src/pages/Planning.tsx

@@ -16,19 +16,7 @@ import {
 import { motion } from 'motion/react';
 import { buildPlanningProjection } from '@/lib/calculations';
 import { formatCurrency } from '@/lib/format';
-
-const warningCopy = {
-  'revenue-over-85000': {
-    title: 'Attenzione',
-    message:
-      "Hai superato la soglia degli 85.000€. L'anno prossimo uscirai dal regime forfettario e passerai al regime ordinario, ma per l'anno in corso mantieni i benefici fiscali.",
-  },
-  'revenue-over-100000': {
-    title: 'CRITICO',
-    message:
-      "Hai superato la soglia dei 100.000€. Esci IMMEDIATAMENTE dal regime forfettario nell'anno in corso. Dovrai applicare l'IVA sulle fatture successive all'incasso che ha causato il superamento.",
-  },
-} as const;
+import { warningCopy } from '@/lib/public-copy';
 
 const mesi = ['Gen', 'Feb', 'Mar', 'Apr', 'Mag', 'Giu', 'Lug', 'Ago', 'Set', 'Ott', 'Nov', 'Dic'];
 

src/types/view-transitions.d.ts

@@ -0,0 +1,18 @@
+/**
+ * Type augmentation for View Transitions API
+ * @see https://developer.mozilla.org/en-US/docs/Web/API/View_Transitions_API
+ */
+
+interface ViewTransition {
+  finished: Promise<void>;
+  ready: Promise<void>;
+  updateCallbackDone: Promise<void>;
+}
+
+declare global {
+  interface Document {
+    startViewTransition?(updateCallback: () => void | Promise<void>): ViewTransition;
+  }
+}
+
+export {};