services: migrate to nilla

modules/nilla/default.nix

@@ -1,3 +1,6 @@
 {
-  includes = [ ./builders ];
+  includes = [
+    ./builders
+    ./services.nix
+  ];
 }

modules/nilla/services.nix

@@ -0,0 +1,95 @@
+{ lib, config }:
+let
+  inherit (builtins)
+    attrNames
+    attrValues
+    concatStringsSep
+    mapAttrs
+    foldl'
+    groupBy
+    length
+    ;
+  serviceModule =
+    { config }:
+    {
+      options = {
+        host = lib.options.create {
+          type = lib.types.str;
+        };
+        ports = lib.options.create {
+          type = lib.types.list.of lib.types.port;
+          default.value = [ ];
+        };
+        hosts = lib.options.create {
+          type = lib.types.list.of lib.types.str;
+          default.value = [ config.host ];
+        };
+        module = lib.options.create {
+          type = lib.types.raw;
+          default.value = { };
+        };
+        hostModule = lib.options.create {
+          type = lib.types.attrs.of lib.types.raw;
+          default.value = { };
+        };
+      };
+    };
+
+  moduleToHostConfigs =
+    cfg:
+    lib.attrs.generate cfg.hosts (host: {
+      imports = [
+        cfg.module
+        (cfg.hostModule.${host} or { })
+      ];
+    });
+
+  maybeGetPreviousConfigs = acc: host: (acc.${host} or { imports = [ ]; }).imports;
+
+  # Copied from nixpkgs/lib/lists.nix
+  groupBy' =
+    op: nul: pred: lst:
+    mapAttrs (_name: foldl' op nul) (groupBy pred lst);
+  duplicatePorts = lib.fp.pipe [
+    attrValues
+    (map (cfg: cfg.ports))
+    lib.lists.flatten
+    (groupBy' (cnt: _: cnt + 1) 0 toString)
+    (lib.attrs.filter (_: cnt: cnt > 1))
+    attrNames
+  ] config.services;
+in
+{
+  options.services = lib.options.create {
+    type = lib.types.attrs.of (lib.types.submodule serviceModule);
+    default.value = { };
+  };
+
+  options.extraHostConfigs = lib.options.create {
+    type = lib.types.attrs.of lib.types.raw;
+    writable = false;
+    default.value = lib.fp.pipe [
+      attrValues
+      (foldl' (
+        acc: cfg:
+        acc
+        // mapAttrs (host: c: {
+          imports = c.imports ++ (maybeGetPreviousConfigs acc host);
+        }) (moduleToHostConfigs cfg)
+      ) { })
+    ] config.services;
+  };
+
+  config.assertions = [
+    {
+      assertion = duplicatePorts == [ ];
+      message =
+        let
+          plural = length duplicatePorts > 1;
+        in
+        "\nBad service config:\nThe following port${if plural then "s" else ""} ${
+          if plural then "were" else "was"
+        } declared multiple times: ${concatStringsSep ", " duplicatePorts}";
+    }
+  ];
+}