from typing import AsyncGenerator

from sqlalchemy.ext.asyncio import AsyncSession, async_sessionmaker, create_async_engine
from sqlalchemy.orm import DeclarativeBase

from app.config import settings


class Base(DeclarativeBase):
    pass


def _make_engine():
    return create_async_engine(settings.database_url, echo=False)


def _make_session_factory(engine):
    return async_sessionmaker(engine, expire_on_commit=False)


# Lazily initialised on first use so tests can patch settings before import
_engine = None
_session_factory = None


def get_engine():
    global _engine
    if _engine is None:
        _engine = _make_engine()
    return _engine


def get_session_factory():
    global _session_factory
    if _session_factory is None:
        _session_factory = _make_session_factory(get_engine())
    return _session_factory


# Alias kept for Alembic and bot usage
AsyncSessionLocal = None  # populated on first call to get_session_factory()


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    factory = get_session_factory()
    async with factory() as session:
        yield session