Added thumbnails

Merge remote-tracking branch 'cover/thumbnails' into development

# Conflicts:
#	cps/admin.py
#	cps/templates/layout.html
#	cps/ub.py
#	cps/web.py
Update join for sqlalchemy 1.4

cps/ub.py

@@ -18,6 +18,7 @@
 #  along with this program. If not, see <http://www.gnu.org/licenses/>.
 
 from __future__ import division, print_function, unicode_literals
+import atexit
 import os
 import sys
 import datetime
@@ -441,6 +442,27 @@ class RemoteAuthToken(Base):
         return '<Token %r>' % self.id
 
 
+def filename(context):
+    file_format = context.get_current_parameters()['format']
+    if file_format == 'jpeg':
+        return context.get_current_parameters()['uuid'] + '.jpg'
+    else:
+        return context.get_current_parameters()['uuid'] + '.' + file_format
+
+
+class Thumbnail(Base):
+    __tablename__ = 'thumbnail'
+
+    id = Column(Integer, primary_key=True)
+    book_id = Column(Integer)
+    uuid = Column(String, default=lambda: str(uuid.uuid4()), unique=True)
+    format = Column(String, default='jpeg')
+    resolution = Column(SmallInteger, default=1)
+    filename = Column(String, default=filename)
+    generated_at = Column(DateTime, default=lambda: datetime.datetime.utcnow())
+    expiration = Column(DateTime, default=lambda: datetime.datetime.utcnow() + datetime.timedelta(days=30))
+
+
 # Add missing tables during migration of database
 def add_missing_tables(engine, session):
     if not engine.dialect.has_table(engine.connect(), "book_read_link"):
@@ -455,6 +477,8 @@ def add_missing_tables(engine, session):
         KoboStatistics.__table__.create(bind=engine)
     if not engine.dialect.has_table(engine.connect(), "archived_book"):
         ArchivedBook.__table__.create(bind=engine)
+    if not engine.dialect.has_table(engine.connect(), "thumbnail"):
+        Thumbnail.__table__.create(bind=engine)
     if not engine.dialect.has_table(engine.connect(), "registration"):
         Registration.__table__.create(bind=engine)
         with engine.connect() as conn:
@@ -725,6 +749,16 @@ def init_db(app_db_path):
             sys.exit(3)
 
 
+def get_new_session_instance():
+    new_engine = create_engine(u'sqlite:///{0}'.format(cli.settingspath), echo=False)
+    new_session = scoped_session(sessionmaker())
+    new_session.configure(bind=new_engine)
+
+    atexit.register(lambda: new_session.remove() if new_session else True)
+
+    return new_session
+
+
 def dispose():
     global session