#! /usr/bin/perl

use strict;
use warnings;
use English qw( -no_match_vars );
use WWW::Mechanize;

use constant TRUE => 1;

{
    usage() if @ARGV != 2;        
    
    my $url       = shift;
    my $data_file = shift;
    
    my ($fj, $start, $end, $spent, $gap, $date, $resp);
    
    my $fh;
    
    open( $fh, '>', $data_file ) or die "Unable to open '$data_file' : $OS_ERROR";
    
    my $mech = WWW::Mechanize->new();
    
    while ( TRUE ) {
        
        my($hour, $min) = (localtime())[2,1];        
        $date           = sprintf("%02d:%02d", $hour, $min);
        
        $start = time();
        $resp  = undef;
        if( eval { $resp = $mech->get($url); 1 } ) {
            $end   = time();
            $spent = $end - $start;
        } else {
            $spent = undef;           
        }

        print $fh "$date\t" . (defined($spent) ? $spent : 'undef') . "\n";
        print "$date\t" . (defined($spent) ? $spent : 'undef') . "\n";

        if( $spent ) {
            $gap = ( $spent >= 30  ? 0 : 30 - $spent );
        } else {
            $gap = 30;   
        }
                
        sleep $gap;
    }
    
}

sub usage {
 
    print <<"EOF";
    
  Usage: $PROGRAM_NAME <url> <outfile>
  
  Fetch <url> and write the time spent (in seconds) into <outfile>. 
  
  URL is fetched every 30 seconds. The time spent fetching the URL is 
  subtracted from the sleeped time and is set to zero if it exceeds
  30 seconds.
  
  Timing infor is printed into the outfile and STDOUT in the following
  format:
  
    hour:min\\t<seconds>
    
  For example
  
    13:53   0
    13:54   1    
          
EOF

    exit 1;
}