use strict;
use warnings;

my @data = (
    ['app12', 'eth1', 'static', '192.168.0.5', '255.255.255.0', '192.168.0.1'],
    ['app15', 'eth0', 'dhcp',   '',            '',              ''],
    ['app15', 'eth1', 'static', '192.168.0.4', '255.255.255.0', '192.168.0.1'],
    ['app17', 'eth1', 'static', '192.168.0.2', '255.255.255.0', '192.168.0.1'],
);

my %hosts;

while (my @row = @{shift @data || []}) {
    push @{$hosts{$row[0]}}, \@row;
}

for my $host (keys %hosts) {
    genFile ($host, $hosts{$host});
}


sub genFile {
    my ($host, $rows) = @_;
    my $fileName = "/tmp/interfaces.$host";
    my @ifaces   = map {$_->[1]} @$rows;

    print "--------- $fileName --------------\n";
    print <<STR;
auto lo
iface lo inet loopback

auto @ifaces
STR

    for my $row (@$rows) {
        my ($hostname, $iface, $type, $address, $netmask, $gateway) = @$row;

        if ($type eq "dhcp") {
            print "\niface $iface inet $type\n";
        } else {
            print <<STR;

iface $iface inet $type
address $address
netmask $netmask
network 192.168.0.0
broadcast 192.168.0.255
gateway $gateway
STR
        }
    }
}

##</code><code>##

--------- /tmp/interfaces.app15 --------------
auto lo
iface lo inet loopback

auto eth0 eth1

iface eth0 inet dhcp

iface eth1 inet static
address 192.168.0.4
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
gateway 192.168.0.1
--------- /tmp/interfaces.app12 --------------
auto lo
iface lo inet loopback

auto eth1

iface eth1 inet static
address 192.168.0.5
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
gateway 192.168.0.1
--------- /tmp/interfaces.app17 --------------
auto lo
iface lo inet loopback

auto eth1

iface eth1 inet static
address 192.168.0.2
netmask 255.255.255.0
network 192.168.0.0
broadcast 192.168.0.255
gateway 192.168.0.1

##</code><code>##

my @hostRows;

while ((my @row = @{shift @data || []}) || @hostRows) {
    if (@hostRows && (! @row || $row[0] ne $hostRows[0][0])) {
        genFile ($hostRows[0][0], \@hostRows);
        @hostRows = ();
        next if ! @row;
    }

    push @hostRows, \@row;
}