{ config, lib, pkgs, ... }: let
  cfg = config.lass.sync-containers3;
  slib = pkgs.stockholm.lib;
in {
  options.lass.sync-containers3 = {
    inContainer = {
      enable = lib.mkEnableOption "container config for syncing";
      pubkey = lib.mkOption {
        type = lib.types.str; # TODO ssh key
      };
    };
    containers = lib.mkOption {
      default = {};
      type = lib.types.attrsOf (lib.types.submodule ({ config, ... }: {
        options = {
          name = lib.mkOption {
            type = lib.types.str;
            default = config._module.args.name;
          };
          sshKey = lib.mkOption {
            type = slib.types.absolute-pathname;
          };
          luksKey = lib.mkOption {
            type = slib.types.absolute-pathname;
            default = config.sshKey;
          };
          ephemeral = lib.mkOption {
            type = lib.types.bool;
            default = false;
          };
        };
      }));
    };
  };
  config = lib.mkMerge [
    (lib.mkIf (cfg.containers != {}) {

      containers = lib.mapAttrs' (n: ctr: lib.nameValuePair ctr.name {
        config = {
          environment.systemPackages = [
            pkgs.dhcpcd
            pkgs.git
            pkgs.jq
          ];
          networking.useDHCP = lib.mkForce true;
          systemd.services.autoswitch = {
            environment = {
              NIX_REMOTE = "daemon";
            };
            wantedBy = [ "multi-user.target" ];
            serviceConfig.ExecStart = pkgs.writers.writeDash "autoswitch" ''
              set -efu
              ln -frs /var/state/var_src /var/src
              if test -e /var/src/nixos-config; then
                /run/current-system/sw/bin/nixos-rebuild -I /var/src switch || :
              fi
            '';
            unitConfig.X-StopOnRemoval = false;
          };
        };
        autoStart = false;
        enableTun = true;
        ephemeral = ctr.ephemeral;
        privateNetwork = true;
        hostBridge = "ctr0";
        bindMounts = {
          "/etc/resolv.conf".hostPath = "/etc/resolv.conf";
          "/var/lib/self/disk" = {
            hostPath = "/var/lib/sync-containers3/${ctr.name}/disk";
            isReadOnly = false;
          };
          "/var/state" = {
            hostPath = "/var/lib/sync-containers3/${ctr.name}/state";
            isReadOnly = false;
          };
        };
      }) cfg.containers;

      systemd.services = lib.foldr lib.recursiveUpdate {} (lib.flatten (map (ctr: [
        { "${ctr.name}_syncer" = {
          path = with pkgs; [
            coreutils
            consul
            rsync
            openssh
            systemd
          ];
          startAt = "*:0/1";
          serviceConfig = {
            User = "${ctr.name}_container";
            LoadCredential = [
              "ssh_key:${ctr.sshKey}"
            ];
            ExecCondition = pkgs.writers.writeDash "${ctr.name}_checker" ''
              set -efu
              ! systemctl is-active --quiet container@${ctr.name}.service
            '';
            ExecStart = pkgs.writers.writeDash "${ctr.name}_syncer" ''
              set -efux
              consul lock sync_${ctr.name} ${pkgs.writers.writeDash "${ctr.name}-sync" ''
                set -efux
                if /run/wrappers/bin/ping -c 1 ${ctr.name}.r; then
                  touch "$HOME"/incomplete
                  rsync -a -e "ssh -i $CREDENTIALS_DIRECTORY/ssh_key" --inplace container_sync@${ctr.name}.r:disk "$HOME"/disk
                  rm "$HOME"/incomplete
                fi
              ''}
            '';
          };
        }; }
        { "${ctr.name}_watcher" = {
          path = with pkgs; [
            coreutils
            consul
            cryptsetup
            curl
            mount
            util-linux
            jq
          ];
          serviceConfig = {
            ExecStart = pkgs.writers.writeDash "${ctr.name}_watcher" ''
              set -efux
              while sleep 5; do
                # get the payload
                # check if the host reacted recently
                case $(curl -s -o /dev/null --retry 10 -w '%{http_code}' http://127.0.0.1:8500/v1/kv/containers/${ctr.name}) in
                  404)
                    echo 'got 404 from kv, should kill the container'
                    break
                    ;;
                  500)
                    echo 'got 500 from kv, will kill container'
                    break
                    ;;
                  200)
                    # echo 'got 200 from kv, will check payload'
                    export payload=$(consul kv get containers/${ctr.name})
                    if [ "$(jq -rn 'env.payload | fromjson.host')" = '${config.networking.hostName}' ]; then
                      # echo 'we are the host, continuing'
                      continue
                    else
                      echo 'we are not host, killing container'
                      break
                    fi
                    ;;
                  *)
                    echo 'unknown state, continuing'
                    continue
                    ;;
                esac
              done
              /run/current-system/sw/bin/nixos-container stop ${ctr.name} || :
              umount /var/lib/sync-containers3/${ctr.name}/state || :
              cryptsetup luksClose ${ctr.name} || :
            '';
          };
        }; }
        { "${ctr.name}_scheduler" = {
          wantedBy = [ "multi-user.target" ];
          path = with pkgs; [
            coreutils
            consul
            cryptsetup
            mount
            util-linux
            curl
            systemd
            jq
            retry
            bc
          ];
          serviceConfig = {
            Restart = "always";
            RestartSec = "30s";
            ExecStart = pkgs.writers.writeDash "${ctr.name}_scheduler" ''
              set -efux
              # get the payload
              # check if the host reacted recently
              case $(curl -s -o /dev/null --retry 10 -w '%{http_code}' http://127.0.0.1:8500/v1/kv/containers/${ctr.name}) in
                404)
                  # echo 'got 404 from kv, will create container'
                  ;;
                500)
                  # echo 'got 500 from kv, retrying again'
                  exit 0
                  ;;
                200)
                  # echo 'got 200 from kv, will check payload'
                  export payload=$(consul kv get containers/${ctr.name})
                  if [ "$(jq -rn 'env.payload | fromjson.host')" = '${config.networking.hostName}' ]; then
                    echo 'we are the host, starting container'
                  else
                    # echo 'we are not host, checking timestamp'
                    # if [ $(echo "$(date +%s) - $(jq -rn 'env.payload | fromjson.time') > 100" | bc) -eq 1 ]; then
                    if [ "$(jq -rn 'env.payload | fromjson.time | now - tonumber > 100')" = 'true' ]; then
                      echo 'last beacon is more than 100s ago, taking over'
                    else
                      # echo 'last beacon was recent. trying again'
                      exit 0
                    fi
                  fi
                  ;;
                *)
                  echo 'unknown state, bailing out'
                  exit 0
                  ;;
              esac
              if test -e /var/lib/sync-containers3/${ctr.name}/incomplete; then
                echo 'data is inconistent, start aborted'
                exit 1
              fi
              consul kv put containers/${ctr.name} "$(jq -cn '{host: "${config.networking.hostName}", time: now}')" >/dev/null
              consul lock -verbose -monitor-retry=100 -timeout 30s -name container_${ctr.name} container_${ctr.name} ${pkgs.writers.writeBash "${ctr.name}-start" ''
                set -efu
                cryptsetup luksOpen --key-file ${ctr.luksKey} /var/lib/sync-containers3/${ctr.name}/disk ${ctr.name} || :
                mkdir -p /var/lib/sync-containers3/${ctr.name}/state
                mountpoint /var/lib/sync-containers3/${ctr.name}/state || mount /dev/mapper/${ctr.name} /var/lib/sync-containers3/${ctr.name}/state
                /run/current-system/sw/bin/nixos-container start ${ctr.name}
                # wait for system to become reachable for the first time
                retry -t 10 -d 10 -- /run/wrappers/bin/ping -q -c 1 ${ctr.name}.r > /dev/null
                systemctl start ${ctr.name}_watcher.service
                while systemctl is-active container@${ctr.name}.service >/devnull && /run/wrappers/bin/ping -q -c 3 ${ctr.name}.r >/dev/null; do
                  consul kv put containers/${ctr.name} "$(jq -cn '{host: "${config.networking.hostName}", time: now}')" >/dev/null
                  sleep 10
                done
              ''}
            '';
          };
        }; }
      ]) (lib.attrValues cfg.containers)));

