{ config
, lib
, pkgs
, ...
}:

with lib;

let
  cfg = config.services.kea;

  xor = x: y: (!x && y) || (x && !y);
  format = pkgs.formats.json {};

  chooseNotNull = x: y: if x != null then x else y;

  ctrlAgentConfig = chooseNotNull cfg.ctrl-agent.configFile (format.generate "kea-ctrl-agent.conf" {
    Control-agent = cfg.ctrl-agent.settings;
  });

  dhcp4Config = chooseNotNull cfg.dhcp4.configFile (format.generate "kea-dhcp4.conf" {
    Dhcp4 = cfg.dhcp4.settings;
  });

  dhcp6Config = chooseNotNull cfg.dhcp6.configFile (format.generate "kea-dhcp6.conf" {
    Dhcp6 = cfg.dhcp6.settings;
  });

  dhcpDdnsConfig = chooseNotNull cfg.dhcp-ddns.configFile (format.generate "kea-dhcp-ddns.conf" {
    DhcpDdns = cfg.dhcp-ddns.settings;
  });

  package = pkgs.kea;
in
{
  options.services.kea = with types; {
    ctrl-agent = mkOption {
      description = lib.mdDoc ''
        Kea Control Agent configuration
      '';
      default = {};
      type = submodule {
        options = {
          enable = mkEnableOption (lib.mdDoc "Kea Control Agent");

          extraArgs = mkOption {
            type = listOf str;
            default = [];
            description = lib.mdDoc ''
              List of additional arguments to pass to the daemon.
            '';
          };

          configFile = mkOption {
            type = nullOr path;
            default = null;
            description = lib.mdDoc ''
              Kea Control Agent configuration as a path, see <https://kea.readthedocs.io/en/kea-${package.version}/arm/agent.html>.

              Takes preference over [settings](#opt-services.kea.ctrl-agent.settings).
              Most users should prefer using [settings](#opt-services.kea.ctrl-agent.settings) instead.
            '';
          };

          settings = mkOption {
            type = format.type;
            default = null;
            description = lib.mdDoc ''
              Kea Control Agent configuration as an attribute set, see <https://kea.readthedocs.io/en/kea-${package.version}/arm/agent.html>.
            '';
          };
        };
      };
    };

    dhcp4 = mkOption {
      description = lib.mdDoc ''
        DHCP4 Server configuration
      '';
      default = {};
      type = submodule {
        options = {
          enable = mkEnableOption (lib.mdDoc "Kea DHCP4 server");

          extraArgs = mkOption {
            type = listOf str;
            default = [];
            description = lib.mdDoc ''
              List of additional arguments to pass to the daemon.
            '';
          };

          configFile = mkOption {
            type = nullOr path;
            default = null;
            description = lib.mdDoc ''
              Kea DHCP4 configuration as a path, see <https://kea.readthedocs.io/en/kea-${package.version}/arm/dhcp4-srv.html>.

              Takes preference over [settings](#opt-services.kea.dhcp4.settings).
              Most users should prefer using [settings](#opt-services.kea.dhcp4.settings) instead.
            '';
          };

          settings = mkOption {
            type = format.type;
            default = null;
            example = {
              valid-lifetime = 4000;
              renew-timer = 1000;
              rebind-timer = 2000;
              interfaces-config = {
                interfaces = [
                  "eth0"
                ];
              };
              lease-database = {
                type = "memfile";
                persist = true;
                name = "/var/lib/kea/dhcp4.leases";
              };
              subnet4 = [ {
                subnet = "192.0.2.0/24";
                pools = [ {
                  pool = "192.0.2.100 - 192.0.2.240";
                } ];
              } ];
            };
            description = lib.mdDoc ''
              Kea DHCP4 configuration as an attribute set, see <https://kea.readthedocs.io/en/kea-${package.version}/arm/dhcp4-srv.html>.
            '';
          };
        };
      };
    };

    dhcp6 = mkOption {
      description = lib.mdDoc ''
        DHCP6 Server configuration
      '';
      default = {};
      type = submodule {
        options = {
          enable = mkEnableOption (lib.mdDoc "Kea DHCP6 server");

          extraArgs = mkOption {
            type = listOf str;
            default = [];
            description = lib.mdDoc ''
              List of additional arguments to pass to the daemon.
            '';
          };

          configFile = mkOption {
            type = nullOr path;
            default = null;
            description = lib.mdDoc ''
              Kea DHCP6 configuration as a path, see <https://kea.readthedocs.io/en/kea-${package.version}/arm/dhcp6-srv.html>.

