nixos/users/default.nix

# Users
/**
  This module contains users' configuration which is declared on system level.
  It includes user's password, shell, etc.
  Parameters is imported from `about.json` in user's folder. File can have these keys (may be expanded in future):

  - `realName`: User's real name  (optionally)
  - `extraGroups`: groups (optionally)
  - `shell`: User's shell
  - `session`: User's default graphical session (optionally)

  Session must have format of "{type}:{session}" where type is one of `co` (short for "compositor") and `de` (short for "desktop environment").
  This `type` is actually important, because it depends where nix will search corresponding option for enabling your session.
  If `co`, it will search it in `programs.*`, and if `de`, in `services.desktopManager.*`

  User's face (optionally)
    - if any, should be located at users/{user}/face.png
    - i prefer store this encrypted, but you can keep it in clear text

  User's password must be stored at users/{user}/password.yaml and encrypted with sops. Format of unencrypted file:
    ```yaml
    # {your password}
    {username}:
      userPassword: {hash}
    ```
    where `{hash}` is result of `echo {your password} | mkpasswd -s`

    Wallpapers can be `png` or `jpg` format, and must be stored at `users/{user}/wallpaper.{ext}`
*/
{
  lib,
  pkgs,
  cfg,
  config,
  inputs,
  ...
}:
lib.foldl' (acc: obj: lib.recursiveUpdate acc obj) { } (
  lib.lists.flatten [
    # Import required modules
    {
      imports = [
        inputs.home-manager.nixosModules.default
      ];
    }

    # Configure users' passwords as sops secret.
    (map (user: {
      sops.secrets."${user}/userPassword" = {
        sopsFile = ./${user}/password.yaml;
        neededForUsers = true;
      };
    }) cfg.usersList)

    # Configure users
    (map (user: {
      users.users.${user} =
        let
          cfg = builtins.fromJSON (builtins.readFile ./${user}/about.json);
        in
        {
          description = cfg.realName or user;
          hashedPasswordFile = config.sops.secrets."${user}/userPassword".path;
          isNormalUser = true;
          shell = pkgs."${cfg.shell}";
          extraGroups = cfg.extraGroups or [ ];
        };
    }) cfg.usersList)

    # Configurure home-manager
    {
      home-manager = {
        backupFileExtension = "backup-${toString inputs.self.lastModified}";
        extraSpecialArgs = {
          inherit inputs;
        };
      };
    }
    (map (user: {
      home-manager.users.${user} = {
        nixpkgs.config.allowUnfree = true;

        imports = [
          ./${user}/modules

          inputs.stylix.homeModules.stylix
        ];
        stylix = lib.mkIf (!cfg.headless) {
          enable = true;
          image =
            if builtins.pathExists ./${user}/wallpaper.png then
              ./${user}/wallpaper.png
            else
              ./${user}/wallpaper.jpg;
        };
        home.stateVersion = config.system.stateVersion;
      };
    }) cfg.usersList)

    # Configure DM and users' default sessions
    (lib.optionalAttrs (!cfg.headless) {
      services.displayManager.gdm.enable = true;
    })

    (map (
      user:
      lib.optionalAttrs (!cfg.headless) {
        systemd.tmpfiles.settings."20-gdm-default-session" = {
          "/run/tmpfiles/var/lib/AccountsService/users/${user}".f = {
            argument = "${lib.generators.toINI { } {
              User = {
                Session = toString (
                  builtins.tail (
                    lib.splitString ":" (builtins.fromJSON (builtins.readFile ./${user}/about.json)).session
                  )
                );
                SystemAccount = false;
              }
              // (
                let
                  pic = ./${user}/face.png;
                in
                if builtins.pathExists pic then { Icon = "${pic}"; } else { }
              );
            }}";
          };
          "/var/lib/AccountsService/users/${user}"."L+" = {
            argument = "/run/tmpfiles/var/lib/AccountsService/users/${user}";
          };
        };
      }
    ) cfg.usersList)

    (map (
      user:
      lib.optionalAttrs (!cfg.headless) (
        let
          __session = lib.splitString ":" (builtins.fromJSON (builtins.readFile ./${user}/about.json))
          .session;
          sessionType = (builtins.head __session);
          session = toString (builtins.tail __session);
        in
        assert sessionType == "co" || sessionType == "de";
        if sessionType == "co" then
          {
            programs.${session}.enable = true;
          }
        else if sessionType == "de" then
          { services.desktopManager.${session}.enable = true; }
        else
          { }
      )
    ) cfg.usersList)
  ]
)