#!rsc
# RouterOS script: dhcp-to-dns
# Copyright (c) 2013-2019 Christian Hesse <mail@eworm.de>
#
# check DHCP leases and add/remove/update DNS entries

:global Identity;
:global Domain;
:global HostNameInZone;

:local Zone;
:if ($HostNameInZone = true) do={
  :set Zone ("dhcp." . $Identity . "." . $Domain);
} else={
  :set Zone ("dhcp." . $Domain);
}
:local Ttl 5m;
: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=$HostName dynamic=yes ];
      :local HostNameCount [ / ip dhcp-server lease print count-only where host-name=$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;
    }
  }
}