{
  description = "NixOS configuration";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-25.11";
    nixpkgs-unstable.url = "github:nixos/nixpkgs/nixos-unstable";

    home-manager = {
      url = "github:nix-community/home-manager/release-25.11"; 
      # 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";
    };

    # alternative nix compiler
    lix-module = {
      url = "https://git.lix.systems/lix-project/nixos-module/archive/2.93.3-1.tar.gz";
      inputs.nixpkgs.follows = "nixpkgs";
    };

    #for device formatting
    disko = {
      url = "github:nix-community/disko/latest";
      inputs.nixpkgs.follows = "nixpkgs";
    };

    sops-nix = {
      url = "github:Mic92/sops-nix";
      inputs.nixpkgs.follows = "nixpkgs";
    };

    # for hyprvisoring
    microvm = {
      url = "github:astro/microvm.nix";
      inputs.nixpkgs.follows = "nixpkgs";
    };

    # modern window compositor
    hyprland = {
      url = "github:hyprwm/Hyprland";
      inputs.nixpkgs.follows = "nixpkgs-unstable";
    };

    nix-colors.url = "github:misterio77/nix-colors";

    #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";
    };

    modded-minecraft-servers.url = "github:mkaito/nixos-modded-minecraft-servers";

    #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:doolphin/nu_scripts";
      url = "github:nushell/nu_scripts";
      flake = false;
    };

    hugo-congo = {
      url = "https://github.com/jpanther/congo";
      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;
    };
    catppuccin-waybar = {
      url = "github:catppuccin/waybar";
      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, ... }: with inputs; 
    # packages.aarch64-linux = {
    # # packages.x86_64-linux = {
    #   aarch64-installer = nixos-generators.nixosGenerate {
    #     system = "aarch64-linux";
    #     networking.hostname = "raspi";
    #     modules = [
    #       ./modules/users/defin.nix
    #       ./modules/nixos/system-packages.nix
    #     ];
    #     format = "sd-aarch64-installer";
    #   };
    # };
    let
      inherit (self) outputs;
      lib = nixpkgs.lib // home-manager.lib;
      systems = [ "x86_64-linux" "aarch64-linux" ];
      # forAllSystems = f: lib.genAttrs systems (system: f pkgsFor.${system});
      pkgsFor = lib.genAttrs systems (system: import nixpkgs {
        inherit system;
        config.allowUnfree = true;
      });

      minimalHomeManagerSettings = [ # From github:MasterofNull/nixos config
        home-manager.nixosModules.home-manager {
          home-manager.useGlobalPkgs = true;
          home-manager.useUserPackages = true;
          home-manager.extraSpecialArgs = { inherit inputs; };
        }
        # lib.nixosSystem {
        #   modules = [
        #     ./modules/nixos/nix-common.nix
        #     ./modules/nixos/environment.nix
        #     ./modules/nixos/system-packages.nix

        #     ./modules/users/defin.nix
        #     ./modules/users/root.nix
        #   ];
        #   # # Let 'nixos-version --json' know the Git revision of this flake. (for containers?)
        #   # system.configurationRevision = nixpkgs.lib.mkIf (self ? rev) self.rev;
        #   # nix.registry.nixpkgs.flake = nixpkgs;
        # }
      ];
      # vm = lib.nixosSystem {
      #   system = "x86_64-linux";
      #   modules = [ ./default.nix ];
      # };
      # foolcreekwireless = lib.nixosSystem { # vm for website
      #   system = "x86_64-linux";
      #   modules = minimalHomeManagerSettings ++ [ ./machines/vm/foolcreekwireless
      #     home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/default.nix; }
      #   ];
      # };
    in {
      inherit lib;
      nixosModules = import ./modules/nixos;
      # homeManagerModules = import ./modules/home-manager;
      # templates = import ./templates;

      # overlays = import ./overlays { inherit inputs outputs; };
      # hydraJobs = import ./hydra.nix { inherit inputs outputs; };

      # packages = forEachSystem (pkgs: import ./pkgs { inherit pkgs; });
      # devShells = forEachSystem (pkgs: import ./shell.nix { inherit pkgs; });
      # formatter = forEachSystem (pkgs: pkgs.nixpkgs-fmt);

