Implement home-manager support

home-modules/common.nix

@@ -0,0 +1,48 @@
+{ lib, pkgs, inputs, isStandalone, config, ... }:
+let
+  inherit (lib) mkMerge mkIf mkDefault mkForce;
+in
+mkMerge [
+  {
+    programs = {
+      home-manager = {
+        # Even when enabled this will only be actually installed in standalone mode
+        enable = true;
+      };
+
+      htop = {
+        enable = true;
+        settings = {};
+      };
+    };
+
+    home = {
+      language.base = mkDefault "en_IE.UTF-8";
+
+      packages = with pkgs; [
+        tree
+        iperf3
+      ];
+
+      # The flake passes a default setting, but we don't care about that
+      stateVersion = mkForce "22.05";
+    };
+  }
+  (mkIf isStandalone {
+    # Note: this only applies outside NixOS where home-manager imports nixpkgs internally
+    nixpkgs = {
+      overlays = [
+        inputs.nix.overlay
+      ];
+      config = {
+        allowUnfree = true;
+      };
+    };
+
+    home = {
+      packages = with pkgs; [
+        nix
+      ];
+    };
+  })
+]