{ flake, config, pkgs, lib, ... }:
{
  config = {
    services.kea = {
      dhcp4 = {
        enable = true;
        settings = {
          valid-lifetime = 4000;
          rebind-timer = 2000;
          renew-timer = 1000;

          interfaces-config = {
            interfaces = [ "lan" "mgmt" ];
          };

          lease-database = {
            name = "/var/lib/kea/dhcp4.leases";
            persist = true;
            type = "memfile";
          };

          client-classes = [
            { name = "ipxe";
              test = "option[77].hex == 'iPXE'";
              next-server = "10.141.0.1";
              boot-file-name = "netboot.ipxe";
              only-if-required = true;
            }
            { name = "uefi-64";
              test = "substring(option[60].hex,0,20) == 'PXEClient:Arch:00007' or substring(option[60].hex,0,20) == 'PXEClient:Arch:00008' or substring(option[60].hex,0,20) == 'PXEClient:Arch:00009'";
              only-if-required = true;
              option-data = [
                { name = "tftp-server-name"; data = "10.141.0.1"; }
              ];
              boot-file-name = "ipxe.efi";
            }
            { name = "uefi-32";
              test = "substring(option[60].hex,0,20) == 'PXEClient:Arch:00002' or substring(option[60].hex,0,20) == 'PXEClient:Arch:00006'";
              only-if-required = true;
              option-data = [
                { name = "tftp-server-name"; data = "10.141.0.1"; }
              ];
              boot-file-name = "i386-ipxe.efi";
            }
            { name = "legacy";
              test = "substring(option[60].hex,0,20) == 'PXEClient:Arch:00000'";
              only-if-required = true;
              option-data = [
                { name = "tftp-server-name"; data = "10.141.0.1"; }
              ];
              boot-file-name = "undionly.kpxe";
            }
          ];

          dhcp-ddns.enable-updates = true;
          ddns-send-updates = false;
          ddns-override-client-update = true;
          ddns-override-no-update = true;
          ddns-replace-client-name = "when-not-present";
          ddns-generated-prefix = "noname";
          ddns-update-on-renew = true;

          subnet4 = [
            { subnet = "10.141.0.0/24";
              option-data = [
                { name = "domain-name-servers";
                  data = "10.141.0.1";
                }
                { name = "broadcast-address";
                  data = "10.141.0.255";
                }
                { name = "routers";
                  data = "10.141.0.1";
                }
                { name = "domain-name";
                  data = "yggdrasil";
                }
                { name = "domain-search";
                  data = "lan.yggdrasil, yggdrasil";
                }
              ];
              ddns-send-updates = true;
              ddns-qualifying-suffix = "lan.yggdrasil";
              pools = [ { pool = "10.141.0.128 - 10.141.0.254"; } ];
              require-client-classes = ["ipxe" "uefi-64" "uefi-32" "legacy"];
              reservations = [
                { hostname = "sif";
                  hw-address = "3c:e1:a1:52:24:35";
                }
                { hostname = "sif";
                  hw-address = "ee:32:68:76:83:ac";
                }
                { hostname = "sif";
                  hw-address = "48:2a:e3:64:62:97";
                }
                { hostname = "eos";
                  hw-address = "00:d8:61:79:c5:40";
                }
              ];
            }
            { subnet = "10.141.1.0/24";
              option-data = [
                { name = "domain-name-servers";
                  data = "10.141.1.1";
                }
                { name = "broadcast-address";
                  data = "10.141.1.255";
                }
                { name = "domain-name";
                  data = "yggdrasil";
                }
                { name = "domain-search";
                  data = "mgmt.yggdrasil, yggdrasil";
                }
              ];
              ddns-send-updates = true;
              ddns-qualifying-suffix = "mgmt.yggdrasil";
              pools = [ { pool = "10.141.1.128 - 10.141.1.254"; } ];
              reservations = [
                { hostname = "switch01";
                  hw-address = "60:a4:b7:53:94:b5";
                  ip-address = "10.141.1.2";
                }
                { hostname = "ap01";
                  hw-address = "74:ac:b9:29:ad:9a";
                  ip-address = "10.141.1.4";
                }
              ];
            }
            { subnet = "10.141.2.0/24";
              option-data = [
                { name = "domain-name-servers";
                  data = "10.141.2.1";
                }
                { name = "broadcast-address";
                  data = "10.141.2.255";
                }
                { name = "routers";
                  data = "10.141.2.1";
                }
              ];
              ddns-send-updates = false;
              pools = [ { pool = "10.141.2.128 - 10.141.2.254"; } ];
              reservations = [];
            }
          ]; 
        };
      };
      dhcp6 = {
        enable = true;
        settings = {
          interfaces-config = {
            interfaces = [ "lan" ];
          };

