1572. In the absence of imputation by the parties, payment is imputed first to the debt that is due.
Where several debts are due, payment is imputed to the debt which the debtor has the greatest interest in paying.
Where the debtor has the same interest in paying several debts, payment is imputed to the debt that became due first; if all of the debts became due at the same time, however, payment is imputed proportionately.