              Takes preference over [settings](#opt-services.kea.dhcp6.settings).
              Most users should prefer using [settings](#opt-services.kea.dhcp6.settings) instead.
            '';
          };

          settings = mkOption {
            type = format.type;
            default = null;
            example = {
              valid-lifetime = 4000;
              renew-timer = 1000;
              rebind-timer = 2000;
              preferred-lifetime = 3000;
              interfaces-config = {
                interfaces = [
                  "eth0"
                ];
              };
              lease-database = {
                type = "memfile";
                persist = true;
                name = "/var/lib/kea/dhcp6.leases";
              };
              subnet6 = [ {
                subnet = "2001:db8:1::/64";
                pools = [ {
                  pool = "2001:db8:1::1-2001:db8:1::ffff";
                } ];
              } ];
            };
            description = lib.mdDoc ''
              Kea DHCP6 configuration as an attribute set, see <https://kea.readthedocs.io/en/kea-${package.version}/arm/dhcp6-srv.html>.
            '';
          };
        };
      };
    };

    dhcp-ddns = mkOption {
      description = lib.mdDoc ''
        Kea DHCP-DDNS configuration
      '';
      default = {};
      type = submodule {
        options = {
          enable = mkEnableOption (lib.mdDoc "Kea DDNS server");

          extraArgs = mkOption {
            type = listOf str;
            default = [];
            description = lib.mdDoc ''
              List of additional arguments to pass to the daemon.
            '';
          };

          configFile = mkOption {
            type = nullOr path;
            default = null;
            description = lib.mdDoc ''
              Kea DHCP-DDNS configuration as a path, see <https://kea.readthedocs.io/en/kea-${package.version}/arm/ddns.html>.

              Takes preference over [settings](#opt-services.kea.dhcp-ddns.settings).
              Most users should prefer using [settings](#opt-services.kea.dhcp-ddns.settings) instead.
            '';
          };

          settings = mkOption {
            type = format.type;
            default = null;
            example = {
              ip-address = "127.0.0.1";
              port = 53001;
              dns-server-timeout = 100;
              ncr-protocol = "UDP";
              ncr-format = "JSON";
              tsig-keys = [ ];
              forward-ddns = {
                ddns-domains = [ ];
              };
              reverse-ddns = {
                ddns-domains = [ ];
              };
            };
            description = lib.mdDoc ''
              Kea DHCP-DDNS configuration as an attribute set, see <https://kea.readthedocs.io/en/kea-${package.version}/arm/ddns.html>.
            '';
          };
        };
      };
    };
  };

  config = let
    commonServiceConfig = {
      ExecReload = "${pkgs.coreutils}/bin/kill -HUP $MAINPID";
      DynamicUser = true;
      User = "kea";
      ConfigurationDirectory = "kea";
      StateDirectory = "kea";
      UMask = "0077";
    };
  in mkIf (cfg.ctrl-agent.enable || cfg.dhcp4.enable || cfg.dhcp6.enable || cfg.dhcp-ddns.enable) (mkMerge [
  {
    environment.systemPackages = [ package ];
  }

  (mkIf cfg.ctrl-agent.enable {
    assertions = [{
        assertion = xor (cfg.ctrl-agent.settings == null) (cfg.ctrl-agent.configFile == null);
        message = "Either services.kea.ctrl-agent.settings or services.kea.ctrl-agent.configFile must be set to a non-null value.";
    }];

    environment.etc."kea/ctrl-agent.conf".source = ctrlAgentConfig;

    systemd.services.kea-ctrl-agent = {
      description = "Kea Control Agent";
      documentation = [
        "man:kea-ctrl-agent(8)"
        "https://kea.readthedocs.io/en/kea-${package.version}/arm/agent.html"
      ];

      after = [
        "network-online.target"
        "time-sync.target"
      ];
      wantedBy = [
        "kea-dhcp4-server.service"
        "kea-dhcp6-server.service"
        "kea-dhcp-ddns-server.service"
      ];

      environment = {
        KEA_PIDFILE_DIR = "/run/kea-ctrl-agent";
        KEA_LOCKFILE_DIR = "/run/kea-ctrl-agent";
      };

      restartTriggers = [
        ctrlAgentConfig
      ];

      serviceConfig = {
        ExecStart = "${package}/bin/kea-ctrl-agent -c /etc/kea/ctrl-agent.conf ${lib.escapeShellArgs cfg.ctrl-agent.extraArgs}";
        KillMode = "process";
        Restart = "on-failure";
        RuntimeDirectory = "kea-ctrl-agent";
      } // commonServiceConfig;
    };
  })

