refactor: Make more modular and do some refactoring

flake.nix

@@ -91,5 +91,8 @@
 
       # Expose artifacts to all systems, but they are always built for x86_64-linux
       packages = forAllSystems (_: artifacts);
+
+      # Expose host type modules for external use
+      nixosModules = import ./installer/modules.nix { inherit inputs; };
     };
 }

hosts/boot.nix

@@ -12,7 +12,8 @@
 # the target device and swap size.
 
 {
-  options.ugaif.host = {
+  options.ugaif = {
+    host = {
       filesystem = {
         device = lib.mkOption {
           type = lib.types.str;
@@ -38,9 +39,33 @@
       };
     };
 
+    system.gc = {
+      enable = lib.mkOption {
+        type = lib.types.bool;
+        default = true;
+        description = "Whether to enable automatic garbage collection.";
+      };
+      frequency = lib.mkOption {
+        type = lib.types.str;
+        default = "weekly";
+        description = "How often to run garbage collection (systemd timer format).";
+      };
+      retentionDays = lib.mkOption {
+        type = lib.types.int;
+        default = 30;
+        description = "Number of days to keep old generations before deletion.";
+      };
+      optimise = lib.mkOption {
+        type = lib.types.bool;
+        default = true;
+        description = "Whether to automatically optimize the Nix store.";
+      };
+    };
+  };
+
   config = {
     # Enable Disko for declarative partitioning
-    disko.enableConfig = true;
+    disko.enableConfig = lib.mkDefault true;
 
     disko.devices = {
       disk.main = {

hosts/common.nix

@@ -0,0 +1,47 @@
+# ============================================================================
+# Common Modules
+# ============================================================================
+# This module contains all the common configuration shared by all host types.
+# It includes:
+# - Boot and user configuration
+# - Software configurations
+# - User management (users.nix)
+# - Home Manager integration
+# - Secret management (agenix)
+# - Disk partitioning (disko)
+# - System-wide Nix settings (experimental features, garbage collection)
+
+{ inputs }:
+{
+  config,
+  lib,
+  ...
+}:
+{
+  imports = [
+    ./boot.nix
+    ./user-config.nix
+    ../sw
+    ../users.nix
+    inputs.home-manager.nixosModules.home-manager
+    inputs.agenix.nixosModules.default
+    inputs.disko.nixosModules.disko
+  ];
+
+  system.stateVersion = "25.11";
+
+  nix.settings.experimental-features = [
+    "nix-command"
+    "flakes"
+  ];
+
+  # Automatic Garbage Collection
+  nix.gc = lib.mkIf config.ugaif.system.gc.enable {
+    automatic = true;
+    dates = config.ugaif.system.gc.frequency;
+    options = "--delete-older-than ${toString config.ugaif.system.gc.retentionDays}d";
+  };
+
+  # Optimize storage
+  nix.optimise.automatic = config.ugaif.system.gc.optimise;
+}

hosts/default.nix

@@ -16,38 +16,6 @@
 let
   nixpkgs = inputs.nixpkgs;
   lib = nixpkgs.lib;
-  home-manager = inputs.home-manager;
-  agenix = inputs.agenix;
-  disko = inputs.disko;
-
-  # Modules shared by all hosts
-  commonModules = [
-    ./boot.nix
-    ./user-config.nix
-    ../users.nix
-    ../sw
-    home-manager.nixosModules.home-manager
-    agenix.nixosModules.default
-    disko.nixosModules.disko
-    {
-      system.stateVersion = "25.11";
-      nix.settings.experimental-features = [
-        "nix-command"
-        "flakes"
-      ];
-
-      # Automatic Garbage Collection
-      nix.gc = {
-        automatic = true;
-        dates = "weekly";
-        options = "--delete-older-than 30d";
-      };
-
-      # Optimize storage
-      nix.optimise.automatic = true;
-    }
-  ];
-
   # Helper to create a single NixOS system configuration
   mkHost =
     {
@@ -72,8 +40,7 @@ let
       ) accounts;
 
