"""Database access for the FastAPI web app."""

from __future__ import annotations

from collections.abc import Iterator
from contextlib import contextmanager
from functools import lru_cache

from sqlalchemy.engine import Engine
from sqlalchemy.orm import Session

from pipelines.orm.common import get_postgres_engine


@lru_cache(maxsize=1)
def get_engine() -> Engine:
    """Return the lazily-created DATA_SCIENCE_DEV SQLAlchemy engine."""
    return get_postgres_engine(name="DATA_SCIENCE_DEV")


def validate_database_connection() -> None:
    """Fail fast if the configured DATA_SCIENCE_DEV database is unavailable."""
    with get_engine().connect():
        pass


@contextmanager
def session_scope() -> Iterator[Session]:
    """Yield a SQLAlchemy session for a read-only request."""
    with Session(get_engine()) as session:
        yield session