{
  inputs = {
    nixpkgs.url = github:NixOS/nixpkgs/nixos-22.11;
    nixpkgs-unstable.url = github:NixOS/nixpkgs/nixos-unstable;

    home-manager = {
      url = github:nix-community/home-manager/release-22.11;
      inputs.nixpkgs.follows = "nixpkgs";
    };

  };

  outputs = inputs@{ self, nixpkgs, nixpkgs-unstable, home-manager, ... }:
    let
      user = "mandlm";
      theme = "dark";       # dark or light

      overlays = {
        unstable-packages = _final: _prev: {
          unstable = import nixpkgs-unstable {
            system = "x86_64-linux";
            config.allowUnfree = true;
          };
        };
      };

      nixpkgs_config = {
        overlays = [
          overlays.unstable-packages
        ];
        config = {
          allowUnfree = true;
          allowUnfreePredicate = (_: true);
        };
      };
    in
    {

      nixosConfigurations = {
        nixos-vm = nixpkgs.lib.nixosSystem {
          system = "x86_64-linux";
          modules = [
            ./configuration.nix
            ./users.nix
            ./machines/nixos-vm/configuration.nix
            ./machines/nixos-vm/hardware-configuration.nix

            home-manager.nixosModules.home-manager
            {
              home-manager.extraSpecialArgs = { inherit user theme; };
              home-manager.users.${user} = {
                imports = [ ./home-${user}.nix ];
                nixpkgs = nixpkgs_config;
              };
            }
          ];
        };

        apache = nixpkgs.lib.nixosSystem {
          system = "x86_64-linux";
          modules = [
            ./configuration.nix
            ./users.nix
            ./machines/apache/configuration.nix
            ./machines/apache/hardware-configuration.nix

            home-manager.nixosModules.home-manager
            {
              home-manager.extraSpecialArgs = { inherit user theme; };
              home-manager.users.${user} = {
                imports = [
                  ./home-${user}.nix
                  ./machines/apache/home-${user}.nix
                ];
                nixpkgs = nixpkgs_config;
              };
            }
          ];
        };

        p330 = nixpkgs.lib.nixosSystem {
          system = "x86_64-linux";
          modules = [
            ./configuration.nix
            ./users.nix
            ./machines/p330/configuration.nix
            ./machines/p330/hardware-configuration.nix

            home-manager.nixosModules.home-manager
            {
              home-manager.extraSpecialArgs = { inherit user theme; };
              home-manager.users.${user} = {
                imports = [
                  ./home-${user}.nix
                  ./machines/p330/home-${user}.nix
                ];
                nixpkgs = nixpkgs_config;
              };
            }
          ];
        };

        yoga = nixpkgs.lib.nixosSystem {
          system = "x86_64-linux";
          modules = [
            ./configuration.nix
            ./users.nix
            ./machines/yoga/configuration.nix
            ./machines/yoga/hardware-configuration.nix

            home-manager.nixosModules.home-manager
            {
              home-manager.extraSpecialArgs = { inherit user theme; };
              home-manager.users.${user} = {
                imports = [
                  ./home-${user}.nix
                  ./machines/yoga/home-${user}.nix
                ];
                nixpkgs = nixpkgs_config;
              };
            }
          ];
        };
      };
    };
}