{
  config,
  lib,
  pkgs,
  ...
}:
with lib;
{
  imports = attrValues (modulesIn ./.);

  nixfiles.modules = {
    ark.enable = true;

    wireguard.client.enable = true;

    syncthing.enable = true;

    openssh.server = {
      enable = true;
      port = 22;
    };

    android.enable = true;
    beets.enable = true;
    bluetooth.enable = true;
    libvirtd.enable = true;
    mpd.enable = true;
    qutebrowser.enable = true;

    hyprland.enable = true;
  };

  hm = {
    home.packages = with pkgs; [
      calibre
      inkscape
      krita
      paper-plane
      qolibri
      radeontop
      rocmPackages.rocm-smi
      vial
      wacomtablet
    ];

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

      mpv = {
        profiles =
          let
            mapShaders = map (args: toString (pkgs.fetchurl args));
            cfl-prediction = mapShaders [
              {
                url = "https://raw.githubusercontent.com/Artoriuz/glsl-chroma-from-luma-prediction/471c65dd3915d39e7ef69957ab63e006125fbb88/CfL_Prediction.glsl";
                sha256 = "sha256-Mgb1KqF1EPPzR3SCVr9S4XzVmZkYEEFIHSp59RZ9wq8=";
              }
            ];
            ravu-lite-ar-r4 = mapShaders [
              {
                url = "https://raw.githubusercontent.com/bjin/mpv-prescalers/b3f0a59d68f33b7162051ea5970a5169558f0ea2/compute/ravu-lite-ar-r4.hook";
                sha256 = "sha256-gyBAv/Sf75CobVUugeTOhy54B9z8iIoJSJgnLopfMsY=";
              }
            ];
            ssimdownscaler = mapShaders [
              {
                url = "https://gist.githubusercontent.com/igv/36508af3ffc84410fe39761d6969be10/raw/575d13567bbe3caa778310bd3b2a4c516c445039/SSimDownscaler.glsl";
                sha256 = "sha256-AEq2wv/Nxo9g6Y5e4I9aIin0plTcMqBG43FuOxbnR1w=";
              }
            ];
          in
          {
            # TODO Fix profile conditionals.
            "qhd-downscale" = {
              dscale = "lanczos";
              linear-downscaling = false;
              glsl-shaders-append = ssimdownscaler;
            };

            "qhd-upscale" = {
              glsl-shaders-append = cfl-prediction ++ ravu-lite-ar-r4;
            };
          };

        config = {
          profile = "gpu-hq";
          vo = "gpu-next";
          gpu-api = "vulkan";
          hwdec = "auto";

          deband = true;
          deband-iterations = 4;
          deband-threshold = 35;
          deband-range = 16;
          deband-grain = 5;

          temporal-dither = true;
          dither-depth = "auto";
          dither = "fruit";

          interpolation = true;
          video-sync = "display-resample";
          tscale = "oversample";

          target-prim = "auto";
          target-trc = "auto";
          vf = "format=colorlevels=full:colormatrix=auto";
          video-output-levels = "full";

          glsl-shaders-append = map (text: toString (pkgs.writeText "shader.hook" text)) [
            ''
              //!HOOK LUMA
              //!BIND HOOKED
              #define STRENGTH 48.0
              float mod289(float x)  { return x - floor(x / 289.0) * 289.0; }
              float permute(float x) { return mod289((34.0*x + 1.0) * x); }
              float rand(float x)    { return fract(x / 41.0); }
              vec4 hook()  {
                  vec3 _m = vec3(HOOKED_pos, 1.0) + vec3(1.0);
                  float h = permute(permute(permute(_m.x)+_m.y)+_m.z);
                  vec4 noise;
                  noise.x = rand(h);
                  return HOOKED_tex(HOOKED_pos) + vec4(STRENGTH/8192.0) * (noise - 0.5);
              }
            ''
            ''
              //!HOOK CHROMA
              //!BIND HOOKED
              #define STRENGTH 48.0
              float mod289(float x)  { return x - floor(x / 289.0) * 289.0; }
              float permute(float x) { return mod289((34.0*x + 1.0) * x); }
              float rand(float x)    { return fract(x / 41.0); }
              vec4 hook()  {
                  vec3 _m = vec3(HOOKED_pos, 0.5) + vec3(1.0);
                  float h = permute(permute(permute(_m.x)+_m.y)+_m.z);
                  vec4 noise;
                  noise.x = rand(h); h = permute(h);
                  noise.y = rand(h);
                  return HOOKED_tex(HOOKED_pos) + vec4(STRENGTH/8192.0) * (noise - 0.5);
              }
            ''
          ];
        };
      };
    };

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

      xsettingsd.settings."Xft/DPI" = "93";
    };
  };

  services = {
    languagetool = {
      enable = true;
      port = 8081;
      allowOrigin = "*";
    };

    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 ];

    xserver.wacom.enable = true;
  };

  nix.settings = {
    max-jobs = 8;
    cores = 30;
  };

  # 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_latest;

    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" ];

    # These pools were configured manually with a specific mountpoint.
    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}".neededForBoot = true;
  };

  systemd.mounts = [
    {
      type = "tmpfs";
      what = "tmpfs";
      where = "/var/tmp";
      mountConfig.Options = [
        "huge=within_size"
        "mode=1777"
        "noatime"
        "nodev"
        "nosuid"
        "rw"
        "size=25%"
      ];
    }
  ];

  zramSwap = {
    enable = true;
    memoryPercent = 25;
  };

  users = {
    users.builder = {
      isSystemUser = true;
      group = "builder";
      openssh.authorizedKeys.keys = [
        "ssh-ed25519 @PUBLIC_KEY@ root@ilmare"
      ];
      useDefaultShell = true;
    };
    groups.builder = { };
  };

  nix.settings.trusted-users = [ "builder" ];
}