// InitPhysicalCache initializes the physical cache directories.
func InitPhysicalCache() {
	cachePath := config.BuildCachePath()
	if !utils.PathExists(cachePath) {
		err := os.Mkdir(cachePath, os.ModePerm)
		if err != nil {
		}
	}
 
	thumbnailsPath := config.BuildCachePath("thumbnails")
	if !utils.PathExists(thumbnailsPath) {
		err := os.Mkdir(thumbnailsPath, os.ModePerm)
		if err != nil {
		}
	}
}

// fetchFromDiskCache fetches the files from the disk cache and returns the list of files and the number of files.
func fetchFromDiskCache(dst string, uuid string) ([]string, int) {
	var files []string
	count := 0
 
	cacheWalk := func(s string, d fs.DirEntry, err error) error {
		if err != nil {
			log.Z.Error("failed to walk cache dir",
				zap.String("name", d.Name()),
				zap.String("err", err.Error()))
			return err
		}
		if d.IsDir() {
			return nil
		}
 
		// ReplaceAll ensures that the path is correct: cache/uuid/<arbitrary/path/image.png>
		files = append(files, strings.ReplaceAll(filepath.ToSlash(s), config.BuildCachePath(uuid)+"/", ""))
		count += 1
		return nil
	}
 
	err := filepath.WalkDir(dst, cacheWalk)
	if err != nil {
		log.Z.Error("failed to walk cache dir",
			zap.String("dst", dst),
			zap.String("err", err.Error()))
		return nil, 0
	}
 
	return files, count
}
 
// fetchOrExtractGallery extracts the gallery from the archive and returns the list of files and the number of files.
func fetchOrExtractGallery(archivePath string, uuid string) ([]string, int) {
	dst := config.BuildCachePath(uuid)
	if _, err := os.Stat(dst); errors.Is(err, fs.ErrNotExist) {
		return utils.UniversalExtract(dst, archivePath)
	}
 
	files, count := fetchFromDiskCache(dst, uuid)
	if count == 0 {
		err := os.Remove(dst)
		if err != nil {
			log.Z.Debug("removing empty cache dir failed",
				zap.String("dst", dst),
				zap.String("err", err.Error()))
			return nil, 0
		}
 
		return utils.UniversalExtract(dst, archivePath)
	}
	natsort.Sort(files)
 
	return files, count
}

type cacheValue struct {
	Accessed time.Time   // Used to determine when the cache entry was last accessed for expiring and pruning purposes.
	Mu       *sync.Mutex // Mutex to ensure file-write-safety when accessing the cache.
}
 
type GalleryCache struct {
	Path  string                // Path to the cache directory.
	Store map[string]cacheValue // Map of Mutexes and access times for each cache entry.
}
 
var galleryCache *GalleryCache

// InitGalleryCache initializes the abstraction layer for the gallery cache.
func InitGalleryCache() {
	galleryCache = &GalleryCache{
		Path:  config.BuildCachePath(),
		Store: make(map[string]cacheValue),
	}
 
	iterateCacheEntries(func(pathToEntry string, accessTime time.Time) {
		maybeUUID := path.Base(pathToEntry)
		if _, err := uuid.Parse(maybeUUID); err != nil {
			return
		}
 
		galleryCache.Store[path.Base(pathToEntry)] = cacheValue{
			Accessed: accessTime,
			Mu:       &sync.Mutex{},
		}
	})
}
 
// iterateCacheEntries iterates over all cache entries and calls the callback function for each entry.
func iterateCacheEntries(callback func(pathToEntry string, accessTime time.Time)) {
	cachePath := config.BuildCachePath()
	cacheEntries, err := os.ReadDir(cachePath)
	if err != nil {
		log.Z.Error("could not read cache dir",
			zap.String("path", cachePath),
			zap.String("err", err.Error()))
		return
	}
 
	for _, entry := range cacheEntries {
		info, err := entry.Info()
		if err != nil {
			log.Z.Error("could to read cache entry info",
				zap.String("path", cachePath),
				zap.String("err", err.Error()))
			return
		}
 
		pathToEntry := path.Join(cachePath, entry.Name())
		accessTime, err := atime.Stat(pathToEntry)
		if err != nil {
			log.Z.Debug("could to read the access time",
				zap.String("name", entry.Name()),
				zap.String("path", cachePath),
				zap.String("err", err.Error()))
			accessTime = info.ModTime()
		}
 
		callback(pathToEntry, accessTime)
	}
}

// Read reads the gallery while updating the mutex and access time.
func Read(archivePath string, galleryUUID string) ([]string, int) {
	if _, ok := galleryCache.Store[galleryUUID]; !ok {
		galleryCache.Store[galleryUUID] = cacheValue{
			Accessed: time.Now(),
			Mu:       &sync.Mutex{},
		}
	} else {
		galleryCache.Store[galleryUUID] = cacheValue{
			Accessed: time.Now(),
			Mu:       galleryCache.Store[galleryUUID].Mu,
		}
	}
 
	galleryCache.Store[galleryUUID].Mu.Lock()
	defer galleryCache.Store[galleryUUID].Mu.Unlock()
 
	files, count := fetchOrExtractGallery(archivePath, galleryUUID)
	if count == 0 {
		return files, count
	}
 
	return files, count
}

utils.PeriodicTask(time.Minute, cache.PruneCache)
 
// PeriodicTask loops the given function in separate thread between the given interval.
func PeriodicTask(d time.Duration, f func()) {
	go func() {
		for {
			f()
			time.Sleep(d)
		}
	}()
}

// PruneCache removes entries not accessed (internal timestamp in mem) in the last x time in a thread-safe manner.
func PruneCache() {
	now := time.Now()
	for galleryUUID, value := range galleryCache.Store {
		value.Mu.Lock()
		if value.Accessed.Add(config.Options.Cache.TTL).Before(now) {
			if err := remove(galleryUUID); err != nil {
				log.Z.Error("failed to delete a cache entry",
					zap.Bool("thread-safe", true),
					zap.String("uuid", galleryUUID),
					zap.String("err", err.Error()))
			}
		}
		value.Mu.Unlock()
	}
}
 
// remove wipes the cached gallery from the disk.
func remove(galleryUUID string) error {
	// Paranoid check to make sure that the base is a real UUID, since we don't want to delete anything else.
	maybeUUID := path.Base(galleryUUID)
	if _, err := uuid.Parse(maybeUUID); err != nil {
		delete(galleryCache.Store, galleryUUID)
		return err
	}
 
	galleryPath := config.BuildCachePath(galleryUUID)
	if err := os.RemoveAll(galleryPath); err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			delete(galleryCache.Store, galleryUUID)
		}
		return err
	}
 
	delete(galleryCache.Store, galleryUUID)
 
	return nil
}