Periodic statements

// `grid` is your authenticated HTTP client for the Grid base URL.
// ERROR_RESOLUTION_NOTICE, maskAccountNumber, and the delivery helpers are yours.

// Follow nextCursor until hasMore is false
async function* listAll(path, params) {
  let cursor;
  do {
    const query = new URLSearchParams({ ...params, limit: '100' });
    if (cursor) query.set('cursor', cursor);
    const page = await grid.get(`${path}?${query}`);
    yield* page.data;
    cursor = page.hasMore ? page.nextCursor : undefined;
  } while (cursor);
}

async function buildStatement(customerId, accountId, startDate, endDate) {
  const customer = await grid.get(`/customers/${customerId}`);
  const commercial = customer.customerType === 'BUSINESS';

  let account;
  for await (const candidate of listAll('/customers/internal-accounts', { customerId })) {
    if (candidate.id === accountId) {
      account = candidate;
      break;
    }
  }
  if (!account) throw new Error(`Account ${accountId} does not belong to customer ${customerId}`);

  // Card rows are listed by customer; keep the ones funded by this account
  const window = { startDate, endDate, sortOrder: 'asc' };
  async function* periodRows() {
    for await (const tx of listAll('/transactions', { ...window, accountIdentifier: accountId })) {
      if (tx.type !== 'CARD') yield tx;
    }
    for await (const tx of listAll('/transactions', { ...window, customerId, type: 'CARD' })) {
      if (tx.accountId === accountId) yield tx;
    }
  }

  // One line per settled movement
  const lines = [];
  for await (const tx of periodRows()) {
    const sign = tx.direction === 'CREDIT' ? 1 : -1;

    if (tx.type === 'CARD') {
      if (tx.status !== 'SETTLED' && tx.status !== 'PARTIALLY_SETTLED') continue;
      lines.push({
        date: tx.authorizedAt,
        type: 'CARD',
        direction: tx.direction,
        payee: tx.merchant.descriptor,
        terminalLocation:
          !commercial && tx.merchant.city && tx.merchant.state
            ? `${tx.merchant.city}, ${tx.merchant.state}`
            : undefined,
        amount: sign * tx.settledAmount.amount,
      });
      continue;
    }

    if (tx.status !== 'COMPLETED') continue;

    if (tx.type === 'INCOMING') {
      lines.push({
        date: tx.settledAt,
        type: 'INCOMING',
        direction: tx.direction,
        payee: tx.description,
        amount: sign * tx.receivedAmount.amount,
      });
      continue;
    }

    // OUTGOING: sentAmount already includes fees, so split it into two lines
    const fees = tx.fees ?? 0;
    lines.push({
      date: tx.settledAt,
      type: 'OUTGOING',
      direction: tx.direction,
      payee: tx.description,
      amount: sign * (tx.sentAmount.amount - fees),
    });
    if (fees > 0) {
      lines.push({ date: tx.settledAt, type: 'FEE', direction: tx.direction, amount: sign * fees });
    }
  }
  lines.sort((a, b) => a.date.localeCompare(b.date)); // oldest first across both lists

  const closingBalance = account.totalBalance.amount;
  const openingBalance = await previousClosingBalance(accountId); // from your records, same unit
  const movement = lines.reduce((sum, line) => sum + line.amount, 0);
  if (openingBalance + movement !== closingBalance) {
    throw new Error('Statement does not reconcile: opening balance plus lines is not the closing balance');
  }
  const totalFees = -lines
    .filter((line) => line.type === 'FEE')
    .reduce((sum, line) => sum + line.amount, 0);

  const { currency } = account.totalBalance;
  const format = (amount) => (amount / 10 ** currency.decimals).toFixed(currency.decimals);

  const statement = {
    // Disclosures: a consumer statement carries the notice, a commercial statement the contact line
    providerLine:
      'This account is held at Lead Bank, the account-holding institution. ' +
      'Lightspark is the program manager and is not a bank.',
    ...(commercial
      ? { contactLine: 'Direct inquiries to 8605 Santa Monica Blvd, PMB 64461, West Hollywood, CA 90069 or (855) 516-0103.' }
      : { errorResolutionNotice: ERROR_RESOLUTION_NOTICE }), // the notice includes the phone number and mailing address
    // Account fields
    accountHolder: commercial ? customer.businessInfo.legalName : customer.fullName,
    accountType: account.type, // render as a label, for example "Consumer prepaid account"
    accountNumber: maskAccountNumber(account.fundingPaymentInstructions),
    period: { startDate, endDate },
    issueDate: new Date().toISOString(),
    openingBalance: format(openingBalance),
    closingBalance: format(closingBalance),
    lines: lines.map((line) => ({ ...line, amount: format(line.amount) })),
    totalFees: format(totalFees),
  };

  await sendStatementEmail(customer.platformCustomerId, statement); // your delivery channel
  await recordStatementDelivery(accountId, statement.issueDate);
}