/// <summary>
        /// Removing oldest cache file (file, which last access time is smaller)
        /// </summary>
        private bool RemoveOldestCacheFile()
        {
            if (_lastAccessTimeDictionary.Count == 0)
            {
                return(false);
            }

            var oldestCacheFilePath = _lastAccessTimeDictionary.Aggregate((pair1, pair2) => (pair1.Value < pair2.Value)? pair1 : pair2).Key;

            if (String.IsNullOrEmpty(oldestCacheFilePath))
            {
                return(false);
            }

            try
            {
                long fileSizeInBytes;

                using (var file = ISF.OpenFile(oldestCacheFilePath, FileMode.Open, FileAccess.Read))
                {
                    fileSizeInBytes = file.Length;
                }

                try
                {
                    ISF.DeleteFile(oldestCacheFilePath);
                    _lastAccessTimeDictionary.Remove(oldestCacheFilePath);
                    CurrentCacheSizeInBytes -= fileSizeInBytes; // Updating current cache size

                    JetImageLoader.Log("[delete] cache file " + oldestCacheFilePath);
                    return(true);
                }
                catch
                {
                    JetImageLoader.Log("[error] can not delete oldest cache file: " + oldestCacheFilePath);
                }
            }
            catch
            {
                JetImageLoader.Log("[error] can not get olders cache's file size: " + oldestCacheFilePath);
            }

            return(false);
        }
        private void BeginCountCurrentCacheSize()
        {
            Task.Factory.StartNew(() =>
            {
                // Pattern to match all innerFiles and innerDirectories inside absoluteDirPath
                var filesAndDirectoriesPattern = CacheDirectory + @"\*";

                string[] cacheFileNames;

                try
                {
                    cacheFileNames = ISF.GetFileNames(Path.Combine(CacheDirectory, filesAndDirectoriesPattern));
                }
                catch
                {
                    return;
                }

                long cacheSizeInBytes = 0;

                foreach (var cacheFileName in cacheFileNames)
                {
                    var fullCacheFilePath = Path.Combine(CacheDirectory, cacheFileName);

                    try
                    {
                        using (var file = ISF.OpenFile(fullCacheFilePath, FileMode.Open, FileAccess.Read))
                        {
                            cacheSizeInBytes += file.Length;

                            _lastAccessTimeDictionary.Add(fullCacheFilePath, DateTimeUtil.ConvertDateTimeToMillis(ISF.GetLastAccessTime(fullCacheFilePath).DateTime));
                        }
                    }
                    catch
                    {
                        JetImageLoader.Log("[error] can not get cache's file size: " + fullCacheFilePath);
                    }
                }

                CurrentCacheSizeInBytes += cacheSizeInBytes; // Updating current cache size
            });
        }