{ lib, substituteAll, ... }:

let
  inherit (builtins) length elemAt isList isString hasAttr getAttr;

  ###########################################################################
  # Helpers

  # Source: https://github.com/NixOS/nixpkgs/blob/d61bc96d16ca288c69b798b8e31eca64050098e3/lib/lists.nix
  foldr = op: nul: list:
    let
      len = length list;
      fold' = n:
        if n == len
        then nul
        else op (elemAt list n) (fold' (n + 1));
    in
    fold' 0;

  concatMap = op: list:
    let
      concat = (a: b: op a + b);
    in
    foldr concat "" list;

  ############################################################################
  # Configs

  optional = cond: val:
    let
      def =
        if isList val then [ ]
        else if isString val then ""
        else null;
    in
    if cond then val else def;

  getAttrOpt = a: s:
    if hasAttr a s then getAttr a s else null;

  #############################################################################
  # Lua

  mkLuaHeredoc = content: ''
    lua << EOF
    ${content}
    EOF
  '';

  mkLuaRc = contents: concatMap mkLuaHeredoc contents;

  ############################################################################
  # Configs

  readSubFile = src: params: builtins.readFile
    (substituteAll (params // { inherit src; }));

in
{
  inherit (lib) importJSON attrByPath;
  inherit foldr concatMap;
  inherit optional getAttrOpt;
  inherit mkLuaHeredoc mkLuaRc;
  inherit readSubFile substituteAll;
}