flake: home-manager: use a more modular design

This means I can easily add new hosts now.

flake/home-manager.nix

@@ -1,40 +1,50 @@
-{ self, inputs, ... }:
+{ self, inputs, lib, ... }:
+let
+  defaultModules = [
+    # Include generic settings
+    "${self}/home"
+    {
+      # Basic user information defaults
+      home.username = lib.mkDefault "ambroisie";
+      home.homeDirectory = lib.mkDefault "/home/ambroisie";
+
+      # Make it a Linux installation by default
+      targets.genericLinux.enable = lib.mkDefault true;
+
+      # Enable home-manager
+      programs.home-manager.enable = true;
+    }
+  ];
+
+  mkHome = name: system: inputs.home-manager.lib.homeManagerConfiguration {
+    # Work-around for home-manager
+    # * not letting me set `lib` as an extraSpecialArgs
+    # * not respecting `nixpkgs.overlays` [1]
+    # [1]: https://github.com/nix-community/home-manager/issues/2954
+    pkgs = import inputs.nixpkgs {
+      inherit system;
+
+      overlays = (lib.attrValues self.overlays) ++ [
+        inputs.nur.overlay
+      ];
+    };
+
+    modules = defaultModules ++ [
+      "${self}/hosts/homes/${name}"
+    ];
+
+    extraSpecialArgs = {
+      # Inject inputs to use them in global registry
+      inherit inputs;
+    };
+  };
+in
 {
   perSystem = { system, ... }: {
     # Work-around for https://github.com/nix-community/home-manager/issues/3075
     legacyPackages = {
-      homeConfigurations = {
-        ambroisie = inputs.home-manager.lib.homeManagerConfiguration {
-          # Work-around for home-manager
-          # * not letting me set `lib` as an extraSpecialArgs
-          # * not respecting `nixpkgs.overlays` [1]
-          # [1]: https://github.com/nix-community/home-manager/issues/2954
-          pkgs = import inputs.nixpkgs {
-            inherit system;
-
-            overlays = (lib.attrValues self.overlays) ++ [
-              inputs.nur.overlay
-            ];
-          };
-
-          modules = [
-            "${self}/home"
-            {
-              # The basics
-              home.username = "ambroisie";
-              home.homeDirectory = "/home/ambroisie";
-              # Let Home Manager install and manage itself.
-              programs.home-manager.enable = true;
-              # This is a generic linux install
-              targets.genericLinux.enable = true;
-            }
-          ];
-
-          extraSpecialArgs = {
-            # Inject inputs to use them in global registry
-            inherit inputs;
-          };
-        };
+      homeConfigurations = lib.mapAttrs mkHome {
+        ambroisie = system;
       };
     };
   };

hosts/homes/ambroisie/default.nix

@@ -0,0 +1,5 @@
+# Default home-manager configuration
+{ ... }:
+{
+  # Default configuration, nothing to do
+}