function postJournal($date, $description, $lines) {
    global $pdo;

    $pdo->beginTransaction();

    $stmt = $pdo->prepare(
        "INSERT INTO journal_entries (entry_date, description) VALUES (?,?)"
    );
    $stmt->execute([$date, $description]);
    $journalId = $pdo->lastInsertId();

    foreach ($lines as $l) {
        $stmt = $pdo->prepare(
            "INSERT INTO journal_entry_lines
             (journal_entry_id, account_id, debit, credit)
             VALUES (?,?,?,?)"
        );
        $stmt->execute([
            $journalId,
            $l['account_id'],
            $l['debit'],
            $l['credit']
        ]);
    }

    $pdo->commit();
}