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

import settings


engine = create_engine(settings.connection_uri)
BaseSession = sessionmaker(bind=engine)


class Singleton(type):

    def __init__(cls, *args, **kwargs):
        super(Singleton, cls).__init__(*args, **kwargs)
        cls.instance = None

    def __call__(cls, *args, **kwargs):
        if cls.instance is None:
            cls.instance = super(Singleton, cls).__call__(*args, **kwargs)
        return cls.instance


class Session(BaseSession):

    __metaclass__ = Singleton


class Base(object):

    @declared_attr
    def __tablename__(cls):
        return cls.__name__

    session = Session()
    id = Column(Integer, primary_key=True)

    def save(self):
        self.session.add(self)
        self.session.commit()


Base = declarative_base(cls=Base)


class TestTable(Base):

    pass