diff --git a/2021/11/AccessibleDirectory.cs b/2021/11/AccessibleDirectory.cs
index a4af53d..ae18269 100644
--- a/2021/11/AccessibleDirectory.cs
+++ b/2021/11/AccessibleDirectory.cs
@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Text;
 
 namespace RyzStudio.IO
 {
@@ -214,16 +215,66 @@ namespace RyzStudio.IO
             string filename = Path.GetFileName(filepath);
             if (string.IsNullOrWhiteSpace(filename)) return null;
 
-            List<string> fileList = AccessibleDirectory.GetFiles(path, pattern, true);
-            if (fileList == null) return null;
-            if (fileList.Count <= 0) return null;
-            if (fileList.Count(x => (Path.GetFileName(x).Equals(filename))) < 0) return null;
+            bool returnNext = false;
+            foreach (string item in Directory.EnumerateFiles(path, "*", SearchOption.TopDirectoryOnly))
+            {
+                if (!MatchFileSearchPattern(pattern, Path.GetFileName(item)))
+                {
+                    continue;
+                }
 
-            int pos = fileList.FindIndex(x => Path.GetFileName(x).Equals(filename));
-            if (pos < 0) return null;
-            if (pos >= (fileList.Count - 1)) return null;
+                if (!IsFileAccessible(item))
+                {
+                    continue;
+                }
 
-            return fileList[(pos + 1)];
+                if (returnNext)
+                {
+                    return item;
+                }
+
+                if (Path.GetFileName(item).Equals(filename))
+                {
+                    returnNext = true;
+                }
+            }
+
+            return null;
+        }
+
+        public static string GetPreviousFile(string filepath, string pattern)
+        {
+            if (string.IsNullOrWhiteSpace(filepath)) return null;
+
+            string path = Path.GetDirectoryName(filepath);
+            if (string.IsNullOrWhiteSpace(path)) return null;
+
+            string filename = Path.GetFileName(filepath);
+            if (string.IsNullOrWhiteSpace(filename)) return null;
+
+            StringBuilder sb = new StringBuilder();
+            foreach (string item in Directory.EnumerateFiles(path, "*", SearchOption.TopDirectoryOnly))
+            {
+                if (!MatchFileSearchPattern(pattern, Path.GetFileName(item)))
+                {
+                    continue;
+                }
+
+                if (!IsFileAccessible(item))
+                {
+                    continue;
+                }
+
+                sb.Clear();
+                sb.Append(item);
+
+                if (Path.GetFileName(item).Equals(filename))
+                {
+                    return (sb.Length <= 0) ? null : sb.ToString();
+                }
+            }
+
+            return null;
         }
 
         public static bool IsAccessible(string path)