Enable play_folder to play single songs as well

Having one common way to play single songs as well as folders, harmonizes
how metadata is stored by the player. This makes it easier to
implement functionality working with both.

src/jukebox/jukebox/playlistgenerator.py

@@ -70,6 +70,14 @@
 TYPE_DECODE = ['file', 'directory', 'stream', 'podcast']
 
 
+class PseudoDirEntry:
+   def __init__(self, path):
+      import os, os.path
+      self.path = os.path.realpath(path)
+      self.name = os.path.basename(self.path)
+      self.is_dir = os.path.isdir(self.path)
+      self.stat = lambda: os.stat(self.path)
+
 class PlaylistEntry:
     def __init__(self, filetype: int, name: str, path: str):
         self._type = filetype
@@ -230,11 +238,15 @@ def _get_directory_content(self, path='.') -> List[PlaylistEntry]:
         files = []
         playlist = []
         self._folder = os.path.abspath(os.path.join(self._music_library_base_path, path))
-        for f in os.scandir(self._folder):
-            if f.is_dir(follow_symlinks=True):
-                dirs.append(f)
-            if self._is_valid(f):
-                files.append(f)
+        if os.path.isfile(self._folder):
+            files.append(PseudoDirEntry(self._folder))
+            path = os.path.dirname(self._folder)
+        else:
+            for f in os.scandir(self._folder):
+                if f.is_dir(follow_symlinks=True):
+                    dirs.append(f)
+                if self._is_valid(f):
+                    files.append(f)
         # Sort the directory content (case in-sensitive) to give reproducible results across different machines
         # And do this before parsing special content files. Reason: If there is a special content file (e.g. podcast)
         # which links to multiple streams, these will already be ordered