From 1f8b3f5d1a4ecff870315c8afa73e40fe67fb8a0 Mon Sep 17 00:00:00 2001
From: Christopher Bacher <mindsbackyard@gmail.com>
Date: Fri, 14 Oct 2022 01:29:48 +0200
Subject: [PATCH] lib(util): add functions for finding and acessing fragments
 ("paths") through a tree of attrSets

---
 flake.nix    |  1 +
 lib/util.nix | 22 ++++++++++++++++++++++
 2 files changed, 23 insertions(+)
 create mode 100644 lib/util.nix

diff --git a/flake.nix b/flake.nix
index 50153e1..fbe630d 100644
--- a/flake.nix
+++ b/flake.nix
@@ -9,6 +9,7 @@
 
   outputs = { self, nixpkgs, flake-utils }: with flake-utils.lib; eachSystem (with system; [ x86_64-linux aarch64-linux ]) (curSystem:
     let
+      util = import ./lib/util.nix;
       pkgs = nixpkgs.legacyPackages.${curSystem};
 
       imageName = "pihole/pihole";
diff --git a/lib/util.nix b/lib/util.nix
new file mode 100644
index 0000000..ee4b79c
--- /dev/null
+++ b/lib/util.nix
@@ -0,0 +1,22 @@
+{
+  collectAttrFragments = predicate: attrs: with builtins; let
+    _collectAttrFragments = attrs:
+      concatMap (key: _collectAttrFragmentsBelowKey key attrs.${key}) (attrNames attrs)
+    ;
+    _collectAttrFragmentsBelowKey = key: value:
+      if predicate value then [ [key] ]
+      else if isAttrs value then
+        map (fragment: [key] ++ fragment) (_collectAttrFragments value)
+      else [ ]
+    ;
+    in _collectAttrFragments attrs
+  ;
+
+  accessValueOfFragment = attrs: fragment: with builtins; let
+    _accessValueOfFragment = value: fragment:
+      if fragment == [] then value
+      else _accessValueOfFragment (value.${head fragment}) (tail fragment)
+    ;
+    in _accessValueOfFragment attrs fragment
+  ;
+}