{ nixpkgs, pkgs, system, inputs }:
with pkgs.lib; {
  substitute = runCommand: name: inFile: vars: 
    runCommand name {}
      (let
        varsStr = pkgs.lib.mapAttrsToList
          (name: value: ''--subst-var-by "${name}" "${value}"'')
          vars;
      in
        ''
          substitute ${inFile} $out \
          ${builtins.concatStringsSep " " varsStr}
        '');
  flakes = path: modules: genAttrs modules (module:
    let
      self = (import (path + "/${module}/flake.nix")).outputs (inputs // { inherit self; });
    in
      self
  );
  dockerImages = pkgs: path: modules: genAttrs modules (module:
    import (path + "/${module}") ({ inherit pkgs system; } // inputs)
  );
  pkgsWithFlakes = flakes: import nixpkgs
    {
      inherit system;
      overlays = builtins.concatLists (mapAttrsToList (_: flake:
        if builtins.hasAttr "overlay" flake then
          [ flake.overlay ]
        else
          []
      ) flakes);
    };
}