{ config, lib, pkgs, ... }:

{
  # auto upgrade nix package and the daemon service.
  services.nix-daemon.enable = true;

  # enable the linux builder
  nix.linux-builder = {
    enable = true;
    package = pkgs.darwin.linux-builder-x86_64;
    ephemeral = true;
    maxJobs = 4;
    config = {
      virtualisation = {
        darwin-builder = {
          diskSize = 40 * 1024;
          memorySize = 8 * 1024;
        };
        cores = 6;
      };
    };
  };

  # enable trusted users
  nix.settings.trusted-users = [ "@admin" ];

  # nix auto garbage collection
  nix.gc = {
    automatic = true;
    interval = { Weekday = 0; Hour = 0; Minute = 0; };
    options = "--delete-older-than 7d";
  };

  # make nix applications use alias instead of symlinks for compatability
  system.activationScripts.applications.text = let
    env = pkgs.buildEnv {
      name = "system-applications";
      paths = config.environment.systemPackages;
      pathsToLink = "/Applications";
    };
  in
    pkgs.lib.mkForce ''
    # Set up applications.
    echo "setting up /Applications..." >&2
    rm -rf /Applications/Nix\ Apps
    mkdir -p /Applications/Nix\ Apps
    find ${env}/Applications -maxdepth 1 -type l -exec readlink '{}' + |
    while read -r src; do
      app_name=$(basename "$src")
      echo "copying $src" >&2
      ${pkgs.mkalias}/bin/mkalias "$src" "/Applications/Nix Apps/$app_name"
    done
        '';

  # changing this might break
  system.stateVersion = 5;
}