Refactor Tagger package. Add fsNotify Service

internal/util/fswatcher.go

@@ -0,0 +1,73 @@
+// Copyright (C) 2023 NHR@FAU, University Erlangen-Nuremberg.
+// All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+package util
+
+import (
+	"sync"
+
+	"github.com/ClusterCockpit/cc-backend/pkg/log"
+	"github.com/fsnotify/fsnotify"
+)
+
+type Listener interface {
+	EventCallback()
+	EventMatch(event string) bool
+}
+
+var (
+	initOnce  sync.Once
+	w         *fsnotify.Watcher
+	listeners []Listener
+)
+
+func AddListener(path string, l Listener) {
+	var err error
+
+	initOnce.Do(func() {
+		var err error
+		w, err = fsnotify.NewWatcher()
+		if err != nil {
+			log.Error("creating a new watcher: %w", err)
+		}
+		listeners = make([]Listener, 0)
+
+		go watchLoop(w)
+	})
+
+	listeners = append(listeners, l)
+	err = w.Add(path)
+	if err != nil {
+		log.Warnf("%q: %s", path, err)
+	}
+}
+
+func FsWatcherShutdown() {
+	w.Close()
+}
+
+func watchLoop(w *fsnotify.Watcher) {
+	for {
+		select {
+		// Read from Errors.
+		case err, ok := <-w.Errors:
+			if !ok { // Channel was closed (i.e. Watcher.Close() was called).
+				return
+			}
+			log.Errorf("watch event loop: %s", err)
+		// Read from Events.
+		case e, ok := <-w.Events:
+			if !ok { // Channel was closed (i.e. Watcher.Close() was called).
+				return
+			}
+
+			log.Infof("Event %s", e)
+			for _, l := range listeners {
+				if l.EventMatch(e.String()) {
+					l.EventCallback()
+				}
+			}
+		}
+	}
+}