Add the token refresher.

Signed-off-by: Jan Losinski <losinski@wh2.tu-dresden.de>

refresher.py

@@ -0,0 +1,42 @@
+import asyncio
+from datetime import datetime, timedelta
+
+from logbook import Logger
+from sqlalchemy import func
+
+from models import User
+
+logger = Logger(__name__)
+
+
+class Refresher:
+    def __init__(self, session, wallabag):
+        self.session = session
+        self.wallabag = wallabag
+        self.grace = 120
+
+    def _wait_time(self):
+        next = self.session.query(func.min(User.token_valid).label("min")).first()
+        if next is None or next.min is None:
+            return 3
+        delta = next.min - datetime.utcnow()
+        if delta < timedelta(seconds=self.grace):
+            return 0
+
+        calculated = delta - timedelta(seconds=self.grace)
+        return calculated.total_seconds()
+
+    async def refresh(self):
+        while True:
+            await asyncio.sleep(self._wait_time())
+
+            ts = datetime.utcnow() + timedelta(seconds=self.grace)
+            refreshes = [self._refresh_user(user) for user
+                         in self.session.query(User).filter(User.token_valid < ts).all()]
+            await asyncio.gather(*refreshes)
+
+            self.session.commit()
+
+    async def _refresh_user(self, user):
+        logger.info("Refresh token for {}", user.name)
+        await self.wallabag.refresh_token(user)