feat: implement and test tailer file component

vendor/github.com/nxadm/tail/watch/filechanges.go

@@ -0,0 +1,37 @@
+// Copyright (c) 2019 FOSS contributors of https://github.com/nxadm/tail
+package watch
+
+type FileChanges struct {
+	Modified  chan bool // Channel to get notified of modifications
+	Truncated chan bool // Channel to get notified of truncations
+	Deleted   chan bool // Channel to get notified of deletions/renames
+}
+
+func NewFileChanges() *FileChanges {
+	return &FileChanges{
+		make(chan bool, 1), make(chan bool, 1), make(chan bool, 1)}
+}
+
+func (fc *FileChanges) NotifyModified() {
+	sendOnlyIfEmpty(fc.Modified)
+}
+
+func (fc *FileChanges) NotifyTruncated() {
+	sendOnlyIfEmpty(fc.Truncated)
+}
+
+func (fc *FileChanges) NotifyDeleted() {
+	sendOnlyIfEmpty(fc.Deleted)
+}
+
+// sendOnlyIfEmpty sends on a bool channel only if the channel has no
+// backlog to be read by other goroutines. This concurrency pattern
+// can be used to notify other goroutines if and only if they are
+// looking for it (i.e., subsequent notifications can be compressed
+// into one).
+func sendOnlyIfEmpty(ch chan bool) {
+	select {
+	case ch <- true:
+	default:
+	}
+}