puzzlevision/modules/flake/lib.nix

{
  lib,
  puzzlelib,
  ...
}: 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);
in {
  # Add lib.${namespace} attribute to module arguments, for easy access.
  # Additionally, pass on dirToAttrSet method on lib.${namespace} for reusability in other modules.
  _module.args = {
    puzzlelib = dirToAttrSet ../../lib {inherit lib puzzlelib;} // {inherit dirToAttrSet dirToModuleList filesystemEntityToList filesystemEntityToAttrSet;};
  };
}