{ config, lib, pkgs, ... }: let
  cfg = config.krebs.sync-containers3;
  slib = pkgs.stockholm.lib;
in {
  options.krebs.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;
          };
          runContainer = lib.mkOption {
            type = lib.types.bool;
            default = true;
          };
        };
      }));
    };
  };
  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
              mkdir -p /var/state/var_src
              ln -Tfrs /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 = {
          "/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;
          };
        };
      }) (lib.filterAttrs (_: ctr: ctr.runContainer) 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
                  nice --adjustment=30 rsync -a -e "ssh -i $CREDENTIALS_DIRECTORY/ssh_key" --timeout=30 container_sync@${ctr.name}.r:disk "$HOME"/disk
                  rm -f "$HOME"/incomplete
                fi
              ''}
            '';
          };
        }; }
        { "${ctr.name}_watcher" = lib.mkIf ctr.runContainer {
          path = with pkgs; [
            coreutils
            consul
            cryptsetup
            curl
            mount
            util-linux
            jq
            retry
          ];
          serviceConfig = {
            ExecStart = pkgs.writers.writeDash "${ctr.name}_watcher" ''
              set -efux
              while sleep 5; do
                # get the payload
                # check if the host reacted recently
                case $(curl -s -o /dev/null --retry 10 --retry-delay 10 -w '%{http_code}' http://127.0.0.1:8500/v1/kv/containers/${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'
                    payload=$(consul kv get containers/${ctr.name}) || continue
                    export payload
                    if [ "$(jq -rn 'env.payload | fromjson.host')" = '${config.networking.hostName}' ]; then
                      # echo 'we are the host, trying to reach container'
                      if $(retry -t 10 -d 10 -- /run/wrappers/bin/ping -q -c 1 ${ctr.name}.r > /dev/null); then
                        # echo 'container is reachable, continueing'
                        continue
                      else
                        # echo 'container seems dead, killing'
                        break
                      fi
                    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" = lib.mkIf ctr.runContainer {
          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
              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
                systemctl start ${ctr.name}_watcher.service
                retry -t 10 -d 10 -- /run/wrappers/bin/ping -q -c 1 ${ctr.name}.r > /dev/null
                while systemctl is-active container@${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
              ''}
            '';
          };
        }; }
        { "container@${ctr.name}" = lib.mkIf ctr.runContainer {
          serviceConfig = {
            ExecStop = pkgs.writers.writeDash "remove_interface" ''
              ${pkgs.iproute2}/bin/ip link del vb-${ctr.name}
            '';
          };
        }; }
      ]) (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 = "${ctr.name}_container";
        isNormalUser = true;
        uid = slib.genid_uint31 "container_${ctr.name}";
        home = "/var/lib/sync-containers3/${ctr.name}";
        createHome = true;
        homeMode = "705";
      })) cfg.containers;

      environment.systemPackages = lib.mapAttrsToList (_: ctr: (pkgs.writers.writeDashBin "${ctr.name}_init" ''
        set -efux
        export PATH=${lib.makeBinPath [
          pkgs.coreutils
          pkgs.cryptsetup
          pkgs.libxfs.bin
        ]}:$PATH
        truncate -s 5G /var/lib/sync-containers3/${ctr.name}/disk
        cryptsetup luksFormat /var/lib/sync-containers3/${ctr.name}/disk ${ctr.luksKey}
        cryptsetup luksOpen --key-file ${ctr.luksKey} /var/lib/sync-containers3/${ctr.name}/disk ${ctr.name}
        mkfs.xfs /dev/mapper/${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}
        /run/current-system/sw/bin/nixos-container run ${ctr.name} -- ${pkgs.writeDash "init" ''
          mkdir -p /var/state
        ''}
      '')) cfg.containers;
    })
    (lib.mkIf (cfg.containers != {}) {
      # networking

      # needed because otherwise we lose local dns
      environment.etc."resolv.conf".source = lib.mkForce "/run/systemd/resolve/resolv.conf";

      boot.kernel.sysctl."net.ipv4.ip_forward" = lib.mkForce 1;
      systemd.network.networks.ctr0 = {
        name = "ctr0";
        address = [
          "10.233.0.1/24"
        ];
        networkConfig = {
          # IPForward = "yes";
          # IPMasquerade = "both";
          ConfigureWithoutCarrier = true;
          DHCPServer = "yes";
        };
      };
      systemd.network.netdevs.ctr0.netdevConfig = {
        Kind = "bridge";
        Name = "ctr0";
      };
      networking.networkmanager.unmanaged = [ "ctr0" ];
      krebs.iptables.tables.filter.INPUT.rules = [
        { predicate = "-i ctr0"; target = "ACCEPT"; }
      ];
      krebs.iptables.tables.filter.FORWARD.rules = [
        { predicate = "-i ctr0"; target = "ACCEPT"; }
        { predicate = "-o ctr0"; target = "ACCEPT"; }
      ];
      krebs.iptables.tables.nat.POSTROUTING.rules = [
        { v6 = false; predicate = "-s 10.233.0.0/24"; target = "MASQUERADE"; }
      ];
    })
    (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
        ];
      };

      networking.useHostResolvConf = false;
      networking.useNetworkd = true;
      systemd.network = {
        enable = true;
        networks.eth0 = {
          matchConfig.Name = "eth0";
          DHCP = "yes";
          dhcpV4Config.UseDNS = true;
        };
      };
    })
  ];
}