stockholm/4lib/krebs/dns.nix

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{ 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));
}