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

let
  cfg = config.pkgInstalls;
  installScript = p:
    let
      src = pkgs.fetchurl { inherit (p) url hash; };
    in ''
      stamp="/usr/local/share/nix-pkg-stamps/${p.name}"
      want="${src}"
      if [ "$(cat "$stamp" 2>/dev/null)" != "$want" ]; then
        echo "installing ${p.name}..."
        if /usr/sbin/installer -pkg "$want" -target /; then
          mkdir -p /usr/local/share/nix-pkg-stamps
          echo "$want" > "$stamp"
        else
          echo "${p.name} install failed, skipping"
        fi
      fi
    '';
in
{
  options.pkgInstalls = lib.mkOption {
    type = lib.types.listOf (lib.types.attrsOf lib.types.str);
    default = [ ];
    description = "PKG files to install on activation";
  };

  config.system.activationScripts.postActivation.text =
    lib.concatMapStringsSep "\n" installScript cfg;
}