{
  config,
  lib,
  pkgs,
  utils,
  ...
}:

let
  inherit (lib) mkIf;
  cfg = config.home-manager;

  serviceEnvironment = lib.mkMerge [
    (mkIf cfg.verbose { VERBOSE = "1"; })

    (mkIf (cfg.backupFileExtension != null) {
      HOME_MANAGER_BACKUP_EXT = cfg.backupFileExtension;
    })

    (mkIf cfg.overwriteBackup { HOME_MANAGER_BACKUP_OVERWRITE = "1"; })
  ];
in
{
  imports = [ ./common.nix ];

  config = lib.mkMerge [
    {
      home-manager = {
        extraSpecialArgs.nixosConfig = config;

        sharedModules = [
          {
            key = "home-manager#nixos-shared-module";

            config = {
              # The per-user directory inside /etc/profiles is not known by
              # fontconfig by default.
              fonts.fontconfig.enable = lib.mkDefault (cfg.useUserPackages && config.fonts.fontconfig.enable);

              # Inherit glibcLocales setting from NixOS.
              i18n.glibcLocales = lib.mkDefault config.i18n.glibcLocales;
            };
          }
        ];
      };
    }
    (mkIf (cfg.users != { }) {
      systemd.services = lib.mapAttrs' (
        _: usercfg:
        let
          username = usercfg.home.username;
          driverVersion = if cfg.enableLegacyProfileManagement then "0" else "1";
        in
        lib.nameValuePair "home-manager-${utils.escapeSystemdPath username}" {
          description = "Home Manager environment for ${username}";
          wantedBy = [ "multi-user.target" ];
          wants = [ "nix-daemon.socket" ];
          after = [ "nix-daemon.socket" ];
          before = [ "systemd-user-sessions.service" ];

          environment = serviceEnvironment;

          unitConfig = {
            RequiresMountsFor = usercfg.home.homeDirectory;
          };

          stopIfChanged = false;

          serviceConfig = {
            User = usercfg.home.username;
            Type = "oneshot";
            TimeoutStartSec = "5m";
            SyslogIdentifier = "hm-activate-${username}";

            ExecStart =
              let
                systemctl = "XDG_RUNTIME_DIR=\${XDG_RUNTIME_DIR:-/run/user/$UID} systemctl";

                sed = "${pkgs.gnused}/bin/sed";

                exportedSystemdVariables = lib.concatStringsSep "|" [
                  "DBUS_SESSION_BUS_ADDRESS"
                  "DISPLAY"
                  "WAYLAND_DISPLAY"
                  "XAUTHORITY"
                  "XDG_RUNTIME_DIR"
                ];

                setupEnv = pkgs.writeScript "hm-setup-env" ''
                  #! ${pkgs.runtimeShell} -el

                  # The activation script is run by a login shell to make sure
                  # that the user is given a sane environment.
                  # If the user is logged in, import variables from their current
                  # session environment.
                  eval "$(
                    ${systemctl} --user show-environment 2> /dev/null \
                    | ${sed} -En '/^(${exportedSystemdVariables})=/s/^/export /p'
                  )"

                  exec "$1/activate" --driver-version ${driverVersion}
                '';
              in
              "${setupEnv} ${usercfg.home.activationPackage}";
          };
        }
      ) cfg.users;
    })
  ];
}
