{ self, inputs, pkgs, lib, config, ... }:
let
  cfg = config.lab.k3s;

  k3s-cni-plugins = pkgs.buildEnv {
    name = "k3s-cni-plugins";
    paths = with pkgs; [
      cni-plugins
      cni-plugin-flannel
    ];
  };

  image = pkgs.nix-snapshotter.buildImage {
    name = "redis";
    resolvedByNix = true;
    config = {
      entrypoint = [ "${pkgs.redis}/bin/redis-server" ];
    };
  };
in
{
  options.lab.k3s = {
    enable = lib.mkOption {
      default = false;
      type = lib.types.bool;
      description = ''
        Whether to run k3s on this server.
      '';
    };

    role = lib.mkOption {
      default = "server";
      type = lib.types.str;
      description = ''
        Whether to run k3s as a server or an agent.
      '';
    };

    clusterInit = lib.mkOption {
      default = false;
      type = lib.types.bool;
      description = ''
        Whether this node should initialize the K8s cluster.
      '';
    };

    serverAddr = lib.mkOption {
      default = null;
      type = with lib.types; nullOr str;
      description = ''
        Address of the server whose cluster this server should join.
        Leaving this empty will make the server initialize the cluster.
      '';
    };
  };

  config = lib.mkIf cfg.enable {
    environment.systemPackages = with pkgs; [
      k3s
      openiscsi # Required for Longhorn
      nfs-utils # Required for Longhorn
    ];

    networking = {
      nftables.enable = lib.mkForce false;
      firewall.enable = lib.mkForce false;
    };

    virtualisation.containerd = {
      enable = true;

      settings = {
        version = 2;

        proxy_plugins.nix = {
          type = "snapshot";
          address = "/run/nix-snapshotter/nix-snapshotter.sock";
        };

        plugins = {
          "io.containerd.grpc.v1.cri" = {
            stream_server_address = "127.0.0.1";
            stream_server_port = "10010";
            enable_selinux = false;
            enable_unprivileged_ports = true;
            enable_unprivileged_icmp = true;
            disable_apparmor = true;
            disable_cgroup = true;
            restrict_oom_score_adj = true;
            sandbox_image = "rancher/mirrored-pause:3.6";
            containerd.snapshotter = "nix";

            cni = {
              conf_dir = "/var/lib/rancher/k3s/agent/etc/cni/net.d/";
              bin_dir = "${k3s-cni-plugins}/bin";
            };
          };

          "io.containerd.transfer.v1.local".unpack_config = [{
            platform = "linux/amd64";
            snapshotter = "nix";
          }];
        };
      };
    };

    services = {
      nix-snapshotter.enable = true;

      k3s =
        let
          serverFlagList = [
            "--image-service-endpoint=unix:///run/nix-snapshotter/nix-snapshotter.sock"
            "--snapshotter=overlayfs"
            "--container-runtime-endpoint=unix:///run/containerd/containerd.sock"
            "--tls-san=${config.networking.fqdn}"
            "--disable=servicelb"
            "--cluster-cidr=10.42.0.0/16,2001:cafe:42::/56"
            "--service-cidr=10.43.0.0/16,2001:cafe:43::/112"
          ];

          serverFlags = builtins.concatStringsSep " " serverFlagList;
        in
        {
          enable = true;
          role = cfg.role;
          tokenFile = config.sops.secrets."k3s/serverToken".path;
          extraFlags = lib.mkIf (cfg.role == "server") (lib.mkForce serverFlags);
          clusterInit = cfg.clusterInit;
          serverAddr = lib.mkIf (! (cfg.serverAddr == null)) cfg.serverAddr;
        };

      # Required for Longhorn
      openiscsi = {
        enable = true;
        name = "iqn.2016-04.com.open-iscsi:${config.networking.fqdn}";
      };
    };

    # HACK: Symlink binaries to /usr/local/bin such that Longhorn can find them
    # when they use nsenter.
    # https://github.com/longhorn/longhorn/issues/2166#issuecomment-1740179416
    systemd.tmpfiles.rules = [
      "L+ /usr/local/bin - - - - /run/current-system/sw/bin/"
    ];

    system = lib.mkIf (cfg.role == "server") {
      activationScripts = {
        k3s-bootstrap.text = (
          let
            k3sBootstrapFile = (inputs.kubenix.evalModules.x86_64-linux {
              module = import ./bootstrap.nix;
            }).config.kubernetes.result;
          in
          ''
            mkdir -p /var/lib/rancher/k3s/server/manifests
            ln -sf ${k3sBootstrapFile} /var/lib/rancher/k3s/server/manifests/k3s-bootstrap.json
          ''
        );

        k3s-certs.text = ''
          mkdir -p /var/lib/rancher/k3s/server/tls/etcd
          cp -f ${./k3s-ca/server-ca.crt} /var/lib/rancher/k3s/server/tls/server-ca.crt
          cp -f ${./k3s-ca/client-ca.crt} /var/lib/rancher/k3s/server/tls/client-ca.crt
          cp -f ${./k3s-ca/request-header-ca.crt} /var/lib/rancher/k3s/server/tls/request-header-ca.crt
          cp -f ${./k3s-ca/etcd/peer-ca.crt} /var/lib/rancher/k3s/server/tls/etcd/peer-ca.crt
          cp -f ${./k3s-ca/etcd/server-ca.crt} /var/lib/rancher/k3s/server/tls/etcd/server-ca.crt
        '';

        docker-images =
          let
            pulledImages = (import "${self}/container-images/pulled-images.nix") pkgs lib;
            basePath = "/var/docker_images";
            linesForImage = projectName: imageName: pulledImage:
              let
                projectPath = "${basePath}/${projectName}";
              in
              ''
                mkdir -p ${projectPath}
                ln -sf ${pulledImage} ${projectPath}/${imageName}.tar
              '';
            linesForProject = projectName: project:
              let
                lines = lib.attrsets.mapAttrsToList (linesForImage projectName) project;
              in
              builtins.concatStringsSep "\n" lines;
            generateLines = projects:
              let
                lines = lib.attrsets.mapAttrsToList linesForProject projects;
              in
              builtins.concatStringsSep "\n" lines;
          in
          generateLines pulledImages;
      };
    };

    sops.secrets =
      let
        keyPathBase = "/var/lib/rancher/k3s/server/tls";
      in
      {
        "k3s/serverToken" = { };
        "k3s/keys/clientCAKey".path = "${keyPathBase}/client-ca.key";
        "k3s/keys/requestHeaderCAKey".path = "${keyPathBase}/request-header-ca.key";
        "k3s/keys/serverCAKey".path = "${keyPathBase}/server-ca.key";
        "k3s/keys/serviceKey".path = "${keyPathBase}/service.key";
        "k3s/keys/etcd/peerCAKey".path = "${keyPathBase}/etcd/peer-ca.key";
        "k3s/keys/etcd/serverCAKey".path = "${keyPathBase}/etcd/server-ca.key";
      };
  };
}