from sqlmodel import Field, SQLModel, create_engine
from sqlalchemy.ext.asyncio.engine import create_async_engine
from sqlalchemy.orm.session import sessionmaker
from sqlalchemy.ext.asyncio.session import AsyncSession


class DB:
    # instance = None
    config = None
    engine = None
    async_engine = None
    session_maker = None

    def __new__(cls):
        if not hasattr(cls, 'instance'):
            cls.instance = super(DB, cls).__new__(cls)
        return cls.instance

    def __init__(self):
        from db import config
        self.config = config
        sqlite_url = self.config['DATABASE_URI']

        self.engine = create_engine(sqlite_url, echo=True)

        SQLModel.metadata.create_all(self.engine)

    def get_engine(self):
        return self.engine

    def create_async_engine(self):
        self.async_engine = create_async_engine(self.config['DATABASE_URI'], furure=True)
        self.session_maker = sessionmaker(self.async_engine, expire_on_commit=False, class_=AsyncSession)


class DBException(Exception):
    def __init__(self, *args):
        self.is_db = True
        if args:
            self.msg = args[0]
        else:
            self.msg = None

    def __str__(self):
        if self.msg:
            return "DB error, {0}".format(self.msg)
        else:
            return "DB error"