#!/usr/bin/perl -w
#
# A script to change the IP/hostname on a cluster machine
# jdreed@mit.edu

use strict;
use Socket;
use File::Copy;
use Getopt::Std;

# sulogin gets upset if it gets a ^C
$SIG{'INT'} = 'bail';

my $MASKS="/usr/share/debathena-recovery-mode-config/masks";

if (defined($ARGV[0]) && ($ARGV[0] eq 'test')) {
    print "Change IP address or hostname\n";
    exit 0;
}

sub confirm {
    my $question = shift || "Continue?";
    print "${question} (y/n) ";
    my $ans = <STDIN>;
    return ($ans =~ m/^y$/i);
}

sub bail {
    if ($_[0] eq 'INT') {
	print "\nCancelled.";
    } else {
	print shift;
    }
    print "\n\n(press ENTER to return to the recovery mode menu)\n";
    my $dummy = <STDIN>;
    exit 0;
}

sub mask {
    my $ip = shift;
    my $mask = shift;
    my $mbits = pack("B*", (1 x $mask) . (0 x (32 - $mask)));
    my $ibits = pack("CCCC", split(/\./, $ip));
    my $net = $ibits & $mbits;
    return join('.', unpack("CCCC", $net));
}

sub cidr2ip {
    my $cidr = shift;
    return join('.', unpack("CCCC", pack("B*", (1 x $cidr) . (0 x (32 - $cidr)))));
}

sub validIP {
    my $ip = shift;
    if ($ip =~ /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/) {
	if (scalar(grep { ($_ <= 255) && ($_ >= 0) } ($1, $2, $3, $4)) == 4) {
	    return 1;
	}
    }
    return 0;
}

# main

# Sanity checks
foreach (qw(/etc/network/interfaces /etc/hosts /etc/hostname)) {
    (-w $_) || bail("Cannot write to $_. (Are you root?)");
}

(-r $MASKS) || bail("Cannot read $MASKS");

my $machtype = `machtype -L`;
chomp($machtype);
if ($machtype ne 'debathena-cluster') {
    print "WARNING: This script is designed for debathena-cluster machines but\n";
    print "this machine is running $machtype.\n";
    confirm("Are you SURE you want to continue?") || bail("OK, cancelled.");
}

my $ip = '';
until (validIP($ip)) {
    if ($ip) {
	print "Invalid IP address ($ip).  Try again.\n";
    }
    print "Enter the new IP address: ";
    ($ip = <STDIN>) =~ s/\s//g;
}
print "Looking up hostname...";
my $fqdn = gethostbyaddr(inet_aton($ip), AF_INET);
if ($fqdn) {
    print " found.\n";
} else {
    $fqdn = '';
    print " not found.\n";
    until ($fqdn =~ /^[a-z][\w\-\.]*/i) {
	print "Please enter the machine's new hostname: ";
	($fqdn = <STDIN>) =~ s/\s//g;
    }
}
$fqdn = lc($fqdn);
my $hostname = $fqdn;
if ($fqdn =~ /\./) {
    $hostname = (split(/\./, $fqdn))[0];
} else {
    print "NOTE: No domain specified, assuming 'mit.edu'";
    $fqdn = "${hostname}.mit.edu";
}

my ($subnetmask, $gateway);
print "Looking up netmask information...\n";
open(MASKS, $MASKS) || bail("Cannot read $MASKS: $!");
while (<MASKS>) {
    next if (/^#/);
    next unless (/\d/);
    my ($addr, $sbits, $mbits, $gw) = split(' '); #the ' ' pattern emulates awk
    if (mask($ip, $sbits) eq $addr) {
	$subnetmask = cidr2ip($mbits);
	if (! $gw) {
	    my @octets = split(/\./, mask($ip, $mbits));
	    my $trailing = pop(@octets) + 1;
	    $gateway = join('.', @octets, $trailing);
	} else {
	    $gateway = $gw;
	}
	last;
    }
}
(defined($subnetmask) && defined($gateway)) || bail("Could not find a matching line in masks file for $ip.\nIf you are sure you typed the IP address correctly, please report\nthis error to IS&T, along with the IP address you were trying to use.");

close(MASKS);
print "IP address:  $ip\n";
print "Subnet Mask: $subnetmask\n";
print "Gateway:     $gateway\n";
print "Hostname:    $hostname\n";
print "FQDN:        $fqdn\n\n";

confirm("Does that look correct?") || bail("OK, cancelled.");

print "Updating /etc/network/interfaces...\n";
copy("/etc/network/interfaces", "/etc/network/interfaces.old") || bail("Could not copy /etc/network/interfaces");
open(INTERFACES, ">/etc/network/interfaces") || bail ("Could not overwrite /etc/network/interfaces: $!");
print INTERFACES <<"ENDINTERFACES";
# This file was created by $0

# The loopback interface
auto lo
iface lo inet loopback

# The primary network interface
auto eth0
iface eth0 inet static
        address $ip
        netmask $subnetmask
        gateway $gateway
        dns-nameservers 18.70.0.160 18.71.0.151 18.72.0.3
ENDINTERFACES
close(INTERFACES);

print "Updating /etc/hosts...\n";

copy("/etc/hosts", "/etc/hosts.old") || bail("Could not copy /etc/hosts");
open(HOSTS, ">/etc/hosts") || bail ("Could not overwrite /etc/hosts: $!");
print HOSTS <<"ENDHOSTS";
# This file was created by $0
127.0.0.1       localhost
127.0.1.1       $fqdn $hostname

# The following lines are desirable for IPv6 capable hosts
::1     localhost ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
ENDHOSTS
close(HOSTS);
				    
print "Updating /etc/hostname...\n";
copy("/etc/hostname", "/etc/hostname.old") || bail("Could not copy /etc/hostname");
open(HOSTNAME, ">/etc/hostname") || bail ("Could not overwrite /etc/hostname: $!");
print HOSTNAME "$hostname\n";
close(HOSTNAME);

print "Setting hostname...\n";
system("/bin/hostname", $hostname);
print "\nDone!  You will need to reboot the workstation for the\n";
print "changes to take effect.\n";
confirm("Would you like to reboot now?") || bail("Please perform a full shutdown and reboot as soon as possible.");
print "The workstation will now power down completely.\n";
print "When you turn it back on, it will use the new IP address.\n\n";
print "(press ENTER to power down the workstation)";
getc(STDIN);
system("/sbin/poweroff");
exit 0;