sub draw_graph {
    my ( $filename, @data ) = @_;
    my $graph = new GD::Graph::histogram( 400, 600 );
    $graph->set(
        x_label           => 'Data',
        y_label           => 'Count',
        title             => 'A Histogram Chart',
        x_labels_vertical => 1,
        bar_spacing       => 0,
        shadow_depth      => 1,
        shadowclr         => 'dred',
        transparent       => 0,
      )
      or warn $graph->error;

    my $gd = $graph->plot( \@data ) or die $graph->error;

    open( IMG, '>' . $filename ) or die $!;
    binmode IMG;
    print IMG $gd->png;
}