       allModules =
-        commonModules
+        userFlakeModules
-        ++ userFlakeModules
         ++ extraModules
         ++ [
           { networking.hostName = hostName; }
@@ -164,7 +131,7 @@ let
       typeFile = ./types + "/${type}.nix";
       modules =
         if builtins.pathExists typeFile then
-          import typeFile { inherit inputs; }
+          [ (import typeFile { inherit inputs; }) ]
         else
           throw "Host type '${type}' not found in hosts/types/";
     in

hosts/types/nix-desktop.nix

@@ -1,14 +1,15 @@
 { inputs, ... }:
-[
+{
-  (
-    {
   config,
   lib,
   modulesPath,
   ...
-    }:
+}:
-    {
+{
-      imports = [ (modulesPath + "/installer/scan/not-detected.nix") ];
+  imports = [
+    (import ../common.nix { inherit inputs; })
+    (modulesPath + "/installer/scan/not-detected.nix")
+  ];
 
   boot.initrd.availableKernelModules = [
     "xhci_pci"
@@ -34,10 +35,7 @@
   nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
 
   hardware.cpu.intel.updateMicrocode = lib.mkDefault config.hardware.enableRedistributableFirmware;
-    }
+
-  )
-  {
   ugaif.sw.enable = true;
-    ugaif.sw.type = "desktop";
+  ugaif.sw.type = lib.mkDefault "desktop";
-  }
+}
-]

hosts/types/nix-ephemeral.nix

@@ -1,16 +1,17 @@
 { inputs, ... }:
-[
+{
-  (
-    {
   config,
   lib,
   modulesPath,
   ...
-    }:
+}:
-    {
+{
   # This host type is for ephemeral, diskless systems (e.g. kiosks, netboot clients).
   # It runs entirely from RAM and does not persist state across reboots.
-      imports = [ (modulesPath + "/installer/scan/not-detected.nix") ];
+  imports = [
+    (import ../common.nix { inherit inputs; })
+    (modulesPath + "/installer/scan/not-detected.nix")
+  ];
 
   boot.initrd.availableKernelModules = [
     "xhci_pci"
@@ -54,10 +55,7 @@
 
   nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
   hardware.cpu.intel.updateMicrocode = lib.mkDefault config.hardware.enableRedistributableFirmware;
-    }
+
-  )
-  {
   ugaif.sw.enable = true;
-    ugaif.sw.type = "stateless-kiosk";
+  ugaif.sw.type = lib.mkDefault "stateless-kiosk";
-  }
+}
-]

hosts/types/nix-laptop.nix

@@ -1,14 +1,15 @@
 { inputs, ... }:
-[
+{
-  (
-    {
   config,
   lib,
   modulesPath,
   ...
-    }:
+}:
-    {
+{
-      imports = [ (modulesPath + "/installer/scan/not-detected.nix") ];
+  imports = [
+    (import ../common.nix { inherit inputs; })
+    (modulesPath + "/installer/scan/not-detected.nix")
+  ];
 
   boot.initrd.availableKernelModules = [
     "xhci_pci"
@@ -48,10 +49,7 @@
       HandleLidSwitchDocked = "ignore";
     };
   };
-    }
+
-  )
-  {
   ugaif.sw.enable = true;
-    ugaif.sw.type = "desktop";
+  ugaif.sw.type = lib.mkDefault "desktop";
-  }
+}
-]

hosts/types/nix-lxc.nix

@@ -1,14 +1,17 @@
 { inputs, ... }:
-[
+{
-  inputs.vscode-server.nixosModules.default
-  (
-    {
   config,
   lib,
   modulesPath,
   ...
-    }:
+}:
-    {
+{
+  imports = [
+    (import ../common.nix { inherit inputs; })
+    inputs.vscode-server.nixosModules.default
+    "${modulesPath}/virtualisation/proxmox-lxc.nix"
+  ];
+
   nix.settings.trusted-users = [
     "root"
     "engr-ugaif"
@@ -17,9 +20,7 @@
     "nix-command"
     "flakes"
   ];
-      imports = [
+
-        "${modulesPath}/virtualisation/proxmox-lxc.nix"
-      ];
   boot.isContainer = true;
   boot.loader.systemd-boot.enable = lib.mkForce false;
   disko.enableConfig = lib.mkForce false;
@@ -39,10 +40,7 @@
     "lxc"
     "proxmox"
   ];
-    }
+
-  )
-  {
   ugaif.sw.enable = true;
-    ugaif.sw.type = "headless";
+  ugaif.sw.type = lib.mkDefault "headless";
-  }
+}
-]

