nixos/home-assistant: add customLovelaceModules support

Allows the installation of custom lovelace modules, that can inject
css/js into the frontend and offer a wide variety of widgets.

nixos/modules/services/home-automation/home-assistant.nix

@@ -16,7 +16,8 @@ let
     cp ${format.generate "configuration.yaml" filteredConfig} $out
     sed -i -e "s/'\!\([a-z_]\+\) \(.*\)'/\!\1 \2/;s/^\!\!/\!/;" $out
   '';
-  lovelaceConfig = cfg.lovelaceConfig or {};
+  lovelaceConfig = if (cfg.lovelaceConfig == null) then {}
+    else (lib.recursiveUpdate customLovelaceModulesResources cfg.lovelaceConfig);
   lovelaceConfigFile = format.generate "ui-lovelace.yaml" lovelaceConfig;
 
   # Components advertised by the home-assistant package
@@ -64,6 +65,20 @@ let
     extraComponents = oldArgs.extraComponents or [] ++ extraComponents;
     extraPackages = ps: (oldArgs.extraPackages or (_: []) ps) ++ (cfg.extraPackages ps);
   }));
+
+  # Create a directory that holds all lovelace modules
+  customLovelaceModulesDir = pkgs.buildEnv {
+    name = "home-assistant-custom-lovelace-modules";
+    paths = cfg.customLovelaceModules;
+  };
+
+  # Create parts of the lovelace config that reference lovelave modules as resources
+  customLovelaceModulesResources = {
+    lovelace.resources = map (card: {
+      url = "/local/nixos-lovelace-modules/${card.entrypoint or card.pname}.js?${card.version}";
+      type = "module";
+    }) cfg.customLovelaceModules;
+  };
 in {
   imports = [
     # Migrations in NixOS 22.05
@@ -137,6 +152,26 @@ in {
       '';
     };
 
+    customLovelaceModules = mkOption {
+      type = types.listOf types.package;
+      default = [];
+      example = literalExpression ''
+        with pkgs.home-assistant-custom-lovelace-modules; [
+          mini-graph-card
+          mini-media-player
+        ];
+      '';
+      description = lib.mdDoc ''
+        List of custom lovelace card packages to load as lovelace resources.
+
+        Available cards can be found below `pkgs.home-assistant-custom-lovelace-modules`.
+
+        ::: {.note}
+        Automatic loading only works with lovelace in `yaml` mode.
+        :::
+      '';
+    };
+
     config = mkOption {
       type = types.nullOr (types.submodule {
         freeformType = format.type;
@@ -408,9 +443,16 @@ in {
           rm -f "${cfg.configDir}/ui-lovelace.yaml"
           ln -s /etc/home-assistant/ui-lovelace.yaml "${cfg.configDir}/ui-lovelace.yaml"
         '';
+        copyCustomLovelaceModules = if cfg.customLovelaceModules != [] then ''
+          mkdir -p "${cfg.configDir}/www"
+          ln -fns ${customLovelaceModulesDir} "${cfg.configDir}/www/nixos-lovelace-modules"
+        '' else ''
+          rm -f "${cfg.configDir}/www/nixos-lovelace-modules"
+        '';
       in
         (optionalString (cfg.config != null) copyConfig) +
-        (optionalString (cfg.lovelaceConfig != null) copyLovelaceConfig)
+        (optionalString (cfg.lovelaceConfig != null) copyLovelaceConfig) +
+        copyCustomLovelaceModules
       ;
       environment.PYTHONPATH = package.pythonPath;
       serviceConfig = let