      # wallpapers = inherit wallpapers; #NOTE broken

      nixosConfigurations = {
        khad = lib.nixosSystem { # Main desktop
          modules = minimalHomeManagerSettings ++ [ ./machines/khad
            lix-module.nixosModules.default
            sops-nix.nixosModules.sops
            home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/home.nix; }
          ];
        };
        zenbook = lib.nixosSystem { # Personal laptop
          # specialArgs = { inherit inputs; };
          modules = minimalHomeManagerSettings ++ [ ./machines/zenbook
            lix-module.nixosModules.default
            # hyprland.homeManagerModules.default {wayland.windowManager.hyprland.enable = true;}
            home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/home.nix; }
          ];
        };

        betsy = lib.nixosSystem { # work laptop
          modules = minimalHomeManagerSettings ++ [ ./machines/betsy
            # lix-module.nixosModules.default

            home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/home.nix; }
          ];
        };
        doretta = lib.nixosSystem { # build server
          specialArgs = { inherit inputs; };
          modules = minimalHomeManagerSettings ++ [ ./machines/doretta
            lix-module.nixosModules.default
            microvm.nixosModules.host
            home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/doretta.nix; }
          ];
        };
        bosco = lib.nixosSystem { # networking server
          modules = minimalHomeManagerSettings ++ [ ./machines/bosco
            # lix-module.nixosModules.default
            home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/default.nix; }
          ];
        };
        biski = lib.nixosSystem { # another networking server, physical instead of cloud
          modules = minimalHomeManagerSettings ++ [ ./machines/biski
            disko.nixosModules.disko
            home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/default.nix; }
          ];
        };
        picast = lib.nixosSystem { # anger at chromecast
          modules = minimalHomeManagerSettings ++ [ ./machines/picast
            home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/default.nix; }
          ];
        };
        microvm-test = lib.nixosSystem { # test
          system = "x86_64-linux";
          modules = minimalHomeManagerSettings ++ [
            microvm.nixosModules.microvm
            # home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/default.nix; }
            {
              networking.hostName = "microvm-test";
              microvm.hypervisor = "qemu";
            }
          ];
        };
        foolcreek = lib.nixosSystem { # vm for website
          modules = minimalHomeManagerSettings ++ [ ./machines/vm/foolcreek
            microvm.nixosModules.microvm
            home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/default.nix; }
          ];
        };
        live = lib.nixosSystem {
          modules = minimalHomeManagerSettings ++ [
            (nixpkgs + "/nixos/modules/installer/sd-card/sd-image-aarch64-installer.nix")
            ./machines/iso/configuration.nix
            ./modules/users/defin.nix
            ./modules/nixos/system-packages.nix

            home-manager.nixosModules.home-manager { home-manager.users.defin = import ./home-manager/default.nix; }
            { nixpkgs.hostPlatform = "aarch64-linux"; }
          ];
        };
        livetest = lib.nixosSystem {
          modules = [
            (nixpkgs + "/nixos/modules/installer/cd-dvd/installation-cd-minimal.nix")
            { nixpkgs.hostPlatform = "aarch64-linux"; }
          ];
        };
        # vm declarations for nix flake check
        # foolcreek = foolcreekwireless;
      };
      # vms = { # expose the build attribute directly
      #   foolcreekwireless = foolcreekwireless.config.system.build.vm;
      # };
      homeConfigurations = { #NOTE: no worky yet
        # Standalone HM only
        # # Desktop
        # "defin@khad" = lib.homeManagerConfiguration {
        #   modules = [ ./home-manager/home.nix ];
        #   pkgs = pkgsFor.x86_64-linux;
        #   extraSpecialArgs = { inherit inputs outputs; };
        # };
        # Laptop
        "defin@nixos-zenbook" = lib.homeManagerConfiguration {
          modules = [ ./home-manager/home.nix ];
          pkgs = pkgsFor.x86_64-linux;
          extraSpecialArgs = { inherit inputs outputs; };
        };
      };
  };
}