          lease-database = {
            name = "/var/lib/kea/dhcp6.leases";
            persist = true;
            type = "memfile";
          };
        };
      };
      dhcp-ddns = {
        enable = true;
        settings = {
          forward-ddns = {
            ddns-domains = [
              { name = "lan.yggdrasil.";
                dns-servers = [
                  { ip-address = "127.0.0.1";
                    port = 5353;
                    key-name = "local_key";
                  }
                ];
              }
              { name = "mgmt.yggdrasil.";
                dns-servers = [
                  { ip-address = "127.0.0.1";
                    port = 5353;
                    key-name = "local_key";
                  }
                ];
              }
            ];
          };
          reverse-ddns = {
            ddns-domains = [
              { name = "0.141.10.in-addr.arpa.";
                dns-servers = [
                  { ip-address = "127.0.0.1";
                    port = 5353;
                    key-name = "local_key";
                  }
                ];
              }
              { name = "1.141.10.in-addr.arpa.";
                dns-servers = [
                  { ip-address = "127.0.0.1";
                    port = 5353;
                    key-name = "local_key";
                  }
                ];
              }
            ];
          };
        };
      };
    };

    systemd.services.kea-dhcp-ddns-server = {
      preStart = let 
        configLines = [
          "<?include \"\${CREDENTIALS_DIRECTORY}/knot-tsig.json.frag\"?>"
        ] ++ lib.mapAttrsToList (k: v:
          "\"${k}\": ${builtins.toJSON v}"
        ) config.services.kea.dhcp-ddns.settings;

        config-template = pkgs.writeText "dhcp-ddns.conf" ''
          {"DhcpDdns": {
            ${lib.concatStringsSep ",\n  " configLines}
          }}
        '';
      in ''
        ${pkgs.envsubst}/bin/envsubst -i "${config-template}" -o "''${RUNTIME_DIRECTORY}/dhcp-ddns.conf"
      '';

      serviceConfig = {
        ExecStart = lib.mkForce ''
          ${pkgs.kea}/bin/kea-dhcp-ddns -c "''${RUNTIME_DIRECTORY}/dhcp-ddns.conf" ${lib.escapeShellArgs config.services.kea.dhcp-ddns.extraArgs}
        '';
        LoadCredential = [
          "knot-tsig.json.frag:${config.sops.secrets."kea-knot-tsig.json.frag".path}"
        ];
      };
    };

    sops.secrets."kea-knot-tsig.json.frag" = {
      format = "binary";
      sopsFile = ./knot-tsig.json.frag;
    };

    systemd.services."installer-atftpd" = {
      description = "TFTP Server for PXE Booting NixOS Installer";
      after = [ "network.target" ];
      wantedBy = [ "multi-user.target" ];
      serviceConfig.ExecStart = let
        installerBuild = flake.nixosConfigurations.installer-x86_64-linux-netboot.config.system.build;
        ipxe = pkgs.ipxe.override {
          additionalTargets = {
            "bin-i386-efi/ipxe.efi" = "i386-ipxe.efi";
          };
        };
        tftpRoot = pkgs.runCommandLocal "installer-netboot" {} ''
          mkdir -p $out
          install -m 0444 -t $out \
            ${installerBuild.netbootRamdisk}/initrd \
            ${installerBuild.kernel}/bzImage \
            ${installerBuild.netbootIpxeScript}/netboot.ipxe \
            ${ipxe}/ipxe.efi ${ipxe}/i386-ipxe.efi ${ipxe}/undionly.kpxe
        '';
      in "${pkgs.atftp}/sbin/atftpd --daemon --no-fork --bind-address=10.141.0.1 ${tftpRoot}";
    };
  };
}