repl.nix

{ flakePath ? null
, hostnamePath ? "/etc/hostname"
, registryPath ? /etc/nix/registry.json
}:

let
  inherit (builtins)
    getFlake head match currentSystem readFile pathExists filter fromJSON;

  selfFlake =
    if pathExists registryPath then
      filter (it: it.from.id == "self") (fromJSON (readFile registryPath)).flakes
    else
      [ ];

  flakePath' = toString (if flakePath != null then
    flakePath
  else if selfFlake != [ ] then
    (head selfFlake).to.path
  else
    "/etc/nixos");

  flake = if pathExists flakePath' then getFlake flakePath' else { };
  hostname =
    if pathExists hostnamePath then
      head
        (match ''
          ([a-zA-Z0-9\-]+)
        ''
          (readFile hostnamePath))
    else
      "";

  nixpkgsFromInputsPath = flake.inputs.nixpkgs.outPath or "";
  nixpkgs =
    flake.pkgs.${currentSystem}.nixpkgs or (if nixpkgsFromInputsPath != "" then
      import nixpkgsFromInputsPath { }
    else
      { });

  nixpkgsOutput =
    (removeAttrs (nixpkgs // nixpkgs.lib or { }) [ "options" "config" ]);
in
{
  inherit flake;
} // flake // builtins // (flake.nixosConfigurations or { })
// (flake.darwinConfigurations or { })
// flake.nixosConfigurations.${hostname} or { }
// flake.darwinConfigurations.${hostname} or { } // nixpkgsOutput // {
  getFlake = path: getFlake (toString path);
}