Add Pallet Watch (#25)

closes #18

Reviewed-on: http://192.168.1.227:3000/sfrembling/pallet/pulls/25
Co-authored-by: godsfryingpan <sfrembling@gmail.com>
Co-committed-by: godsfryingpan <sfrembling@gmail.com>

src/app.rs

@@ -2,6 +2,7 @@ use std::{
     env::set_current_dir,
     path::{Path, PathBuf},
     process::Command,
+    sync::{Arc, atomic::Ordering},
 };
 
 use clap::CommandFactory;
@@ -60,6 +61,14 @@ enum Subcommand {
         /// The package to be added
         package: String,
     },
+    /// Watches for source code changes and triggers a recompilation && re-run on change
+    Watch {
+        /// The build mode to use
+        mode: Option<String>,
+        /// Arguments to pass to the project binary
+        #[arg(long, short)]
+        args: Option<Vec<String>>,
+    },
 }
 
 #[derive(clap::Subcommand)]
@@ -186,10 +195,165 @@ impl App {
                     std::process::exit(1);
                 }
             }
+            Subcommand::Watch { mode, args } => {
+                if let Err(e) = watch(&mode, args) {
+                    eprintln!("Error running watch: {e}");
+                    std::process::exit(1);
+                }
+            }
         }
     }
 }
 
+fn watch(mode: &Option<String>, args: Option<Vec<String>>) -> std::io::Result<()> {
+    use std::io::Write;
+    use std::sync::Arc;
+    use std::sync::atomic::{AtomicBool, Ordering};
+
+    let mut stdout = std::io::stdout();
+
+    // enter alternate screen
+    write!(stdout, "\x1b[?1049h")?;
+    stdout.flush()?;
+
+    // set up ctrl+c handler BEFORE doing anything else
+    let running = Arc::new(AtomicBool::new(true));
+    let running_clone = running.clone();
+    ctrlc::set_handler(move || {
+        running_clone.store(false, Ordering::SeqCst);
+    })
+    .map_err(|e| std::io::Error::other(format!("{e}")))?;
+
+    let result = watch_inner(mode, args, running);
+
+    // exit alternate screen — guaranteed to run now
+    write!(stdout, "\x1b[?1049l")?;
+    stdout.flush()?;
+
+    result
+}
+
+fn watch_inner(
+    mode: &Option<String>,
+    args: Option<Vec<String>>,
+    running: Arc<std::sync::atomic::AtomicBool>,
+) -> 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 (ctrl+c to stop) — {label}",
+            "Watching".green().bold()
+        );
+        println!("{}", "─".repeat(50).dimmed());
+    };
+
+    // 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}")))?;
+
+    let mut last_build = Instant::now()
+        .checked_sub(Duration::from_secs(1))
+        .unwrap_or(Instant::now());
+
+    while running.load(Ordering::SeqCst) {
+        match rx.recv_timeout(Duration::from_millis(100)) {
+            Ok(Ok(event)) => {
+                let is_relevant = matches!(
+                    event.kind,
+                    notify::EventKind::Create(_)
+                        | notify::EventKind::Modify(_)
+                        | notify::EventKind::Remove(_)
+                );
+                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();
+
+                    // kill whatever is currently running
+                    kill_child(&mut child);
+
+                    clear();
+                    print_header("rebuilding");
+
+                    match build(mode, false) {
+                        Ok(_) => {
+                            child = run_child(mode, &args).ok();
+                        }
+                        Err(e) => {
+                            eprintln!("  {} {e}", "Error".red().bold());
+                            // child stays None until next successful build
+                        }
+                    }
+                }
+            }
+            Ok(Err(e)) => eprintln!("  {} watch error: {e}", "Error".red().bold()),
+            Err(mpsc::RecvTimeoutError::Timeout) => continue, // check running flag and loop
+            Err(mpsc::RecvTimeoutError::Disconnected) => break,
+        }
+    }
+
+    kill_child(&mut child);
+    Ok(())
+}
+
 fn add_package(package: &str) -> std::io::Result<()> {
     let status = Command::new("pkg-config")
         .arg("--exists")