quote_columns

sub quote_columns {
  my ($self, @columns) = @_;
  my @quoted_columns = ();
  state $sql_date_re = do {
    my $format = quotemeta(quotemeta($self->quote('__FORMAT__')));
    my $sql = quotemeta($self->sql_date_format('__COLUMN__', '__FORMAT__'));
    $sql =~ s/__COLUMN__/(.+)/;
    $sql =~ s/$format/(.+)/;
    $sql;
  };
  warn $sql_date_re;


  foreach (@columns) {
    if (/^\w+$/) {
      push @quoted_columns, $self->quote_identifier($_);
    }
    elsif (my ($t, $c) = /^(\w+)\.(\w+)$/) {
      push @quoted_columns,
        $self->quote_identifier($t) . "." . $self->quote_identifier($c);
    }
    elsif (my ($expr, $alias) = /^\s*(.+?)\s+AS\s+(\w+)\s*$/i) {
      push @quoted_columns, $self->quote_columns($expr) . " AS " . $self->quote_identifier($alias);
    }
    elsif (my ($column, $format) = /$sql_date_re/) {
      push @quoted_columns, $self->sql_date_format($self->quote_columns($column), $format);
    }
    else {
      die "unable to quote column: $_";
    }
  }
  return join(", ", @quoted_columns);
}