#!/usr/bin/perl -w
use strict;
use Getopt::Long;

my $sshcommand    ;
my $sshconfigfilename ;
my $netcatcommand ;
my $netcatoptions ;
my $machine       ;

my $result = GetOptions (
  "config=s"         => \$sshconfigfilename,
  "machine=s"        => \$machine,
  "help"             => \&help, 
  "sshcommand=s"     => \$sshcommand,
  "netcatcommand=s"  => \$netcatcommand,
  "netcatoptions=s"  => \$netcatoptions,
); 

$sshconfigfilename = "$ENV{HOME}/.ssh/config" unless defined($sshconfigfilename);
$machine       = $ENV{GRID_REMOTE_MACHINE} unless defined($machine);

parseSSHConfig();

$sshcommand    = 'ssh'                     unless defined($sshcommand);
$netcatcommand = 'netcat'                  unless defined($netcatcommand);
$netcatoptions = '-v -l -p 1234'           unless defined($netcatoptions);

help() unless defined($machine);

my $command = "$sshcommand $machine $netcatcommand $netcatoptions";
print "Connected to '$machine' via '$sshcommand' using '$netcatcommand' with options '$netcatoptions'\n";
exec($command);

sub parseSSHConfig {

  local $/ = undef;
  open(my $con, $sshconfigfilename);
    my $c = <$con>; 
  close($con);
  
  $c =~ /^\s*(Host.*$machine(?:.|\n)*?)(?:Host\b|\z)/m;
  my $hostdesc = $1;

  if (defined($hostdesc)) {

    $sshcommand    = $1 if !$sshcommand    and !$hostdesc =~ /^#gm\s+sshcommand\s+'([^'\n]*)'/m;

    $netcatcommand = $1 if !$netcatcommand and $hostdesc =~ /^#gm\s+netcat(?:command)?\s+'([^'\n]*)'/m;

    $netcatoptions = $1 if !$netcatoptions and $hostdesc =~ /^#gm\s+netcatopt(?:ions)?\s+'([^'\n]*)'/m;

    $machine       = $1 if $hostdesc =~ /^\s*HostName\s+([\w.-]+)/m;
  }
}

sub help {

  print <<"INFO";
Usage: $0 [--sshcommand 'ssh'] [--netcatcommand 'netcat'] [--netcatoptions netcatoptions] [--config configfile] [--machine machine]

  By default, machine is given by environment variable \$GRID_REMOTE_MACHINE
  By default, sshcommand is 'ssh'
  By default, netcatcommand is 'netcat'
  By default, netcatoptions is '-v -l -p 1234'
  By default, configfile is '~/.ssh/config'

Algorithm:
  The program connects via 'ssh' to machine 'machine'
  and executes there the 'netcat' command in 'listen' mode
  using the 'port' specified by the 'netcatoptions'.
INFO
  exit(0);
}