import os
from typing import AsyncGenerator

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

DATABASE_URL = os.getenv("DATABASE_URL", "").strip()
if not DATABASE_URL:
    raise RuntimeError("DATABASE_URL is required (e.g. postgresql+asyncpg://...)")

engine = create_async_engine(DATABASE_URL, pool_pre_ping=True)

SessionLocal = async_sessionmaker(
    bind=engine,
    class_=AsyncSession,
    autoflush=False,
    expire_on_commit=False,
)

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