watcher: Add file deleted by accident

See #7972

watcher/batcher.go

@@ -0,0 +1,73 @@
+// Copyright 2020 The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package watcher
+
+import (
+	"time"
+
+	"github.com/fsnotify/fsnotify"
+)
+
+// Batcher batches file watch events in a given interval.
+type Batcher struct {
+	*fsnotify.Watcher
+	interval time.Duration
+	done     chan struct{}
+
+	Events chan []fsnotify.Event // Events are returned on this channel
+}
+
+// New creates and starts a Batcher with the given time interval.
+func New(interval time.Duration) (*Batcher, error) {
+	watcher, err := fsnotify.NewWatcher()
+
+	batcher := &Batcher{}
+	batcher.Watcher = watcher
+	batcher.interval = interval
+	batcher.done = make(chan struct{}, 1)
+	batcher.Events = make(chan []fsnotify.Event, 1)
+
+	if err == nil {
+		go batcher.run()
+	}
+
+	return batcher, err
+}
+
+func (b *Batcher) run() {
+	tick := time.Tick(b.interval)
+	evs := make([]fsnotify.Event, 0)
+OuterLoop:
+	for {
+		select {
+		case ev := <-b.Watcher.Events:
+			evs = append(evs, ev)
+		case <-tick:
+			if len(evs) == 0 {
+				continue
+			}
+			b.Events <- evs
+			evs = make([]fsnotify.Event, 0)
+		case <-b.done:
+			break OuterLoop
+		}
+	}
+	close(b.done)
+}
+
+// Close stops the watching of the files.
+func (b *Batcher) Close() {
+	b.done <- struct{}{}
+	b.Watcher.Close()
+}