#
# RouterOS script: dhcp-to-dns
# Copyright (c) 2013-2018 Christian Hesse <mail@eworm.de>
#
# check DHCP leases and add/remove/update DNS entries

:global "identity";
:global "domain";
:global "hostname-in-zone";

:local zone;
:if ($"hostname-in-zone" = true) do={
  :set zone ("dhcp." . $identity . "." . $domain);
} else={
  :set zone ("dhcp." . $domain);
}
:local ttl "00:05:00";
:local hostname;
:local fqdn;
:local dnsip;
:local dhcpip;
:local dnsnode;
:local dhcpnode;

:foreach static in=[ / ip dns static find where name ~ (".*\\." . $zone) ] do={
  :set fqdn [ / ip dns static get $static name ];
  :set hostname [ :pick $fqdn 0 ( [ :len $fqdn ] - ( [ :len $zone ] + 1 ) ) ];
  :set dhcpnode [ / ip dhcp-server lease find where host-name=$hostname dynamic=yes ];
  :if ( [ :len $dhcpnode ] > 0) do={
    :log debug ("Lease for " . $hostname . " still exists. Not deleting.");
  } else={
    :local found false;
    :log info ("Lease expired for " . $hostname . ", deleting DNS entry.");
    / ip dns static remove $static;
  }
}

:foreach lease in=[ / ip dhcp-server lease find where dynamic=yes ] do={
  :local mac [ / ip dhcp-server lease get $lease mac-address ];
  :set dhcpip [ / ip dhcp-server lease get $lease address ];
  :local comment ("managed by dhcp-to-dns for " . $mac);
  :set hostname [ / ip dhcp-server lease get $lease host-name ];

  :while ($hostname ~ " ") do={
    :local pos [ :find $hostname " " ];
    :set hostname ( [ :pick $hostname 0 $pos ] . [ :pick $hostname ($pos + 1) 999 ] );
  };

  :if ( [ :len $hostname ] > 0) do={
    :set fqdn ( $hostname . "." . $zone );
    :set dnsnode [ / ip dns static find where name=$fqdn ];
    :if ( [ :len $dnsnode ] > 0 ) do={
      :set dnsip [ / ip dns static get $dnsnode address ];

      :local leases [ / ip dhcp-server lease find where host-name=$hostname dynamic=yes ];
      :local hostnamecount [ :len [ / ip dhcp-server lease find where host-name=$hostname dynamic=yes ] ];
      :if ( $hostnamecount > 1) do={
        :foreach j,lease in=$leases do={
          :if ($j + 1 = $hostnamecount) do={
            :set dhcpip [ / ip dhcp-server lease get $lease address ];
          }
        }
      }

      :if ( $dnsip = $dhcpip ) do={
        :log debug ("DNS entry for " . $fqdn . " does not need updating.");
      } else={
        :log info ("Replacing DNS entry for " . $fqdn . ", new address is " . $dhcpip . ".");
        / ip dns static set name=$fqdn address=$dhcpip ttl=$ttl comment=$comment $dnsnode;
      }
    } else={
      :log info ("Adding new DNS entry for " . $fqdn . ", address is " . $dhcpip . ".");
      / ip dns static add name=$fqdn address=$dhcpip ttl=$ttl comment=$comment;
    }
  }
}