Make subcommand optional

src/args.rs

@@ -12,7 +12,7 @@ pub struct EnvOpt {
     )]
     pub config: PathBuf,
     #[argh(subcommand)]
-    pub subcommand: Subcommand,
+    pub subcommand: Option<Subcommand>,
 }
 
 #[derive(FromArgs)]

src/cmd.rs

@@ -6,7 +6,7 @@ use thingy_lib::chrono::NaiveDateTime;
 use thingy_lib::{try_get_datetime, Config, MessagedError};
 
 pub fn from_env(env: EnvOpt) -> Result<(), GenericError> {
-    match env.subcommand {
+    match env.subcommand.unwrap() {
         Subcommand::Between(opt) => {
             let config = Config::from_path(&env.config)?;
             let mut api = API::new(config.clone());

src/main.rs

@@ -12,8 +12,12 @@ use thingy_lib::Config;
 
 fn main() {
     let env: EnvOpt = argh::from_env();
+    if env.subcommand.is_some() {
         if let Err(e) = cmd::from_env(env) {
             eprintln!("Critical Error: {}", e);
             std::process::exit(1);
         }
+    } else {
+        println!("Open nwg UI instead");
+    }
 }