{ config, pkgs, ... }:

{
  #
  # iptables
  #
  networking.firewall.enable = false;
  system.activationScripts.iptables =
    let
      log = false;
      when = c: f: if c then f else "";
    in
      ''
        ip4tables() { ${pkgs.iptables}/sbin/iptables "$@"; }
        ip6tables() { ${pkgs.iptables}/sbin/ip6tables "$@"; }
        ipXtables() { ip4tables "$@"; ip6tables "$@"; }

        #
        # nat
        #

        # reset tables
        ipXtables -t nat -F
        ipXtables -t nat -X

        #
        ipXtables -t nat -A PREROUTING -j REDIRECT ! -i retiolum -p tcp --dport ssh --to-ports 0
        ipXtables -t nat -A PREROUTING -j REDIRECT -p tcp --dport 11423 --to-ports ssh

        #
        # filter
        #

        # reset tables
        ipXtables -P INPUT DROP
        ipXtables -P FORWARD DROP
        ipXtables -F
        ipXtables -X

        # create custom chains
        ipXtables -N Retiolum

        # INPUT
        ipXtables -A INPUT -j ACCEPT -m conntrack --ctstate RELATED,ESTABLISHED
        ipXtables -A INPUT -j ACCEPT -i lo
        ipXtables -A INPUT -j ACCEPT -p tcp --dport ssh -m conntrack --ctstate NEW
        ipXtables -A INPUT -j ACCEPT -p tcp --dport http -m conntrack --ctstate NEW
        ipXtables -A INPUT -j ACCEPT -p tcp --dport tinc -m conntrack --ctstate NEW
        ipXtables -A INPUT -j ACCEPT -p tcp --dport smtp -m conntrack --ctstate NEW
        ipXtables -A INPUT -j Retiolum -i retiolum
        ${when log "ipXtables -A INPUT -j LOG --log-level info --log-prefix 'INPUT DROP '"}

        # FORWARD
        ${when log "ipXtables -A FORWARD -j LOG --log-level info --log-prefix 'FORWARD DROP '"}

        # Retiolum
        ip4tables -A Retiolum -j ACCEPT -p icmp --icmp-type echo-request
        ip6tables -A Retiolum -j ACCEPT -p ipv6-icmp -m icmp6 --icmpv6-type echo-request


        ${when log "ipXtables -A Retiolum -j LOG --log-level info --log-prefix 'REJECT '"}
        ipXtables -A Retiolum -j REJECT -p tcp --reject-with tcp-reset
        ip4tables -A Retiolum -j REJECT -p udp --reject-with icmp-port-unreachable
        ip4tables -A Retiolum -j REJECT        --reject-with icmp-proto-unreachable
        ip6tables -A Retiolum -j REJECT -p udp --reject-with icmp6-port-unreachable
        ip6tables -A Retiolum -j REJECT

      '';
}