{
  config,
  lib,
  pkgs,
  ...
}:
with lib; {
  nixfiles.modules = {
    ark.enable = true;

    wireguard.client.enable = true;

    syncthing.enable = true;

    openssh.server.enable = true;

    games = {
      lutris.enable = true;
      minecraft.client.enable = true;
      steam.enable = true;
    };
    android.enable = true;
    bluetooth.enable = true;
    beets.enable = true;
    libvirtd.enable = true;
    qutebrowser.enable = true;
    mpd.enable = true;
    ipfs.enable = true;
  };

  hm = {
    home.packages = with pkgs; [
      anki
      gzdoom
      kdenlive
      obs-studio
      openmw
      openttd
      radeontop
      vcmi
      vial
      xonotic
    ];

    programs = {
      beets.settings.directory = mkForce "/mnt/udata/music";

      mpv.config = {
        gpu-api = "vulkan";
        profile = "gpu-hq";
        vo = "gpu-next";
      };
    };

    services.mpd.musicDirectory = mkForce "/mnt/udata/music";
  };

  services = {
    smartd = {
      enable = true;
      notifications.mail = {
        enable = true;
        sender = "admin+smartd@${my.domain.shire}";
        recipient = "admin+smartd@${my.domain.shire}";
      };
    };

    openssh.settings = {
      KbdInteractiveAuthentication = mkForce true;
      PasswordAuthentication = mkForce true;
    };

    udev.packages = with pkgs; [vial];
  };

  # Usually stuff that is going to be compiled on this machine is going to have
  # parallelisation support enabled, so we will make sure that all cores are
  # utilised and limit the job queue to one.
  nix.settings = {
    keep-going = true;
    max-jobs = 1;
    cores = 32;
  };

  # Required[1] for using ZFS kernel modules with "unsupported" kernels.
  #
  # [1]: https://github.com/NixOS/nixpkgs/pull/121113#issuecomment-830003344
  # [1]: https://github.com/NixOS/nixpkgs/pull/230498#issuecomment-1551328615
  nixpkgs.config.allowBroken = true;

  boot = {
    kernelPackages = pkgs.linuxPackages_xanmod;

    kernelParams = [
      # Silence benign MCE errors:
      # ```
      # mce: [Hardware Error]: CPU 1: Machine Check: 0 Bank 29: ffffffffffffffff
      # mce: [Hardware Error]: TSC 0 MISC ff1fffffffffffff SYND ffffffffffffffff IPID ffffffffffffffff
      # mce: [Hardware Error]: PROCESSOR 2:a60f12 TIME 1669988017 SOCKET 0 APIC 2 microcode a601201
      # ```
      "mce=nobootlog"
      # This disables[1] User Mode Instruction Protection (UMIP)[2]. This is
      # required for some games to run via Wine.
      #
      # [1]: https://docs.kernel.org/x86/cpuinfo.html
      # [2]: https://en.wikichip.org/wiki/x86/umip
      "clearcpuid=514"
    ];

    # https://wiki.archlinux.org/title/improving_performance#Watchdogs
    blacklistedKernelModules = ["sp5100_tco"];

    # The boot drive is Samsung SSD 980 PRO 2TB.
    initrd.kernelModules = ["nvme"];

    zfs.extraPools = ["udata" "vdata"];
  };

  # Filesystem creation:
  # ```
  # mkfs.vfat -F 32 -l nixos-boot /dev/nvmeXnYpZ
  #
  # zpool create
  # -o ashift=12
  # -o autotrim=on
  # -O acltype=posixacl
  # -O xattr=sa
  # -O compression=zstd
  # -O mountpoint=none
  # nixos
  # /dev/nvmeXnYpZ
  #
  # zfs create
  # nixos/root
  #
  # zfs create
  # -o encryption=aes-256-gcm
  # -o keyformat=passphrase
  # -o mountpoint=legacy
  # nixos/root/ark
  #
  # zfs create
  # -o mountpoint=legacy
  # nixos/root/nix
  # ```
  #
  # physical structure (backside):
  # [ 1 ] [ 2 ] [ 3 ]
  # 1: disk/by-id/ata-WDC_WD20SPZX-22UA7T0_WD-WXP2E3163YW6
  # 2: disk/by-id/ata-WDC_WD20SPZX-22UA7T0_WD-WXN2E312R5HP
  # 3: disk/by-id/ata-WDC_WD20SPZX-22UA7T0_WD-WXP2E311E6P2
  #
  # physical structure (mobo M.2):
  # [ 1 ]
  # [ 2 ]
  # 1: disk/by-id/nvme-Samsung_SSD_980_PRO_2TB_S69ENF0R872526A
  # 2: disk/by-id/nvme-Samsung_SSD_980_PRO_2TB_S69ENX0T807723X
  fileSystems = {
    "/" = {
      device = "none";
      fsType = "tmpfs";
      options = ["size=8G" "mode=755"];
    };

    "/boot" = {
      device = "/dev/disk/by-uuid/1363-02E6";
      fsType = "vfat";
    };

    "/nix" = {
      device = "nixos/root/nix";
      fsType = "zfs";
      options = ["noatime"];
    };

    ${config.ark.path} = {
      device = "nixos/root/ark";
      fsType = "zfs";
      neededForBoot = true; # Required by impermanence.
    };

    # Required[1] when using impermanence with agenix. Filesystem itself is
    # defined as an `ark.directory` in `nixos/common/users.nix`.
    #
    # [1]: https://github.com/ryantm/agenix/issues/45#issuecomment-847852593
    # [1]: https://github.com/nix-community/impermanence/issues/22
    # [1]: https://github.com/NixOS/nixpkgs/pull/86967#pullrequestreview-667929259
    "/home/${my.username}" = {
      depends = [config.ark.path];
      neededForBoot = true;
    };
  };

  # No swap space is declared here because the system already has 128Gb of RAM.
  # I've only manage to hit around 100Gb mark when running large
  # computations/compiling something big. Pretty sure that a hefty chunk of it
  # was just cache and it wouldn't make me get to OOM situations.
}