Add singleton playlist manager

Currently implemented is queing, dequening, and automatic title fetch
using metadatafetch.

grzegorz/__init__.py

@@ -1,7 +1,9 @@
 import asyncio
+from . import playlistmanage
 
 async def entry():
     await asyncio.wait([
+        playlistmanage.metadatafetch_loop(),
     ])
 
 def main():

grzegorz/playlistmanage.py

@@ -0,0 +1,34 @@
+import asyncio
+
+from . import metadatafetch
+from . import nyasync
+
+metadatafetch_queue = nyasync.Queue()
+async def metadatafetch_loop():
+    async for item in metadatafetch_queue:
+        title = await metadatafetch.title(item.url)
+        item.title = title
+        metadatafetch_queue.task_done()
+
+class PlaylistItem:
+    def __init__(self, url):
+        self.url = url
+        self.title = None
+
+class Playlist:
+    def __init__(self):
+        self.playlist = []
+        self.nonempty = nyasync.Condition(lambda: self.playlist)
+        self.change = nyasync.Event()
+
+    def queue(self, url):
+        item = PlaylistItem(url)
+        self.playlist.append(item)
+        metadatafetch_queue.put_nowait(item)
+        self.nonempty.notify()
+        self.change.notify()
+
+    async def dequeue(self) -> PlaylistItem:
+        await self.nonempty
+        self.change.notify()
+        return self.playlist.pop(0)