from contextlib import contextmanager

from sqlalchemy import Column, Integer, String, create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker


engine = create_engine('sqlite:///db.db', convert_unicode=True)
session_factory = sessionmaker(autocommit=False,
                               autoflush=False,
                               bind=engine)


@contextmanager
def Session():
    session = session_factory()
    try:
        yield session
        session.commit()
    except:
        session.rollback()
        raise
    finally:
        session.close()


Base = declarative_base()


class User(Base):
    __tablename__ = 'users'

    id = Column(Integer, primary_key=True)
    username = Column(String, nullable=False, unique=True)
    passwordhash = Column(String, nullable=False)


def init_db():
    Base.metadata.create_all(bind=engine)