{
  description = "Nostr relay Prometheus exporter";

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

  outputs = { self, nixpkgs }:
    let
      inherit (nixpkgs.lib) genAttrs;
      systems = [ "x86_64-linux" "aarch64-linux" ];
      forAllSystems = genAttrs systems;

      mkPackage = pkgs:
        let
          pname = "relay-exporter";
          version = "0.1.0";
          src = pkgs.lib.cleanSourceWith {
            src = ./.;
            filter = path: type:
              !(pkgs.lib.hasInfix "/.git/" path)
              && !(pkgs.lib.hasInfix "/node_modules/" path)
              && !(pkgs.lib.hasInfix "/dist/" path);
          };
        in
        pkgs.stdenv.mkDerivation {
          inherit pname version;
          inherit src;

          nativeBuildInputs = [
            pkgs.nodejs_22
            pkgs.pnpm.configHook
            pkgs.makeWrapper
          ];

          pnpmDeps = pkgs.pnpm.fetchDeps {
            inherit pname version src;
            fetcherVersion = 1;
            hash = "sha256-rZhEXQcRPS5pHdXNfrYeTI3zxkqtJjcyaGgrmzwFaHA=";
          };

          buildPhase = ''
            runHook preBuild
            pnpm run build
            runHook postBuild
          '';

          installPhase = ''
            runHook preInstall
            mkdir -p $out/app $out/bin
            cp -r dist package.json node_modules $out/app/
            makeWrapper ${pkgs.nodejs_22}/bin/node $out/bin/relay-exporter \
              --set NODE_ENV production \
              --add-flags "$out/app/dist/index.js"
            runHook postInstall
          '';

          meta = {
            description = "Prometheus exporter for Nostr relay health checks";
            mainProgram = "relay-exporter";
            license = pkgs.lib.licenses.mit;
            platforms = pkgs.lib.platforms.linux;
          };
        };
    in
    rec {
      packages = forAllSystems (system:
        let
          pkgs = import nixpkgs { inherit system; };
          pkg = mkPackage pkgs;
        in
        {
          relay-exporter = pkg;
          default = pkg;
        });

      devShells = forAllSystems (system:
        let
          pkgs = import nixpkgs { inherit system; };
        in
        {
          default = pkgs.mkShell {
            packages = [
              pkgs.nodejs_22
              pkgs.pnpm_10
            ];
          };
        });

      overlays.default = final: prev: {
        relay-exporter = self.packages.${prev.stdenv.hostPlatform.system}.relay-exporter;
      };

      nixosModules.default =
        { config, lib, pkgs, ... }:
        let
          inherit (lib) mkEnableOption mkIf mkOption types;
          cfg = config.services.relay-exporter;
          system = pkgs.stdenv.hostPlatform.system;
          defaultPackage = self.packages.${system}.relay-exporter;
        in
        {
          options.services.relay-exporter = {
            enable = mkEnableOption "relay-exporter service";

            package = mkOption {
              type = types.package;
              default = defaultPackage;
              defaultText = "self.packages.${system}.relay-exporter";
              description = "Derivation that provides relay-exporter.";
            };

            port = mkOption {
              type = types.port;
              default = 9464;
              description = "HTTP listen port for relay-exporter.";
            };

            listenAddr = mkOption {
              type = types.str;
              default = "0.0.0.0";
              description = "Listen address for relay-exporter.";
            };

            stateDirectory = mkOption {
              type = types.str;
              default = "relay-exporter";
              description = "Name of the state directory managed by systemd.";
            };

            environment = mkOption {
              type = types.attrsOf types.str;
              default = { };
              description = "Additional environment variables for relay-exporter.";
            };

            environmentFile = mkOption {
              type = types.nullOr types.path;
              default = null;
              description = "Optional environment file consumed by systemd.";
            };
          };

          config = mkIf cfg.enable {
            systemd.services.relay-exporter = {
              description = "Nostr relay Prometheus exporter";
              wantedBy = [ "multi-user.target" ];
              after = [ "network-online.target" ];
              wants = [ "network-online.target" ];

              environment = {
                NODE_ENV = "production";
                PORT = builtins.toString cfg.port;
                LISTEN_ADDR = cfg.listenAddr;
              } // cfg.environment;

              serviceConfig =
                {
                  Type = "simple";
                  ExecStart = "${cfg.package}/bin/relay-exporter";
                  DynamicUser = true;
                  StateDirectory = cfg.stateDirectory;
                  WorkingDirectory = "/var/lib/${cfg.stateDirectory}";
                  Restart = "on-failure";
                  RestartSec = 3;
                }
                // lib.optionalAttrs (cfg.environmentFile != null) {
                  EnvironmentFile = cfg.environmentFile;
                };
            };
          };
        };
    };
}