Noções Básicas de Modularidade

npm install express@5 zod
npm install -D typescript@5.6 tsx

// infrastructure/http/orders-router.ts
import express from "express";
import { createOrder } from "../../application/create-order";
 
export const ordersRouter = express.Router();
 
ordersRouter.post("/", async (req, res, next) => {
  try {
    const order = await createOrder(req.body);
    res.status(201).json({ data: order });
  } catch (err) {
    next(err);
  }
});

// application/create-order.ts
import type { OrderRepository } from "../domain/ports/order-repository";
 
export type CreateOrderDeps = { orders: OrderRepository };
 
export async function createOrder(
  deps: CreateOrderDeps,
  input: { customerId: string; sku: string; qty: number }
) {
  if (input.qty <= 0) throw new Error("INVALID_QTY");
  const order = { id: crypto.randomUUID(), ...input, status: "pending" as const };
  await deps.orders.save(order);
  return order;
}

// domain/ports/order-repository.ts
export type Order = {
  id: string;
  customerId: string;
  sku: string;
  qty: number;
  status: "pending" | "shipped";
};
 
export interface OrderRepository {
  save(order: Order): Promise<void>;
  findById(id: string): Promise<Order | null>;
}

Permitido:
  infrastructure/http  -> application -> domain
 
Proibido:
  domain -> express
  domain -> infrastructure
  application -> tipo Request do express

// main.ts
import express from "express";
import { ordersRouter } from "./infrastructure/http/orders-router";
import { PostgresOrderRepository } from "./infrastructure/postgres-order-repository";
import { createOrderHandler } from "./infrastructure/http/create-order-handler";
 
const orders = new PostgresOrderRepository(pool);
const app = express();
app.use(express.json());
app.use("/orders", createOrderHandler({ orders }));
app.listen(3000);

src/
├── modules/orders/     # módulo de recurso - possui regras de pedido
├── modules/billing/
└── shared/
    ├── errors.ts       # classe base AppError
    └── logger.ts       # instância pino

import { describe, it, expect } from "node:test";
import { createOrder } from "../application/create-order";
 
describe("createOrder", () => {
  it("salva pedido válido", async () => {
    const saved: unknown[] = [];
    const orders = { save: async (o: unknown) => { saved.push(o); }, findById: async () => null };
    const result = await createOrder({ orders }, { customerId: "c1", sku: "SKU1", qty: 2 });
    expect(result.status).toBe("pending");
    expect(saved).toHaveLength(1);
  });
});