feat: initial helm integration (thanks to @matejc)

helm2json was first implemented by matejc in
https://github.com/matejc/helm2json and incorperated in this project,
big thanks to @matejc for making this possible

helm/default.nix

@@ -0,0 +1,112 @@
+{ config, lib, pkgs, kubenix, ... }:
+
+with lib;
+
+let
+  cfg = config.kubernetes.helm;
+
+  globalConfig = config;
+
+  recursiveAttrs = mkOptionType {
+    name = "recursive-attrs";
+    description = "recursive attribute set";
+    check = isAttrs;
+    merge = loc: foldl' (res: def: recursiveUpdate res def.value) {};
+  };
+
+  parseApiVersion = apiVersion: let
+    splitted = splitString "/" apiVersion;
+  in {
+    group = if length splitted == 1 then "core" else head splitted;
+    version = last splitted;
+  };
+
+  chart2json = pkgs.callPackage ./chart2json.nix {  };
+  fetchhelm = pkgs.callPackage ./fetchhelm.nix {  };
+
+in {
+  imports = [
+    kubenix.k8s
+  ];
+
+  options.kubernetes.helm = {
+    instances = mkOption {
+      description = "Attribute set of helm instances";
+      type = types.attrsOf (types.submodule ({ config, name, ... }: {
+        options = {
+          name = mkOption {
+            description = "Helm release name";
+            type = types.str;
+            default = name;
+          };
+
+          chart = mkOption {
+            description = "Helm chart to use";
+            type = types.package;
+          };
+
+          namespace = mkOption {
+            description = "Namespace to install helm chart to";
+            type = types.nullOr types.str;
+            default = null;
+          };
+
+          values = mkOption {
+            description = "Values to pass to chart";
+            type = recursiveAttrs;
+            default = {};
+          };
+
+          kubeVersion = mkOption {
+            description = "Kubernetes version to build chart for";
+            type = types.str;
+            default = globalConfig.kubernetes.version;
+          };
+
+          overrides = mkOption {
+            description = "Overrides to apply to all chart resources";
+            type = types.listOf types.unspecified;
+            default = [];
+          };
+
+          overrideNamespace = mkOption {
+            description = "Whether to apply namespace override";
+            type = types.bool;
+            default = true;
+          };
+
+          objects = mkOption {
+            description = "Generated kubernetes objects";
+            type = types.listOf types.attrs;
+            default = [];
+          };
+        };
+
+        config.overrides = mkIf (config.overrideNamespace && config.namespace != null) [{
+          metadata.namespace = mkDefault config.namespace;
+        }];
+
+        config.objects = importJSON (chart2json {
+          inherit (config) chart name namespace values kubeVersion;
+        });
+      }));
+    };
+  };
+
+  # include helper helm methods as args
+  config._module.args.helm = {
+    fetch = fetchhelm;
+    chart2json = chart2json;
+  };
+
+  config.kubernetes.api = mkMerge (flatten (mapAttrsToList (_: instance:
+    map (object: let
+      apiVersion = parseApiVersion object.apiVersion;
+      name = object.metadata.name;
+    in {
+      "${apiVersion.group}"."${apiVersion.version}".${object.kind}."${name}" = mkMerge ([
+        object
+      ] ++ instance.overrides);
+    }) instance.objects
+  ) cfg.instances));
+}