add_styles_page();
$db = new db_safeguard();
/* Generate invoice number */
$inv_res = $db->query("invoices", "SELECT MAX(record_id) as max_id FROM invoices");
$inv_row = $inv_res->fetch_assoc();
$inv_no = "INV_" . str_pad((($inv_row['max_id'] ?? 0) + 1), 4, "0", STR_PAD_LEFT);
$today = date('Y-m-d');
$due = date('Y-m-d', strtotime('+30 days'));
/* Fetch stock items for datalist */
$stock_res = $db->query("stock", "SELECT item_name, item_price FROM stock ORDER BY item_name ASC");
$stock_items = [];
$datalist_options = "";
while ($stock = $stock_res->fetch_assoc()) {
$name = htmlspecialchars($stock['item_name'], ENT_QUOTES);
$price = (float) ($stock['item_price'] ?? 0);
$stock_items[] = ['name' => $name, 'price' => $price];
$datalist_options .= "