{
  description = "NixOS configuration";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-23.05";
    nixpkgs-unstable.url = "github:nixos/nixpkgs/nixos-unstable";

    home-manager = {
      url = "github:nix-community/home-manager/release-23.05"; 
      # The `follows` keyword in inputs is used for inheritance.
      # Here, `inputs.nixpkgs` of home-manager isn't kept consistent with the `inputs.nixpkgs` of the current flake,
      # to not avoid problems caused by different versions of nixpkgs dependencies.
      inputs.nixpkgs.follows = "nixpkgs-unstable";
    };

    # modern window compositor
    hyprland.url = "github:hyprwm/Hyprland";

    #community wayland nixpkgs
    # nixpkgs-wayland.url = "github:nix-community/nixpkgs-wayland";
    # anyrun - a wayland launcher
    # anyrun = {
    #   url = "github:Kirottu/anyrun";
    #   inputs.nixpkgs.follows = "nixpkgs-unstable";
    # };

    # # generate iso/qcow2/docker/... image from nixos configuration
    # nixos-generators = {
    #   url = "github:nix-community/nixos-generators";
    #   inputs.nixpkgs.follows = "nixpkgs";
    # };

    #secrets management, lock with git commit at 20xx/x/xx
    #.........

    ##################### Some non-flake repositories #########################################

    # # AstroNvim is an aesthetic and feature-ruch neovim config.
    # astronvim = {
    #   url = "github:AstroNvim/AstroVnim/v3.36.0";
    #   flake = false;
    # };

    # # useful nushell scripts, such as auto_completion
    # nushell-scripts = {
    #   url = "github:nushell/nu_scripts"
    #   flake = false;
    # };

    # ryan4yin wallpapers
    wallpapers = {
      url = "github:ryan4yin/wallpapers";
      flake = false;
    };

    # # nur-ryan4yin = {
    #   url = "github:ryan4yin/nur-packages";
    #   # inputs.nixpkgs.follows "nixpkgs";
    # };

    # # riscv64 SBCs
    # nixos-licheepi4a.url = "github:ryan4yin/nixos-licheepi4a";
    # # nixos-jh7110.url = "github:ryan4yin/nixos-jh7110";

    # aarch64 SBCs
    # nixos-rk3588.url = "github:ryan4yin/nixos-rk3588";

    ############# Personal repositories ########################################

    # # my private secrets, it's a private repository, you need to replace it with your own.
    # # use ssh protocol to authenticate via ssh-agent/ssh-key, and shallow clone to save time
    # mysecrets = {
    #   url = "";
    #   flake = false;
    # };

    ##################### Color Schemes #######################################

    #color scheme -catppuccin
    catppuccin-btop = {
      url = "github:catppuccin/btop";
      flake = false;
    };
    catppuccin-bat = {
      url = "github:catppuccin/bat";
      flake = false;
    };
    catppuccin-alacritty = {
      url = "github:catppuccin/alacritty";
      flake = false;
    };
    catppuccin-helix = {
      url = "github:catppuccin/helix";
      flake = false;
    };
    catppuccin-starship = {
      url = "github:catppuccin/starship";
      flake = false;
    };
    catppuccin-hyprland = {
      url = "github:catppuccin/hyprland";
      flake = false;
    };


    # # the nixConfig here only affects the flake inself, not the system configuration!
    # nixConfig = {
    #   experimental-features = ["nix-command" "flakes"];

    #   substituters = [
    #     #my own cache server
    #     "url-here"
    #     "https://cache.nixos.org"
    #     "https://hyprland.cachix.org"
    #   ];

    #   # nix community's cache server
    #   extra-substituters = [
    #     "https://nix-community.cachix.org"
    #     "https://nixpkgs-wayland.cachix.org"
    #   ];
    #   extra-trusted-public-keys = [
    #     "keys here"
    #   ];
    # };
    
  };

  # outputs = inputs@{ self, nixpkgs, nixpkgs-unstable, home-manager, hyprland, ... }: {
  outputs = inputs@{ self, nixpkgs, nixpkgs-unstable, home-manager, wallpapers, catppuccin-btop, catppuccin-bat, catppuccin-alacritty, catppuccin-starship, catppuccin-hyprland, ... }: {

    nixosConfigurations = {

      nixos-zenbook = nixpkgs.lib.nixosSystem {
        # inherit system;
        modules = [
          ./machines/zenbook/configuration.nix
          
          ./machines/zenbook/hardware-configuration.nix

          # Default users
          ./modules/user-profiles/defin.nix
          ./modules/user-profiles/root.nix

          home-manager.nixosModules.home-manager {

            home-manager.useGlobalPkgs = true;
            home-manager.useUserPackages = true;
            home-manager.users.defin = import ./home-manager/home.nix;

            # Optionally, use home-manager.extraSpecialArgs to pass
            # arguments to home.nix
          }

          # hyprland.homeManagerModules.default {wayland.windowManager.hyprland.enable = true;}
          ./modules/hyprland.nix

          ./modules/bluetooth.nix
          ./modules/environment.nix
          ./modules/kde-connect.nix
          ./modules/nix-common.nix
          ./modules/services.nix
          ./modules/steam.nix
          ./modules/sway.nix
          ./modules/system-packages.nix

          # ./home-manager/home.nix

          # # Let 'nixos-version --json' know the Git revision of this flake.
          # system.configurationRevision = nixpkgs.lib.mkIf (self ? rev) self.rev;
          # nix.registry.nixpkgs.flake = nixpkgs;
        ];
      };

      khad = nixpkgs.lib.nixosSystem {
        modules = [
          ./machines/khad/configuration.nix

          ./machines/khad/hardware-configuration.nix

          ./modules/user-profiles/defin.nix

          home-manager.nixosModules.home-manager {
            home-manager.useGlobalPkgs = true;
            home-manager.useUserPackages = true;
            home-manager.users.defin = import ./home-manager/home.nix;
          }
          ./modules/hyprland.nix

          ./modules/bluetooth.nix
          ./modules/environment.nix
          ./modules/kde-connect.nix
          ./modules/nix-common.nix
          ./modules/services.nix
          ./modules/steam.nix
          ./modules/sway.nix
          ./modules/system-packages.nix
        ];
      };
    };
  };
}