{
  config,
  lib,
  pkgs,
  ...
}:
let
  cfg = config.services.llama-swap;
  settingsFormat = pkgs.formats.yaml { };
  configFile =
    if cfg.configFile != null then
      cfg.configFile
    else
      settingsFormat.generate "config.yaml" cfg.settings;

  args = [
    "--listen=${cfg.listenAddress}:${toString cfg.port}"
    "--config=${configFile}"
  ]
  ++ cfg.extraArgs;
in
{
  options.services.llama-swap = {
    enable = lib.mkEnableOption "the llama-swap service";

    package = lib.mkPackageOption pkgs "llama-swap" { };

    packages = lib.mkOption {
      default = lib.optionals (cfg.configFile != null) [ pkgs.llama-cpp ];
      defaultText = lib.literalExpression ''
        lib.optionals (cfg.configFile != null) [ pkgs.llama-cpp ]
      '';
      example = lib.literalExpression ''
        [
          pkgs.llama-cpp-rocm
          pkgs.vllm
        ]
      '';
      type = lib.types.listOf lib.types.package;
      description = ''
        Packages to add to llama-swap process's PATH.
        Useful if using `configFile` instead of `settings`.
      '';
    };

    exposePackages = lib.mkOption {
      default = cfg.configFile != null;
      defaultText = lib.literalExpression "cfg.configFile != null";
      type = lib.types.bool;
      description = ''
        Whether to additionally add `packages` to user profile.
        Useful when using `configFile` instead of `settings`.
      '';
    };

    listenAddress = lib.mkOption {
      type = lib.types.str;
      default = "localhost";
      example = "0.0.0.0";
      description = ''
        Address that llama-swap listens on.
      '';
    };

    port = lib.mkOption {
      default = 8080;
      example = 11343;
      type = lib.types.port;
      description = ''
        Port that llama-swap listens on.
      '';
    };

    configFile = lib.mkOption {
      type = with lib.types; nullOr (either path str);
      default = null;
      description = ''
        Optional configuration file path to use instead of
        generating from settings
      '';
    };

    extraArgs = lib.mkOption {
      type = with lib.types; listOf str;
      default = [ ];
      description = ''
        Additional arguments to pass on llama-swap startup
      '';
    };

    settings = lib.mkOption {
      type = lib.types.submodule { freeformType = settingsFormat.type; };
      description = ''
        llama-swap configuration. Refer to the [llama-swap example configuration](https://github.com/mostlygeek/llama-swap/blob/main/config.example.yaml)
        for details on supported values.
      '';
      example = lib.literalExpression ''
        let
          llama-cpp = pkgs.llama-cpp.override { rocmSupport = true; };
          llama-server = lib.getExe' llama-cpp "llama-server";
        in
        {
          healthCheckTimeout = 60;
          models = {
            "some-model" = {
              cmd = "''${llama-server} --port ''${PORT} -m /var/lib/llama-cpp/models/some-model.gguf -ngl 0 --no-webui";
              aliases = [
                "the-best"
              ];
            };
            "other-model" = {
              proxy = "http://127.0.0.1:5555";
              cmd = "''${llama-server} --port 5555 -m /var/lib/llama-cpp/models/other-model.gguf -ngl 0 -c 4096 -np 4 --no-webui";
              concurrencyLimit = 4;
            };
          };
        };
      '';
    };
  };
  config = lib.mkIf cfg.enable {
    assertions = [
      {
        assertion = cfg.configFile != null -> (builtins.attrNames cfg.settings) == [ ];
        message = "configFile is incompatible with non-empty settings";
      }
    ];

    # untested
    systemd.user.services.llama-swap = {
      description = "Model swapping for LLaMA C++ Server (or any local OpenAPI compatible server)";

      serviceConfig = {
        Type = "exec";
        ExecStart = "${lib.getExe cfg.package} ${lib.escapeShellArgs args}";
        Restart = "on-failure";
        RestartSec = 3;

        # for GPU acceleration
        PrivateDevices = false;
      };
      path = cfg.packages;
    };

    launchd.agents.llama-swap = {
      enable = true;
      config = {
        ProgramArguments = [ (lib.getExe cfg.package) ] ++ args;
        KeepAlive = {
          Crashed = true;
          SuccessfulExit = false;
        };
        ProcessType = "Background";
        EnvironmentVariables = {
          PATH = lib.makeBinPath cfg.packages;
        };
      };
    };

    home.packages = [
      cfg.package
    ]
    ++ (lib.optionals cfg.exposePackages cfg.packages);
  };
}