move old nixos-config over here

common/nix.nix

@@ -1,15 +1,47 @@
-{ outputs, ... }:
 {
+  inputs,
+  outputs,
+  lib,
+  config,
+  pkgs,
+  ...
+}:
+
+{
+  nix =
+    let
+      flakeInputs = lib.filterAttrs (_: lib.isType "flake") inputs;
+    in
+    {
+      settings = {
+        auto-optimise-store = true;
+        experimental-features = "nix-command flakes";
+        flake-registry = "";
+        # Workaround for https://github.com/NixOS/nix/issues/9574
+        nix-path = config.nix.nixPath;
+        substituters = [ "https://cache.nixos.org/" ];
+        trusted-public-keys = [ "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY=" ];
+      };
+      channel.enable = false;
+      registry = lib.mapAttrs (_: flake: { inherit flake; }) flakeInputs;
+      nixPath = lib.mapAttrsToList (n: _: "${n}=flake:${n}") flakeInputs;
+    };
+
   nixpkgs = {
-    config.allowUnfree = true;
     overlays = [
       outputs.overlays.additions
       outputs.overlays.modifications
       outputs.overlays.unstable-packages
     ];
+    config.allowUnfree = true;
   };
 
-  programs.home-manager.enable = true;
+  programs.nh = {
+    enable = true;
+    clean.enable = true;
+    clean.extraArgs = "--keep-since 14d --keep 5";
+  };
+  programs.nix-ld.enable = true;
 
-  systemd.user.startServices = "sd-switch";
+  environment.systemPackages = with pkgs; [ nvd ];
 }