=head3 normalize_balance

$account->normalize_balance();

Find outstanding credits and use them to pay outstanding debits

=cut

sub normalize_balance {

    my ($self) = @_;

    my $outstanding_debits  = $self->outstanding_debits;

    my $outstanding_credits = $self->outstanding_credits;

    while (     $outstanding_debits->total_outstanding > 0

            and my $credit = $outstanding_credits->next )

    {

        # there's both outstanding debits and credits

        $credit->apply( { debits => $outstanding_debits } );    # applying credit, no special offset

        $outstanding_debits = $self->outstanding_debits;

    }

    return $self;

}