{ lib, pkgs, config, ... }:
let
  cfg = config.skynet_dns;

  # reads that date to a string (will need to be fixed in 2038)
  current_date = toString builtins.currentTime;

  # base config for domains we own (skynet.ie, csn.ul.ie, ulcompsoc.ie)
  get_config_file = (domain:
    ''
    $TTL 60  ; 1 minute
    ; hostmaster@${domain} is an email address that recieves stuff related to dns
    @ IN SOA ${cfg.own.nameserver}.${domain}. hostmaster.${domain}. (
       ; Serial (YYYYMMDDCC) this has to be updated for each time the record is updated
       ${current_date}
       600        ; Refresh (10 minutes)
       300        ; Retry   (5 minutes)
       604800     ; Expire  (1 week)
       3600       ; Minimum (1 hour)
      )

    @ NS  ns1.${domain}.
    @ NS  ns2.${domain}.
      ; @ stands for teh root domain so teh A record below is where ${domain} points to
    ;@ A   193.1.99.76
    ;@ MX  5 ${domain}.

    ; can have multiple mailserves
    ;@ MX  20 mail2.${domain}.


    ; ------------------------------------------
    ; Server Names
    ; ------------------------------------------

    ; External addresses
    ; ------------------------------------------
    ${lib.strings.concatMapStrings (x: x + "\n") cfg.records.external}


    ; this is fixed for now
    wintermute      A       193.1.101.148


    ; internal addresses
    ; ------------------------------------------
    ; May come back to this idea in teh future
    ; agentjones.int  A       172.20.20.1


    ; cname's
    ; ------------------------------------------
    ${lib.strings.concatMapStrings (x: x + "\n") cfg.records.cname}

    ''
  );


    # https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/4/html/reference_guide/s2-bind-configuration-zone-reverse
    # config for our reverse dnspointers (not properly working)
    get_config_file_rev = (domain:
      ''
      $ORIGIN 99.1.193.in-addr.arpa.
      $TTL 60  ; 1 minute
      ; hostmaster@${domain} is an email address that recieves stuff related to dns
      @ IN SOA ${cfg.own.nameserver}.${domain}. hostmaster.${domain}. (
         ; Serial (YYYYMMDDCC) this has to be updated for each time the record is updated
         ${current_date}
         600        ; Refresh (10 minutes)
         300        ; Retry   (5 minutes)
         604800     ; Expire  (1 week)
         3600       ; Minimum (1 hour)
        )

      @ NS  ns1.${domain}.
      @ NS  ns2.${domain}.

      ${lib.strings.concatMapStrings (x: x + "." + domain + ".\n") cfg.records.reverse}
      ''
    );

    # domains we dont have proper ownship over, only here to ensure the logs dont get cluttered.
    get_config_file_old_domains = (domain:
      ''
      $TTL 60  ; 1 minute
      ; hostmaster@skynet.ie is an email address that recieves stuff related to dns
      @ IN SOA ${cfg.own.nameserver}.skynet.ie. hostmaster.skynet.ie. (
         ; Serial (YYYYMMDDCC) this has to be updated for each time the record is updated
         ${current_date}
         600        ; Refresh (10 minutes)
         300        ; Retry   (5 minutes)
         604800     ; Expire  (1 week)
         3600       ; Minimum (1 hour)
        )

      @ NS  ns1.skynet.ie.
      @ NS  ns2.skynet.ie.

      ''
    );

  # arrys  of teh two nameservers
  tmp1 = ["193.1.99.109"];
  tmp2 = ["193.1.99.120"];

  primaries = (if cfg.primary then
    # primary servers have no primaries (ones they listen to)
    []
  else
    if builtins.elem cfg.own.ip tmp1 then
      tmp2
    else
      tmp1
  );

  secondaries = (if cfg.primary then
      if builtins.elem cfg.own.ip tmp1 then
        tmp2
      else
        tmp1
    else
      []
  );

  # small function to tidy up the spam of the cache networks, would use teh subnet except all external traffic has the ip of teh router
  create_cache_networks = (map (x: "193.1.99.${toString x}/32" ) (lib.lists.range 71 126) );


 # standard function to create the etc file, pass in the text and domain and it makes it
  create_entry_etc_sub = domain: text:  {
    # Creates /etc/skynet/dns/domain
    "skynet/dns/${domain}" = {
      user = "named";
      group = "named";

      # The UNIX file mode bits
      mode = "0664";

      text = text;
    };
  };
# (text.owned "csn.ul.ie")


