files tree made better.

src/Yavsc.Abstract/FileSystem/FileSystemHelpers.cs

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+using System.IO;
+using System.Linq;
+using System.Security.Claims;
+using System.Text;
+using Yavsc.ViewModels.UserFiles;
+
+namespace Yavsc.Abstract.FileSystem
+{
+    public static class AbstractFileSystemHelpers
+    {
+
+        public static string UserBillsDirName {  set; get; }
+        public static string UserFilesDirName {  set; get; }
+        
+        public static bool IsValidYavscPath(this string path)
+        {
+            if (string.IsNullOrEmpty(path)) return true;
+            foreach (var name in path.Split(Path.DirectorySeparatorChar))
+            {
+                if (!IsValidDirectoryName(name) || name.Equals("..") || name.Equals("."))
+                        return false;
+            }
+            if (path[path.Length-1]==FileSystemConstants.RemoteDirectorySeparator) return false;
+            return true;
+        }
+        public static bool IsValidDirectoryName(this string name)
+        {
+            return !name.Any(c => !FileSystemConstants.ValidFileNameChars.Contains(c));
+        }
+        // Ensure this path is canonical,
+        // No "dirto/./this", neither "dirt/to/that/"
+        // no .. and each char must be listed as valid in constants
+
+        public static string FilterFileName(string fileName)
+        {
+            if (fileName==null) return null;
+            StringBuilder sb = new StringBuilder();
+            foreach (var c in fileName)
+            {
+                if (FileSystemConstants.ValidFileNameChars.Contains(c))
+                    sb.Append(c);
+                else sb.Append('_');
+            }
+           return sb.ToString();
+        }
+  
+        public static UserDirectoryInfo GetUserFiles(this ClaimsPrincipal user, string subdir)
+        {
+
+            UserDirectoryInfo di = new UserDirectoryInfo(UserFilesDirName, user.Identity.Name, subdir);
+
+            return di;
+        }
+        
+        
+    }
+
+    public static  class FileSystemConstants
+    {
+        public const char RemoteDirectorySeparator = '/';
+        public static char[] ValidFileNameChars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-=_~. ".ToCharArray();
+    }
+}