Allow sonos to select playlists as a source (#8258)

* Allow sonos to select playlists as a source

Most of this was taken from
https://github.com/home-assistant/home-assistant/issues/5598#issuecomment-278229895
however I made a few small improvements so that it works for other
services than Spotify and it should properly switch to playing the queue
if you had another song playing previously.

/cc @PatBoud

* Attempt to fix style issues

* More indent changes

* Fix misplaced period

* Move playlist replacement to function

* Privatize replace_queue_with_playlist and explain

* Remove unneeded decorator

* Fix doc formatting

homeassistant/components/media_player/sonos.py

@@ -893,7 +893,44 @@ class SonosDevice(MediaPlayerDevice):
             if len(fav) == 1:
                 src = fav.pop()
                 self._source_name = src['title']
-                self._player.play_uri(src['uri'], src['meta'], src['title'])
+
+                if 'object.container.playlistContainer' in src['meta']:
+                    self._replace_queue_with_playlist(src)
+                    self._player.play_from_queue(0)
+                else:
+                    self._player.play_uri(src['uri'], src['meta'],
+                                          src['title'])
+
+    def _replace_queue_with_playlist(self, src):
+        """Replace queue with playlist represented by src.
+
+        Playlists can't be played directly with the self._player.play_uri
+        API as they are actually composed of mulitple URLs. Until soco has
+        suppport for playing a playlist, we'll need to parse the playlist item
+        and replace the current queue in order to play it.
+        """
+        import soco
+        import xml.etree.ElementTree as ET
+
+        root = ET.fromstring(src['meta'])
+        namespaces = {'item':
+                      'urn:schemas-upnp-org:metadata-1-0/DIDL-Lite/',
+                      'desc': 'urn:schemas-upnp-org:metadata-1-0/DIDL-Lite/'}
+        desc = root.find('item:item', namespaces).find('desc:desc',
+                                                       namespaces).text
+
+        res = [soco.data_structures.DidlResource(uri=src['uri'],
+                                                 protocol_info="DUMMY")]
+        didl = soco.data_structures.DidlItem(title="DUMMY",
+                                             parent_id="DUMMY",
+                                             item_id=src['uri'],
+                                             desc=desc,
+                                             resources=res)
+
+        self._player.stop()
+        self._player.clear_queue()
+        self._player.play_mode = 'NORMAL'
+        self._player.add_to_queue(didl)
 
     @property
     def source_list(self):