public function rules()
{
if ($this->action == ACTION_ARCHIVE) {
return [];
}
$invoiceId = $this->entity()->id;
$rules = ['invoice_items' => 'valid_invoice_items', 'invoice_number' => 'unique:invoices,invoice_number,' . $invoiceId . ',id,account_id,' . $this->user()->account_id, 'discount' => 'positive'];
return $rules;
}