implement watch mode

src/main.rs

@@ -1,18 +1,48 @@
-use anyhow::{anyhow, Result};
+use std::path::PathBuf;
+use std::sync::mpsc;
+use std::time::Duration;
+
+use anyhow::{bail, Result};
 use microw8::MicroW8;
+use notify::{DebouncedEvent, Watcher};
+use pico_args::Arguments;
 
 mod microw8;
 
 fn main() -> Result<()> {
-    let filename = std::env::args()
-        .nth(1)
-        .ok_or_else(|| anyhow!("Missing .uw8 file path"))?;
+    let mut args = Arguments::from_env();
+
+    let watch_mode = args.contains(["-w", "--watch"]);
+
+    let filename = args.free_from_os_str::<PathBuf, bool>(|s| Ok(s.into()))?;
 
     let mut uw8 = MicroW8::new()?;
 
-    uw8.load_from_file(filename)?;
+    let (tx, rx) = mpsc::channel();
+    let mut watcher = notify::watcher(tx, Duration::from_millis(100))?;
+
+    if watch_mode {
+        watcher.watch(&filename, notify::RecursiveMode::NonRecursive)?;
+    }
+
+    if let Err(err) = uw8.load_from_file(&filename) {
+        if !watch_mode {
+            return Err(err);
+        }
+        eprintln!("Load error: {}", err);
+    }
 
     while uw8.is_open() {
+        match rx.try_recv() {
+            Ok(DebouncedEvent::Create(_) | DebouncedEvent::Write(_)) => {
+                if let Err(err) = uw8.load_from_file(&filename) {
+                    eprintln!("Load error: {}", err)
+                }
+            }
+            Err(mpsc::TryRecvError::Disconnected) => bail!("File watcher disconnected"),
+            _ => (),
+        }
+
         uw8.run_frame()?;
     }