"""Database engine, session factory, and declarative base.

All services use the async SQLAlchemy API via ``get_session()``.
Alembic migrations use the synchronous psycopg2 URL (see alembic/env.py).
"""

from __future__ import annotations

from collections.abc import AsyncGenerator

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

from shared.config import settings

engine = create_async_engine(
    settings.DATABASE_URL,
    pool_pre_ping=True,
    echo=False,
)

async_session = async_sessionmaker(engine, expire_on_commit=False)


class Base(DeclarativeBase):
    """Shared declarative base for all ORM models."""


async def get_session() -> AsyncGenerator[AsyncSession, None]:
    """FastAPI dependency that yields an async DB session per request."""
    async with async_session() as session:
        yield session