      systemd.timers = lib.mapAttrs' (n: ctr: lib.nameValuePair "${ctr.name}_syncer" {
        timerConfig = {
          RandomizedDelaySec = 100;
        };
      }) cfg.containers;

      users.groups = lib.mapAttrs' (_: ctr: lib.nameValuePair "${ctr.name}_container" {
      }) cfg.containers;
      users.users = lib.mapAttrs' (_: ctr: lib.nameValuePair "${ctr.name}_container" ({
        group = "container_${ctr.name}";
        isNormalUser = true;
        uid = slib.genid_uint31 "container_${ctr.name}";
        home = "/var/lib/sync-containers3/${ctr.name}";
        createHome = true;
        homeMode = "705";
      })) cfg.containers;

    })
    (lib.mkIf (cfg.containers != {}) {
      # networking
      networking.networkmanager.unmanaged = [ "ctr0" ];
      networking.interfaces.dummy0.virtual = true;
      networking.bridges.ctr0.interfaces = [ "dummy0" ];
      networking.interfaces.ctr0.ipv4.addresses = [{
        address = "10.233.0.1";
        prefixLength = 24;
      }];
      systemd.services."dhcpd-ctr0" = {
        wantedBy = [ "multi-user.target" ];
        after = [ "network.target" ];
        serviceConfig = {
          Type = "forking";
          Restart = "always";
          DynamicUser = true;
          StateDirectory = "dhcpd-ctr0";
          User = "dhcpd-ctr0";
          Group = "dhcpd-ctr0";
          AmbientCapabilities = [
           "CAP_NET_RAW"          # to send ICMP messages
           "CAP_NET_BIND_SERVICE" # to bind on DHCP port (67)
          ];
          ExecStartPre = "${pkgs.coreutils}/bin/touch /var/lib/dhcpd-ctr0/dhcpd.leases";
          ExecStart = "${pkgs.dhcp}/bin/dhcpd -4 -lf /var/lib/dhcpd-ctr0/dhcpd.leases -cf ${pkgs.writeText "dhpd.conf" ''
            default-lease-time 600;
            max-lease-time 7200;
            authoritative;
            ddns-update-style interim;
            log-facility local1; # see dhcpd.nix

            option subnet-mask 255.255.255.0;
            option routers 10.233.0.1;
            # option domain-name-servers 8.8.8.8; # TODO configure dns server
            subnet 10.233.0.0 netmask 255.255.255.0 {
              range 10.233.0.10 10.233.0.250;
            }
          ''} ctr0";
        };
      };
    })
    (lib.mkIf cfg.inContainer.enable {
      users.groups.container_sync = {};
      users.users.container_sync = {
        group = "container_sync";
        uid = slib.genid_uint31 "container_sync";
        isNormalUser = true;
        home = "/var/lib/self";
        createHome = true;
        openssh.authorizedKeys.keys = [
          cfg.inContainer.pubkey
        ];
      };
    })
  ];
}