1 files changed, 31 insertions, 0 deletions
diff --git a/4lib/krebs/dns.nix b/4lib/krebs/dns.nix
new file mode 100644
index 000000000..b2cf3c24c
--- /dev/null
+++ b/4lib/krebs/dns.nix
@@ -0,0 +1,31 @@
+{ lib, ... }:
+
+let
+  listset = import ./listset.nix { inherit lib; };
+in
+
+with builtins;
+with lib;
+
+rec {
+  # label = string
+
+  # TODO does it make sense to have alias = list label?
+
+  # split-by-provider :
+  #   [[label]] -> tree label provider -> listset provider alias
+  split-by-provider = as: providers:
+    foldl (m: a: listset.insert (provider-of a providers) a m) {} as;
+
+  # provider-of : alias -> tree label provider -> provider
+  # Note that we cannot use tree.get here, because path can be longer
+  # than the tree depth.
+  provider-of = a:
+    let
+      go = path: tree:
+        if typeOf tree == "string"
+          then tree
+          else go (tail path) tree.${head path};
+    in
+    go (reverseList (splitString "." a));
+}