from typing import AsyncIterator

from fastapi import Request
from sqlalchemy.ext.asyncio import (
    AsyncEngine,
    AsyncSession,
    async_sessionmaker,
    create_async_engine,
)


def create_engine(database_url: str) -> AsyncEngine:
    return create_async_engine(database_url)


def create_session_factory(engine: AsyncEngine) -> async_sessionmaker[AsyncSession]:
    # expire_on_commit=False keeps ids/attributes readable after commit
    return async_sessionmaker(engine, expire_on_commit=False)


async def get_session(request: Request) -> AsyncIterator[AsyncSession]:
    """FastAPI dependency: one session per request, factory is set in the app lifespan."""
    async with request.app.state.session_factory() as session:
        yield session