# Tech Stack & Build System

## Stack

| Layer | Technology |
|-------|-----------|
| Backend | Node.js 18+, Express 5 |
| Database | PostgreSQL (via `pg` pool in `backend/db.js`) |
| Auth | bcryptjs, cookie-based sessions (httpOnly, 24h expiry) |
| File uploads | Multer 2 (10MB limit) |
| Frontend | React 19 (Create React App / react-scripts 5) |
| Frontend serving | Express serves `frontend/build/` as static files on port 3001 |
| UI Icons | lucide-react |
| Charts | recharts |
| Spreadsheet parsing | xlsx (frontend), pandas + openpyxl (backend Python scripts) |
| Markdown rendering | react-markdown |
| Diagrams | mermaid |

## Architecture: Single-Port Serving

Express on port 3001 serves **both** the API and the production frontend build:
- API routes: `/api/*` — handled by Express route handlers
- Frontend: everything else — served as static files from `frontend/build/`

There is no separate frontend server in production. The React dev server (`npm start` on port 3000) is only for local development with hot-reload. In production and on the dev server, you must run `npm run build` in `frontend/` after any frontend code change, then restart the backend.

**After editing frontend source files:**
```bash
cd frontend && npm run build    # Compile new bundle into frontend/build/
# Then restart backend (or it will serve the new static files on next request)
```

The CI/CD pipeline handles this automatically — `build-frontend` stage runs before deploy.

## Common Commands

### Backend
```bash
cd backend
node setup.js          # Initialize DB, tables, indexes, default admin user
node server.js         # Start backend on port 3001 (serves API + frontend build)
```

### Frontend
```bash
cd frontend
npm install            # Install dependencies
npm run build          # Production build → frontend/build/ (REQUIRED after code changes)
npm start              # Dev server on port 3000 (local dev only, NOT used in production)
npm test               # Run tests (react-scripts test)
```

### Both servers (from project root)
```bash
./start-servers.sh     # Start backend + frontend in background
./stop-servers.sh      # Stop all servers
```

### Database Migrations (run from `backend/`)
```bash
node migrations/run-all.js    # Runs all migrations in order (idempotent)
```

### Python Scripts (from `backend/scripts/`)
```bash
# Compliance xlsx parsing (called automatically by upload flow)
python3 parse_compliance_xlsx.py <file>

# Bulk notes import
python3 import_notes_from_csv.py input.csv --dry-run
python3 import_notes_from_csv.py input.csv
```

Python dependencies: `pandas>=2.0.0`, `openpyxl>=3.0.0` (install via apt or venv).

## Environment Configuration

- `backend/.env` — PORT, CORS_ORIGINS, SESSION_SECRET, NVD_API_KEY, Ivanti API credentials
- `frontend/.env` — REACT_APP_API_BASE, REACT_APP_API_HOST
- Both `.env` files are gitignored; see `.env.example` files for templates.
- React env vars are baked in at **build time** — you must rebuild (`npm run build`) after changing them.

## Code Style & Lint Rules

### Unused Variables

The frontend ESLint config enforces `no-unused-vars` as a warning. The CI pipeline fails if warnings exceed 25. To avoid lint failures:

- **Prefix intentionally-unused variables with `_`** — this suppresses the warning. The `varsIgnorePattern: "^_"` and `argsIgnorePattern: "^_"` rules are configured in `frontend/package.json`.
- Common patterns:
  - `const [_unused, setFoo] = useState(...)` — destructured value you don't need
  - `const _legacyRef = useRef(...)` — kept for future use
  - `function handler(_event) { ... }` — required parameter signature but unused
- **Do not leave variables unprefixed if unused.** Either use them, remove them, or prefix with `_`.
- This applies to all frontend code written by the agent.

### Backend

No ESLint is configured for backend — the pipeline uses `node -c` syntax checking only. Keep code clean but there is no automated unused-var enforcement on the backend side.

## Ports

| Environment | URL | Notes |
|---|---|---|
| Production / Dev server | http://IP:3001 | Express serves API + static frontend build |
| Local dev (frontend only) | http://localhost:3000 | React dev server with hot-reload, proxies API to :3001 |
