OliveTin/internal/filehelper/file_change_notify.go

package filehelper

import (
	"github.com/fsnotify/fsnotify"
	log "github.com/sirupsen/logrus"
	"path/filepath"
	"time"

	"sync"
)

var (
	debounceWriteLog map[string]*FsNotifyLogEntry

	debounceWriteLogMutex = sync.Mutex{}
)

func init() {
	debounceWriteLog = make(map[string]*FsNotifyLogEntry)
}

type FsNotifyLogEntry struct {
	callbackWrapper  *time.Timer
	callbackComplete bool
}

const (
	debounceDelay = 300 * time.Millisecond
)

type watchContext struct {
	filename        string
	filedir         string
	callback        func(filename string)
	interestedEvent fsnotify.Op
	event           *fsnotify.Event
}

func WatchDirectoryCreate(fullpath string, callback func(filename string)) {
	watchPath(&watchContext{
		filedir:         fullpath,
		filename:        "",
		callback:        callback,
		interestedEvent: fsnotify.Create,
	})
}

func WatchDirectoryWrite(fullpath string, callback func(filename string)) {
	watchPath(&watchContext{
		filedir:         fullpath,
		filename:        "",
		callback:        callback,
		interestedEvent: fsnotify.Write,
	})
}

func WatchFileWrite(fullpath string, callback func(filename string)) {
	filename := filepath.Base(fullpath)
	filedir := filepath.Dir(fullpath)

	watchPath(&watchContext{
		filedir:         filedir,
		filename:        filename,
		callback:        callback,
		interestedEvent: fsnotify.Write,
	})
}

func watchPath(ctx *watchContext) {
	watcher, err := fsnotify.NewWatcher()

	if err != nil {
		log.Errorf("Could not watch for files being created: %v", err)
		return
	}

	defer watcher.Close()

	done := make(chan bool)

	go func() {
		for {
			processEvent(ctx, watcher)
		}
	}()

	err = watcher.Add(ctx.filedir)

	if err != nil {
		log.Errorf("Could not create watcher: %v", err)
	}

	<-done
}

func processEvent(ctx *watchContext, watcher *fsnotify.Watcher) {
	select {
	case event, ok := <-watcher.Events:
		ctx.event = &event

		if !consumeEvent(ok, ctx) {
			return
		}

		break
	case err := <-watcher.Errors:
		log.Errorf("Error in fsnotify: %v", err)
		return
	}
}

func consumeEvent(ok bool, ctx *watchContext) bool {
	if !ok {
		return false
	}

	if ctx.filename != "" && filepath.Base(ctx.event.Name) != ctx.filename {
		log.Tracef("fsnotify irreleventa event different file %+v", ctx.event)
		return true
	}

	consumeRelevantEvents(ctx)

	return true
}

func consumeRelevantEvents(ctx *watchContext) {
	if ctx.event.Has(ctx.interestedEvent) {
		log.Debugf("fsnotify event relevant: %v", ctx.event)

		processDebounce(ctx)
	} else {
		log.Debugf("fsnotify event irrelevant: %v", ctx.event)
	}
}

func processDebounce(ctx *watchContext) {
	debounceWriteLogMutex.Lock()

	logEntry, found := debounceWriteLog[ctx.filename]

	if !found {
		logEntry = &FsNotifyLogEntry{
			callbackComplete: false,
			callbackWrapper:  nil,
		}

		debounceWriteLog[ctx.filename] = logEntry
	}

	log.Debugf("fsnotify event %+v", logEntry)

	if logEntry.callbackComplete || logEntry.callbackWrapper == nil {
		log.Debugf("fsnotify event callback queued within debounce delay: %v", ctx.filename)

		logEntry.callbackComplete = false
		logEntry.callbackWrapper = time.AfterFunc(debounceDelay, func() {
			log.Debugf("fsnotify event callback being fired: %v", ctx.filename)

			ctx.callback(ctx.event.Name)

			logEntry.callbackComplete = true
		})
	} else {
		log.Debugf("fsnotify event suppressed because it's within the debounce delay: %v", ctx.filename)
	}

	debounceWriteLogMutex.Unlock()
}