$in = s/^\((.*)\)$/$1/;
my @splat = split(/,/, $in);
my ( $depth, $left );
while ( my $c = shift @splat ) {
     $left .= ( $left ? ',' : '' ) . $c;
     ++$depth if index($c, '(') >= $[;
     --$depth if index($c, ')') >= $[;
     last if $depth == 0;
}
my $right = join(',', @splat);