API Rules

app.get("/invoices", async (req, res) => {
  const limit = Math.min(Number(req.query.limit ?? 20), 100);
  const cursor = req.query.cursor as string | undefined;
  const page = await listInvoices({ limit, cursor });
  res.json({ data: page.items, nextCursor: page.nextCursor });
});
 
app.post("/invoices", async (req, res) => {
  const key = req.headers["idempotency-key"];
  if (!key) return res.status(400).json({ error: { code: "missing_idempotency_key", message: "required" } });
  // ...
});

// src/errors/http-error.ts
export class HttpError extends Error {
  constructor(
    public status: number,
    public code: string,
    message: string,
  ) {
    super(message);
  }
}
 
export function errorHandler(err: unknown, _req: express.Request, res: express.Response, _next: express.NextFunction) {
  if (err instanceof HttpError) {
    return res.status(err.status).json({ error: { code: err.code, message: err.message } });
  }
  res.status(500).json({ error: { code: "internal_error", message: "unexpected error" } });
}

// src/routes/invoices.ts
app.get("/v1/invoices", async (req, res, next) => {
  try {
    const limit = Math.min(Math.max(Number(req.query.limit ?? 20), 1), 100);
    const result = await repo.list({ limit, cursor: req.query.cursor as string | undefined });
    res.json({ data: result.rows, nextCursor: result.nextCursor });
  } catch (e) {
    next(e);
  }
});
 
app.post("/v1/invoices", async (req, res, next) => {
  try {
    const idempotencyKey = req.headers["idempotency-key"];
    if (typeof idempotencyKey !== "string") {
      throw new HttpError(400, "missing_idempotency_key", "Idempotency-Key header required");
    }
    const existing = await repo.findByIdempotencyKey(idempotencyKey);
    if (existing) return res.status(200).json({ data: existing });
    const created = await repo.create({ ...req.body, idempotencyKey });
    res.status(201).json({ data: created });
  } catch (e) {
    next(e);
  }
});