feat(lib): add admin user using custom lib function

nix/flake-parts/meta.nix

@@ -1,8 +1,16 @@
-{ lib, inputs, ... }:
+{
+  lib,
+  config,
+  inputs,
+  ...
+}:
 let
   inherit (lib.options) mkOption;
   inherit (lib.types) path lazyAttrsOf raw;
   inherit (inputs.flake-parts.lib) mkSubmoduleOptions;
+  inherit (cfg.lib.attrsets) firstAttrNameMatching;
+  cfg = config.flake;
+  username = firstAttrNameMatching (_: v: v.primary or false) cfg.manifest.users;
 in
 {
   options.flake = mkSubmoduleOptions {
@@ -14,5 +22,13 @@ in
       type = path;
       default = "";
     };
+    admin = mkOption {
+      type = lazyAttrsOf raw;
+      default = { };
+    };
+  };
+
+  config.flake.admin = cfg.manifest.users.${username} // {
+    inherit username;
   };
 }

nix/lib/attrsets.nix

@@ -0,0 +1,54 @@
+{ lib, ... }:
+let
+  inherit (builtins) attrNames head;
+  inherit (lib.trivial) pipe;
+  inherit (lib.attrsets) filterAttrs;
+in
+{
+  flake.lib.attrsets = {
+    /**
+      `firstAttrNameMatching pred set` filters an attribute set `set` based on a predicate `pred`
+      and returns the *first* attribute name that satisfies the predicate.
+
+      # Example
+
+      ```nix
+      let
+        mySet = {
+          a = { value = 1; };
+          b = { value = 2; };
+          c = { value = 3; };
+        };
+
+        isGreaterThanOne = name: value: value.value > 1;
+
+        result = firstAttrNameMatching isGreaterThanOne mySet;
+
+      in
+        result
+      # Output: "b"
+      ```
+
+      # Type
+
+      ```
+      firstAttrNameMatching :: (String -> Any -> Bool) -> AttrSet -> String
+      ```
+
+      # Arguments
+
+      pred
+      : A function that takes an attribute name and its value and returns a boolean.
+
+      set
+      : The attribute set to filter.
+    */
+    firstAttrNameMatching =
+      pred: set:
+      pipe set [
+        (filterAttrs pred)
+        attrNames
+        head
+      ];
+  };
+}