"""Async engine, session factory and the per-request session dependency."""

import os
from collections.abc import AsyncIterator
from typing import Annotated

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

DATABASE_URL = os.environ.get("DATABASE_URL", "sqlite+aiosqlite:///./app.db")

engine = create_async_engine(DATABASE_URL, pool_pre_ping=True)
# expire_on_commit=False: attributes stay loaded after commit, so building the
# response does not trigger a lazy load (which raises under asyncio).
SessionFactory = async_sessionmaker(engine, expire_on_commit=False)


class Base(AsyncAttrs, DeclarativeBase):
    pass


async def get_session() -> AsyncIterator[AsyncSession]:
    async with SessionFactory() as session:
        yield session


SessionDep = Annotated[AsyncSession, Depends(get_session)]