start building a directory hierarchy instead of a flat result

src/Tahoe/MagicFoldr.hs

@@ -82,7 +82,7 @@ type Grid = Map.Map StorageServerID StorageServerAnnouncement
 
 data FolderEntry
     = Directory
-        { directoryChildren :: Map.Map DecodedPath FolderEntry
+        { directoryChildren :: Map.Map T.Text FolderEntry
         }
     | File
         { fileContent :: CHK.Reader
@@ -138,7 +138,11 @@ getFolderFiles grid MagicFolder{folderCollectiveReadCap, ourPersonalWriteCap} =
             -- XXX Lose the parse errors here.  They don't fit into a simple
             -- Directory representation.  Do something about this so errors
             -- are visible.
-            pure . Right . Directory $ Map.fromList parsedEntries
+            pure . Right . foldr addToHierarchy Directory{directoryChildren = mempty} $ parsedEntries
+
+addToHierarchy :: (DecodedPath, FolderEntry) -> FolderEntry -> FolderEntry
+addToHierarchy (DecodedPath [basename], entry) d@Directory{directoryChildren} =
+    d{directoryChildren = Map.insert basename entry directoryChildren}
 
 snapshotToEntry :: Snapshot -> Maybe FolderEntry
 snapshotToEntry Snapshot{snapshotContentCap, snapshotMetadataCap} = Just $ File snapshotContentCap snapshotMetadataCap