puzzlevision/modules/flake/lib.nix

{
  lib,
  self,
  ...
}:
let
  # Utility function to read a directory and return its contents.
  readDirectory = directory: builtins.readDir directory;

  # Utility function to handle each filesystem entity (file or directory).
  filesystemEntityToAttrSet =
    directory: importArgs: name: type:
    if type == "directory" then
      dirToAttrSet "${directory}/${name}" importArgs
    else if name == "default.nix" then
      import "${directory}/${name}" importArgs
    else
      { };

  filesystemEntityToList =
    directory: name: type:
    if type == "directory" then
      dirToModuleList "${directory}/${name}"
    else if name == "default.nix" then
      [ "${directory}/${name}" ]
    else
      [ ];

  dirToModuleList =
    directory:
    let
      readDir = readDirectory directory;
    in
    builtins.foldl' (
      acc: name: acc ++ (filesystemEntityToList directory name (builtins.getAttr name readDir))
    ) [ ] (builtins.attrNames readDir);

  # Utility function to recursively load modules from a directory.
  dirToAttrSet =
    directory: importArgs:
    let
      # Read provided directory only once at the very start and save the result.
      readDir = readDirectory directory;
    in
    # Iterate over the attr names of a readDir operation.
    builtins.foldl' (
      acc: name:
      # Merge outputs of handling a filesystem entity (file or directory) into accumulator.
      # Files return attribute sets with their resulting expressions, directories return the result of multiple file handling operations.
      acc // (filesystemEntityToAttrSet directory importArgs name (builtins.getAttr name readDir))
    ) { } (builtins.attrNames readDir);

  puzzlelib = dirToAttrSet ../../lib { inherit lib self; } // {
    inherit
      dirToAttrSet
      dirToModuleList
      filesystemEntityToList
      filesystemEntityToAttrSet
      ;
  };
in
{
  # Expose custom library on flake "lib" output
  flake.lib = puzzlelib;
}