Transaction CSV download

Date,Description,Amount
2024-06-15,Cash Withdrawal,-100.00
2024-06-14,Cash Deposit,250.50

async function downloadTransactions(bankAccountId, startDate, endDate, accessToken) {
  const url = new URL(
    `/embedded-banking/v1/bank-accounts/${bankAccountId}/transactions/download`,
    "https://api.tesouro.com",
  );
  url.searchParams.set("startDate", startDate);
  url.searchParams.set("endDate", endDate);

  const response = await fetch(url, {
    headers: { Authorization: `Bearer ${accessToken}` },
  });

  if (!response.ok) {
    // A 401 carries no body, so don't assume JSON — fall back to the status.
    const problem = await response.json().catch(() => null);
    throw new Error(problem?.detail ?? `Download failed with ${response.status}`);
  }

  // Rejects if the stream resets mid-download, so a truncated file never reaches the user.
  const blob = await response.blob();

  const objectUrl = URL.createObjectURL(blob);
  const anchor = document.createElement("a");
  anchor.href = objectUrl;
  anchor.download = filenameFrom(response.headers.get("Content-Disposition"));

  // Some browsers only fire a programmatic click on an anchor that's in the document.
  document.body.append(anchor);
  anchor.click();
  anchor.remove();

  // Defer the revoke so the browser has started the download before the URL goes away.
  setTimeout(() => URL.revokeObjectURL(objectUrl), 0);
}

function filenameFrom(contentDisposition) {
  const match = contentDisposition?.match(/filename="([^"]+)"/);
  return match?.[1] ?? "transactions.csv";
}