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

from config import settings

engine = create_async_engine(
    settings.database_url,
    echo=False,         # logs all SQL — set False in production
    pool_size=10,
    max_overflow=20,
    pool_pre_ping=True,   # reconnect if Neon pooler closed an idle connection
    pool_recycle=300,
)

AsyncSessionLocal = async_sessionmaker(
    bind=engine,
    class_=AsyncSession,
    expire_on_commit=False,
)


class Base(DeclarativeBase):
    pass


async def get_db() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency — yields a session and closes it after the request."""
    async with AsyncSessionLocal() as session:
        try:
            yield session
            await session.commit()
        except Exception:
            await session.rollback()
            raise
        finally:
            await session.close()