{ lib, config, pkgs, mmdvm_host, mmdvm_firmware, ... }:
with lib;
let
  # Shorter name to access final settings a 
  # user of hello.nix module HAS ACTUALLY SET.
  # cfg is a typical convention.
  cfg = config.services.mmdvm_host;
in
{

  options.services.mmdvm_host = {
    enable = mkEnableOption "MMDVMHost service";
    
    host_package = mkOption {
      default = mmdvm_host.x86_64-linux.default;
      type = types.package;
    };

    firmware_package = mkOption {
      default = mmdvm_firmware.x86_64-linux.default;
      type = types.package;
    };
    
    user = mkOption {
      type = types.str;
      default = "afg";
    };

    group = mkOption {
      type = types.str;
      default = "afg";
    };

    config-file = mkOption {
      type = types.str;
    };

    usb-tty = mkOption {
      type = types.str;
      default = "/dev/ttyUSB0";
    };

  };


  config = mkIf cfg.enable {
    # List packages installed in system profile. To search, run:
    # $ nix search wget
    environment.systemPackages = [
      pkgs.stm32flash
      cfg.host_package
    ];

    systemd.services.mmdvm_host = {
      wantedBy = [ "multi-user.target" ];
      wants = [ "network.target" ];
      after = [ "network.target" ];
      description = "MMDVMHost service";
      serviceConfig = {
        Type = "exec";
        User = cfg.user;
        Group = cfg.group;
        Restart = "always";
        RestartSec = "3s";
        RuntimeDirectory = "MMDVMHost";
      };
      script = ''
        if [ ! -e /var/lib/mmdvm/firmware-version ]; then
          mkdir -p /var/lib/mmdvm
          touch /var/lib/mmdvm/firmware-version
        fi
        if [ "${cfg.firmware_package}" != "$(cat /var/lib/mmdvm/firmware-version)" ]; then
          ${pkgs.stm32flash}/bin/stm32flash -w ${cfg.firmware_package}/bin/mmdvm_f4.bin -i ',-dtr,-rts,dtr,,:-dtr,rts,dtr' ${cfg.usb-tty}
          echo "{cfg.firmware_package}" > /var/lib/mmdvm/firmware-version
        fi
        
        exec ${cfg.package}/bin/MMDVMHost ${cfg.config-file}
      '';
    };
  };

}