  # standard function to create the etc file, pass in the text and domain and it makes it
  create_entry_etc = domain: type:
    if type == "owned" then
      create_entry_etc_sub domain (text.owned domain)
    else if type == "reverse" then
      create_entry_etc_sub domain (text.reverse domain)
    else if type == "old" then
      create_entry_etc_sub domain (text.old domain)
    else
      {};

  create_entry_zone = (domain: extraConfig: {
     "${domain}" = {
       extraConfig = ''
         ${extraConfig}
         // for bumping the config
         // ${current_date}
         '';
       # really wish teh nixos config didnt use master/slave
       master = cfg.primary;
       masters = primaries;
       slaves = secondaries;
       # need to write this to a file
       # using the date in it so it will trigger a restart
       file = "/etc/skynet/dns/${domain}";
       # no leading whitespace for first line
     };
  });

  text = {
    owned = domain: get_config_file domain;
    reverse = domain: get_config_file_rev domain;
    old = domain: get_config_file_old_domains domain;
  };

  extraConfig = {
    owned =
      if cfg.primary then
        ''
        allow-update { key rfc2136key.skynet.ie.; };

        dnssec-policy default;
        inline-signing yes;
        ''
      else
        "";

    # no extra config for reverse
    reverse = "";

    old = "";
  };

in {

  imports = [
    ../applications/firewall.nix
  ];

  options = {
    skynet_dns = {
      enable = lib.mkEnableOption {
        default = false;
        example = true;
        description = "Skynet DNS";
        type = lib.types.bool;
      };

      primary = lib.mkOption {
        type = lib.types.bool;
        default = false;
      };

      own = {
        ip = lib.mkOption {
          type = lib.types.str;
          description = ''
            ip of this server
          '';
        };

        nameserver = lib.mkOption {
          default = "ns1";
          type = lib.types.str;
          description = ''
            the hostname of this nameserver, eg ns1, ns2
          '';
        };

        external = lib.mkOption {
          default = [ ];
          type = lib.types.listOf lib.types.str;
          description = ''
            External records like: agentjones      A       193.1.99.72
          '';
        };

        cname = lib.mkOption {
          default = [ ];
          type = lib.types.listOf lib.types.str;
          description = ''
            External records like: ns1             CNAME   ns1
          '';
        };

        reverse = lib.mkOption {
          default = [ ];
          type = lib.types.listOf lib.types.str;
          description = ''
            External records like: 20    IN     PTR    vigil
          '';
        };
      };


      records = {
        external = lib.mkOption {
          default = [ ];
          type = lib.types.listOf lib.types.str;
          description = ''
            External records like: agentjones      A       193.1.99.72
          '';
        };

        cname = lib.mkOption {
          default = [ ];
          type = lib.types.listOf lib.types.str;
          description = ''
            External records like: ns1             CNAME   ns1
          '';
        };

        reverse = lib.mkOption {
          default = [ ];
          type = lib.types.listOf lib.types.str;
          description = ''
            External records like: 20    IN     PTR    vigil
          '';
        };
      };

    };
  };

  config = lib.mkIf cfg.enable {

    # open the firewall for this
    skynet_firewall.forward = [
      "ip daddr ${cfg.own.ip} tcp dport 53 counter packets 0 bytes 0 accept"
      "ip daddr ${cfg.own.ip} udp dport 53 counter packets 0 bytes 0 accept"
    ];

    services.bind.zones =
      (create_entry_zone "csn.ul.ie" extraConfig.owned ) //
      (create_entry_zone "skynet.ie" extraConfig.owned ) //
      (create_entry_zone "ulcompsoc.ie" extraConfig.owned ) //

      (create_entry_zone "99.1.193.in-addr.arpa" extraConfig.reverse )//

      (create_entry_zone "conradcollins.net" extraConfig.old )//
      (create_entry_zone "edelharty.net" extraConfig.old );

    environment.etc =
      (create_entry_etc "csn.ul.ie" "owned") //
      (create_entry_etc "skynet.ie" "owned") //
      (create_entry_etc "ulcompsoc.ie" "owned") //

      (create_entry_etc "99.1.193.in-addr.arpa" "reverse") //

      (create_entry_etc "conradcollins.net" "old") //
      (create_entry_etc "edelharty.net" "old");


    # secrets required
    age.secrets.dns_dnskeys = {
      file = ../secrets/dns_dnskeys.conf.age;
      owner = "named";
      group = "named";
    };

    networking.firewall = {
      allowedTCPPorts = [53];
      allowedUDPPorts = [53];
    };

    services.bind = {
      enable = true;

      ipv4Only = true;

      # need to take a look at https://nixos.org/manual/nixos/unstable/#module-security-acme-config-dns
      extraConfig = ''
        include "/run/agenix/dns_dnskeys";
      '';

      # piles of no valid RRSIG resolving 'com/DS/IN' errors
      extraOptions = ''
        dnssec-validation yes;
      '';

      # set the upstream dns servers
      # overrides the default dns servers
      forwarders = [
        # Cloudflare
        "1.1.1.1"
        # Google
        "8.8.8.8"
        # Quad9
        "9.9.9.9"
      ];

      cacheNetworks  = [
        # this server itself
        "127.0.0.0/24"
        # all of skynet can use this as a resolver
        /*
        Origianl idea, however all external traffic had the ip of the router
        "193.1.99.64/26"

        So to fix this we need to allow smaller ranges? - Didnt work
        Fallback is explisitly listing each ip we have

        Now have a function for it
        */
     ] ++ create_cache_networks;
    };

    # creates a folder in /etc for the dns to use
    users.users.named = {
      createHome = true;
      home = "/etc/skynet/dns";
    };

  };
}