#!/usr/bin/perl
use warnings;
use strict;
use Tk;

#specify interface on commandline or here
my $iface = shift || 'eth0';  #correction

my $mw = new MainWindow;
# I have my toolbar at the top, so
# I like my info boxes at the bottom
$mw->geometry('-50-50');
$mw->overrideredirect(1);
$mw->configure(-cursor => 'pirate'); #:-)

$mw->fontCreate('big',
    -family=>'courier',
    -weight=>'bold',
    -size=> 18);

my $bw = $mw->Label(-text=>'                ',
            -font=>'big',
            -bg=>'black', -fg=>'yellow')->pack
                         (-side=>'left',-fill =>'both');

# left click exits program
$mw->bind('<1>' => sub{exit});

#refresh every 1.5 seconds
my $id = Tk::After->new($mw,1500,'repeat',\&refresh);

MainLoop;

sub refresh{

my $r0 = `cat /sys/class/net/$iface/statistics/rx_bytes`;
my $t0 = `cat /sys/class/net/$iface/statistics/tx_bytes`;
tksleep($mw, 1000);
my $r1 = `cat /sys/class/net/$iface/statistics/rx_bytes`;
my $t1 = `cat /sys/class/net/$iface/statistics/tx_bytes`;

my $rr = sprintf ("%03d",($r1 - $r0)/1024);
my $tr = sprintf ("%03d",($t1 - $t0)/1024);

$bw->configure(-text=>"Rx: $rr kBs || Tx: $tr kBs");
}

sub tksleep {
  # Like sleep, but actually allows the display to be
  # updated, and takes milliseconds instead of seconds.
  # A non-blocking sleep for the eventloop
   my $mw = shift;
   my $ms = shift;
   my $flag = 0;

   $mw->after($ms, sub { $flag++ });
   $mw->waitVariable(\$flag);
}