hosts/types/nix-surface.nix

@@ -1,22 +1,24 @@
 { inputs, ... }:
-[
+{
-  (
-    {
   config,
   lib,
   pkgs,
   modulesPath,
   ...
-    }:
+}:
-    let
+let
   refSystem = inputs.nixpkgs-old-kernel.lib.nixosSystem {
     system = pkgs.stdenv.hostPlatform.system;
     modules = [ inputs.nixos-hardware.nixosModules.microsoft-surface-go ];
   };
   refKernelPackages = refSystem.config.boot.kernelPackages;
-    in
+in
-    {
+{
-      imports = [ (modulesPath + "/installer/scan/not-detected.nix") ];
+  imports = [
+    (import ../common.nix { inherit inputs; })
+    (modulesPath + "/installer/scan/not-detected.nix")
+    inputs.nixos-hardware.nixosModules.microsoft-surface-go
+  ];
 
   boot.initrd.availableKernelModules = [
     "xhci_pci"
@@ -49,11 +51,7 @@
   nixpkgs.hostPlatform = lib.mkDefault "x86_64-linux";
 
   hardware.cpu.intel.updateMicrocode = lib.mkDefault config.hardware.enableRedistributableFirmware;
-    }
+
-  )
-  inputs.nixos-hardware.nixosModules.microsoft-surface-go
-  {
   ugaif.sw.enable = true;
-    ugaif.sw.type = "tablet-kiosk";
+  ugaif.sw.type = lib.mkDefault "tablet-kiosk";
-  }
+}
-]

hosts/types/nix-wsl.nix

@@ -1,10 +1,16 @@
 { inputs, ... }:
-[
+{
+  lib,
+  config,
+  ...
+}:
+{
+  imports = [
+    (import ../common.nix { inherit inputs; })
     inputs.nixos-wsl.nixosModules.default
     inputs.vscode-server.nixosModules.default
-  (
+  ];
-    { lib, config, ... }:
+
-    {
   options.ugaif.host.wsl.user = lib.mkOption {
     type = lib.types.str;
     default = "engr-ugaif";
@@ -17,7 +23,7 @@
 
     # Enable the headless software profile
     ugaif.sw.enable = true;
-        ugaif.sw.type = "headless";
+    ugaif.sw.type = lib.mkDefault "headless";
 
     # Fix for VS Code Server in WSL if needed, though vscode-server input exists
     services.vscode-server.enable = true;
@@ -34,6 +40,4 @@
     ugaif.host.filesystem.device = "/dev/null";
     ugaif.host.filesystem.swapSize = "0G";
   };
-    }
+}
-  )
-]

installer/modules.nix

@@ -0,0 +1,20 @@
+# ============================================================================
+# Host Type Modules Export
+# ============================================================================
+# This file exposes each host type as a reusable NixOS module that can be
+# imported by external flakes or configurations.
+#
+# Usage in another flake:
+#   inputs.nixos-systems.nixosModules.nix-desktop
+#   inputs.nixos-systems.nixosModules.nix-laptop
+#   etc.
+
+{ inputs }:
+{
+  nix-desktop = import ../hosts/types/nix-desktop.nix { inherit inputs; };
+  nix-laptop = import ../hosts/types/nix-laptop.nix { inherit inputs; };
+  nix-surface = import ../hosts/types/nix-surface.nix { inherit inputs; };
+  nix-lxc = import ../hosts/types/nix-lxc.nix { inherit inputs; };
+  nix-wsl = import ../hosts/types/nix-wsl.nix { inherit inputs; };
+  nix-ephemeral = import ../hosts/types/nix-ephemeral.nix { inherit inputs; };
+}