  (mkIf cfg.dhcp4.enable {
    assertions = [{
        assertion = xor (cfg.dhcp4.settings == null) (cfg.dhcp4.configFile == null);
        message = "Either services.kea.dhcp4.settings or services.kea.dhcp4.configFile must be set to a non-null value.";
    }];

    environment.etc."kea/dhcp4-server.conf".source = dhcp4Config;

    systemd.services.kea-dhcp4-server = {
      description = "Kea DHCP4 Server";
      documentation = [
        "man:kea-dhcp4(8)"
        "https://kea.readthedocs.io/en/kea-${package.version}/arm/dhcp4-srv.html"
      ];

      after = [
        "network-online.target"
        "time-sync.target"
      ];
      wantedBy = [
        "multi-user.target"
      ];

      environment = {
        KEA_PIDFILE_DIR = "/run/kea-dhcp4";
        KEA_LOCKFILE_DIR = "/run/kea-dhcp4";
      };

      restartTriggers = [
        dhcp4Config
      ];

      serviceConfig = {
        ExecStart = "${package}/bin/kea-dhcp4 -c /etc/kea/dhcp4-server.conf ${lib.escapeShellArgs cfg.dhcp4.extraArgs}";
        # Kea does not request capabilities by itself
        AmbientCapabilities = [
          "CAP_NET_BIND_SERVICE"
          "CAP_NET_RAW"
        ];
        CapabilityBoundingSet = [
          "CAP_NET_BIND_SERVICE"
          "CAP_NET_RAW"
        ];
        RuntimeDirectory = "kea-dhcp4";
      } // commonServiceConfig;
    };
  })

  (mkIf cfg.dhcp6.enable {
    assertions = [{
        assertion = xor (cfg.dhcp6.settings == null) (cfg.dhcp6.configFile == null);
        message = "Either services.kea.dhcp6.settings or services.kea.dhcp6.configFile must be set to a non-null value.";
    }];

    environment.etc."kea/dhcp6-server.conf".source = dhcp6Config;

    systemd.services.kea-dhcp6-server = {
      description = "Kea DHCP6 Server";
      documentation = [
        "man:kea-dhcp6(8)"
        "https://kea.readthedocs.io/en/kea-${package.version}/arm/dhcp6-srv.html"
      ];

      after = [
        "network-online.target"
        "time-sync.target"
      ];
      wantedBy = [
        "multi-user.target"
      ];

      environment = {
        KEA_PIDFILE_DIR = "/run/kea-dhcp6";
        KEA_LOCKFILE_DIR = "/run/kea-dhcp6";
      };

      restartTriggers = [
        dhcp6Config
      ];

      serviceConfig = {
        ExecStart = "${package}/bin/kea-dhcp6 -c /etc/kea/dhcp6-server.conf ${lib.escapeShellArgs cfg.dhcp6.extraArgs}";
        # Kea does not request capabilities by itself
        AmbientCapabilities = [
          "CAP_NET_BIND_SERVICE"
        ];
        CapabilityBoundingSet = [
          "CAP_NET_BIND_SERVICE"
        ];
        RuntimeDirectory = "kea-dhcp6";
      } // commonServiceConfig;
    };
  })

  (mkIf cfg.dhcp-ddns.enable {
    assertions = [{
        assertion = xor (cfg.dhcp-ddns.settings == null) (cfg.dhcp-ddns.configFile == null);
        message = "Either services.kea.dhcp-ddns.settings or services.kea.dhcp-ddns.configFile must be set to a non-null value.";
    }];

    environment.etc."kea/dhcp-ddns.conf".source = dhcpDdnsConfig;

    systemd.services.kea-dhcp-ddns-server = {
      description = "Kea DHCP-DDNS Server";
      documentation = [
        "man:kea-dhcp-ddns(8)"
        "https://kea.readthedocs.io/en/kea-${package.version}/arm/ddns.html"
      ];

      after = [
        "network-online.target"
        "time-sync.target"
      ];
      wantedBy = [
        "multi-user.target"
      ];

      environment = {
        KEA_PIDFILE_DIR = "/run/kea-dhcp-ddns";
        KEA_LOCKFILE_DIR = "/run/kea-dhcp-ddns";
      };

      restartTriggers = [
        dhcpDdnsConfig
      ];

      serviceConfig = {
        ExecStart = "${package}/bin/kea-dhcp-ddns -c /etc/kea/dhcp-ddns.conf ${lib.escapeShellArgs cfg.dhcp-ddns.extraArgs}";
        AmbientCapabilities = [
          "CAP_NET_BIND_SERVICE"
        ];
        CapabilityBoundingSet = [
          "CAP_NET_BIND_SERVICE"
        ];
        RuntimeDirectory = "kea-dhcp-ddns";
      } // commonServiceConfig;
    };
  })

  ]);

  meta.maintainers = with maintainers; [ hexa ];
  # uses attributes of the linked package
  meta.buildDocsInSandbox = false;
}