@@ -0,0 +1,126 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"log"
+	"os"
+	"os/signal"
+	"strings"
+	"sync"
+	"syscall"
+	"time"
+
+	"github.com/fsnotify/fsnotify"
+
+	"alin.ovh/erl/command"
+	"alin.ovh/erl/state"
+	"alin.ovh/erl/watcher"
+)
+
+var (
+	Exec = flag.String("exec", "", "command to execute on file change")
+)
+
+func Start(ctx context.Context, w watcher.Watcher, sm *state.StateMachine) {
+	var wg sync.WaitGroup
+
+	wg.Add(1)
+	go func(events <-chan watcher.Event, errors <-chan error) {
+		defer wg.Done()
+		sm.SendEvent(state.Start)
+		for {
+			select {
+			case <-ctx.Done():
+				sm.SendEvent(state.Signal)
+
+				return
+			case event, ok := <-events:
+				if !ok {
+					return
+				}
+
+				// skip if _only_ chmod
+				if event.Op == fsnotify.Chmod {
+					continue
+				}
+
+				log.Printf("event: %s %s\n", event.Name, event.Op.String())
+				if event.Op.Has(fsnotify.Create) {
+					stat, err := os.Stat(event.Name)
+					if err != nil {
+						log.Printf("Error getting file info: %v\n", err)
+
+						continue
+					}
+					if stat.IsDir() {
+						err = w.AddRecursive(event.Name)
+						if err != nil {
+							log.Printf("Error adding directory to watcher: %v\n", err)
+						}
+					}
+				}
+				if event.Op.Has(fsnotify.Remove) {
+					for _, dir := range w.WatchList() {
+						if strings.HasPrefix(dir, event.Name) {
+							err := w.Remove(dir)
+							if err != nil {
+								log.Printf("Error removing directory from watcher: %v\n", err)
+							}
+						}
+					}
+				}
+
+				sm.SendEvent(state.Restart)
+
+				time.Sleep(100 * time.Millisecond)
+
+			case err, ok := <-errors:
+				if !ok {
+					return
+				}
+				log.Printf("Error: %v\n", err)
+			}
+		}
+	}(w.Monitor())
+
+	err := w.AddRecursive(".")
+	if err != nil {
+		log.Fatalf("failed to add directory to watcher: %v", err)
+	}
+
+	<-ctx.Done()
+	log.Println("shutting down")
+
+	sm.SendEvent(state.Signal)
+
+	wg.Wait()
+}
+
+func main() {
+	log.SetFlags(log.Lmsgprefix)
+	flag.Parse()
+
+	program := *Exec
+	if program == "" {
+		log.Fatal("no command provided")
+	}
+
+	watcher, err := watcher.New()
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer watcher.Close()
+
+	ctx, cancel := signal.NotifyContext(
+		context.Background(),
+		os.Interrupt,
+		syscall.SIGHUP,
+		syscall.SIGTERM,
+	)
+	defer cancel()
+
+	cmd := command.New(program, flag.Args(), command.Options{})
+	sm := state.New(cmd, log.New(os.Stderr, "state: ", log.Lmsgprefix))
+	Start(ctx, watcher, sm)
+}