{
  description = "BTCPay server, NBXplorer, Bitcoin Core, etc. as a NixOS system/container image";

  inputs = {
    nix-bitcoin.url = "github:fort-nix/nix-bitcoin/release";
    nixpkgs.follows = "nix-bitcoin/nixpkgs";
    nixos-generators.url = "github:nix-community/nixos-generators";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, nix-bitcoin, nixos-generators, flake-utils, ... }:
    let
      system = "x86_64-linux";
      pkgs = import nixpkgs { inherit system; };
      modules = [
        nix-bitcoin.nixosModules.default
        ./nix/modules/bitcoind
        ./nix/modules/nbxplorer
        ./nix/modules/btcpay
      ];
    in {
      # Top-level nixosConfigurations for proper nixos-rebuild support
      nixosConfigurations.btc-pay-server = nixpkgs.lib.nixosSystem {
        system = "x86_64-linux";
        modules = modules ++ [
          ({ config, ... }: {
            boot.isContainer = true;
            system.stateVersion = "25.05";
            services.btcpay-full.enable = true;

            users.users.root.openssh.authorizedKeys.keys = [
              "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIAaV7JtUWkWrjo5FfCcpTCCEY/OJ+T1mJOLbe4avg0XH sysadmin@skrybit.io"
            ];

            services.openssh = {
              enable = true;
              settings = {
                PermitRootLogin = "prohibit-password";
                PasswordAuthentication = false;
              };
            };
          })
          self.nixosModules.btcpay-server
        ];
      };

      # devShells and other per-system outputs, if desired
      devShells = flake-utils.lib.eachDefaultSystem (system:
        let
          pkgs = import nixpkgs { inherit system; };
        in {
          default = pkgs.mkShell {
            buildInputs = [
              nixos-generators.packages.${system}.nixos-generate
              pkgs.just
            ];
            shellHook = ''
              echo "💚 Devshell ready: nixos-generate, just available."
            '';
          };
        }
      );
    };
}