refinements based on feedback

src/app.rs

@@ -205,29 +205,91 @@ impl App {
 }
 
 fn watch(mode: &Option<String>, args: Option<Vec<String>>) -> std::io::Result<()> {
+    use std::io::Write;
+
+    // save terminal state
+    let mut stdout = std::io::stdout();
+    // enter alternate screen — this is a separate terminal buffer,
+    // exiting it restores everything exactly as it was
+    write!(stdout, "\x1b[?1049h")?;
+    stdout.flush()?;
+
+    // make sure we always restore the terminal, even on panic
+    let result = watch_inner(mode, args);
+
+    // exit alternate screen
+    write!(stdout, "\x1b[?1049l")?;
+    stdout.flush()?;
+
+    result
+}
+
+fn watch_inner(mode: &Option<String>, args: Option<Vec<String>>) -> std::io::Result<()> {
     use notify::{Event, RecursiveMode, Watcher, recommended_watcher};
+    use std::io::Write;
     use std::sync::mpsc;
     use std::time::{Duration, Instant};
 
+    let clear = || {
+        let mut stdout = std::io::stdout();
+        write!(stdout, "\x1b[2J\x1b[H").ok();
+        stdout.flush().ok();
+    };
+
+    let print_header = |label: &str| {
         println!(
-        "  {} project for changes (ctrl+c to stop)",
+            "  {} project (ctrl+c to stop) — {label}",
             "Watching".green().bold()
         );
+        println!("{}", "─".repeat(50).dimmed());
+    };
 
-    // do an initial build+run before watching
-    build(mode, false)?;
-    run(mode, args.clone())?;
+    // track the running child process
+    let mut child: Option<std::process::Child> = None;
+
+    let kill_child = |child: &mut Option<std::process::Child>| {
+        if let Some(c) = child {
+            c.kill().ok();
+            c.wait().ok();
+        }
+        *child = None;
+    };
+
+    let run_child = |mode: &Option<String>,
+                     args: &Option<Vec<String>>|
+     -> std::io::Result<std::process::Child> {
+        let conf = get_config().ok_or(std::io::Error::new(
+            std::io::ErrorKind::NotFound,
+            "no Pallet.toml found",
+        ))?;
+        let build_config = conf.get_or_default(mode).ok_or(std::io::Error::new(
+            std::io::ErrorKind::NotFound,
+            "build layout not found",
+        ))?;
+        let mut command = Command::new(format!("target/{}/{}", build_config.name, conf.name));
+        if let Some(a) = args {
+            for arg in a {
+                command.arg(arg);
+            }
+        }
+        command
+            .spawn()
+            .map_err(|e| std::io::Error::other(format!("{e}")))
+    };
+
+    // initial build + run
+    clear();
+    print_header("starting");
+    if build(mode, false).is_ok() {
+        child = run_child(mode, &args).ok();
+    }
 
     let (tx, rx) = mpsc::channel::<notify::Result<Event>>();
-
     let mut watcher = recommended_watcher(tx).map_err(|e| std::io::Error::other(format!("{e}")))?;
-
     watcher
         .watch(Path::new("src"), RecursiveMode::Recursive)
         .map_err(|e| std::io::Error::other(format!("{e}")))?;
 
-    // debounce — ignore events within 500ms of the last one
-    // this prevents double-triggers from editors that write files in multiple steps
     let mut last_build = Instant::now()
         .checked_sub(Duration::from_secs(1))
         .unwrap_or(Instant::now());
@@ -235,37 +297,37 @@ fn watch(mode: &Option<String>, args: Option<Vec<String>>) -> std::io::Result<()
     loop {
         match rx.recv() {
             Ok(Ok(event)) => {
-                // only care about actual file modifications
                 let is_relevant = matches!(
                     event.kind,
                     notify::EventKind::Create(_)
                         | notify::EventKind::Modify(_)
                         | notify::EventKind::Remove(_)
                 );
-
-                // only care about .c and .h files
                 let affects_source = event.paths.iter().any(|p| {
                     matches!(
                         p.extension().and_then(|e| e.to_str()),
                         Some("c") | Some("h")
                     )
                 });
-
                 let debounced = last_build.elapsed() > Duration::from_millis(500);
 
                 if is_relevant && affects_source && debounced {
                     last_build = Instant::now();
-                    println!(
-                        "\n  {} changes detected, rebuilding...",
-                        "Watch".green().bold()
-                    );
-                    if let Err(e) = build(mode, false) {
-                        eprintln!("  {} {e}", "Error".red().bold());
-                        // don't exit — keep watching even if build fails
-                        continue;
+
+                    // kill whatever is currently running
+                    kill_child(&mut child);
+
+                    clear();
+                    print_header("rebuilding");
+
+                    match build(mode, false) {
+                        Ok(_) => {
+                            child = run_child(mode, &args).ok();
                         }
-                    if let Err(e) = run(mode, args.clone()) {
+                        Err(e) => {
                             eprintln!("  {} {e}", "Error".red().bold());
+                            // child stays None until next successful build
+                        }
                     }
                 }
             }
@@ -277,6 +339,7 @@ fn watch(mode: &Option<String>, args: Option<Vec<String>>) -> std::io::Result<()
         }
     }
 
+    kill_child(&mut child);
     Ok(())
 }