1 files changed, 82 insertions, 0 deletions
diff --git a/nixpkgs/nixos/modules/services/networking/strongswan-swanctl/param-lib.nix b/nixpkgs/nixos/modules/services/networking/strongswan-swanctl/param-lib.nix
new file mode 100644
index 00000000000..2bbb39a7604
--- /dev/null
+++ b/nixpkgs/nixos/modules/services/networking/strongswan-swanctl/param-lib.nix
@@ -0,0 +1,82 @@
+lib :
+
+with lib;
+
+rec {
+  paramsToConf = cfg : ps : mkConf 0 (paramsToRenderedStrings cfg ps);
+
+  # mkConf takes an indentation level (which usually starts at 0) and a nested
+  # attribute set of strings and will render that set to a strongswan.conf style
+  # configuration format. For example:
+  #
+  #   mkConf 0 {a = "1"; b = { c = { "foo" = "2"; "bar" = "3"; }; d = "4";};}   =>   ''
+  #   a = 1
+  #   b {
+  #     c {
+  #       foo = 2
+  #       bar = 3
+  #     }
+  #     d = 4
+  #   }''
+  mkConf = indent : ps :
+    concatMapStringsSep "\n"
+      (name:
+        let value = ps.${name};
+            indentation = replicate indent " ";
+        in
+        indentation + (
+          if isAttrs value
+          then "${name} {\n" +
+                 mkConf (indent + 2) value + "\n" +
+               indentation + "}"
+          else "${name} = ${value}"
+        )
+      )
+      (attrNames ps);
+
+  replicate = n : c : concatStrings (builtins.genList (_x : c) n);
+
+  # `paramsToRenderedStrings cfg ps` converts the NixOS configuration `cfg`
+  # (typically the "config" argument of a NixOS module) and the set of
+  # parameters `ps` (an attribute set where the values are constructed using the
+  # parameter constructors in ./param-constructors.nix) to a nested attribute
+  # set of strings (rendered parameters).
+  paramsToRenderedStrings = cfg : ps :
+    filterEmptySets (
+      (mapParamsRecursive (path: name: param:
+        let value = attrByPath path null cfg;
+        in optionalAttrs (value != null) (param.render name value)
+      ) ps));
+
+  filterEmptySets = set : filterAttrs (n: v: (v != null)) (mapAttrs (name: value:
+    if isAttrs value
+    then let value' = filterEmptySets value;
+         in if value' == {}
+            then null
+            else value'
+    else value
+  ) set);
+
+  # Recursively map over every parameter in the given attribute set.
+  mapParamsRecursive = mapAttrsRecursiveCond' (as: (!(as ? _type && as._type == "param")));
+
+  mapAttrsRecursiveCond' = cond: f: set:
+    let
+      recurse = path: set:
+        let
+          g =
+            name: value:
+            if isAttrs value && cond value
+              then { ${name} = recurse (path ++ [name]) value; }
+              else f (path ++ [name]) name value;
+        in mapAttrs'' g set;
+    in recurse [] set;
+
+  mapAttrs'' = f: set:
+    foldl' (a: b: a // b) {} (map (attr: f attr set.${attr}) (attrNames set));
+
+  # Extract the options from the given set of parameters.
+  paramsToOptions = ps :
+    mapParamsRecursive (_path: name: param: { ${name} = param.option; }) ps;
+
+}