"""Engine/session helpers. The DB URL comes from Env.database_url so the same
code runs on SQLite (default) or Postgres by changing one env var."""
from contextlib import contextmanager

from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker

from Env import database_url
from src.db.models import Base

_engine = create_engine(database_url, future=True)
SessionLocal = sessionmaker(bind=_engine, future=True, expire_on_commit=False)


def get_engine():
    return _engine


def init_db():
    """Create the storage dir + tables if missing (safe to call every run)."""
    from Env import data_dir

    data_dir.mkdir(parents=True, exist_ok=True)
    Base.metadata.create_all(_engine)


@contextmanager
def session_scope():
    """Transactional session: commit on success, roll back on error."""
    session = SessionLocal()
    try:
        yield session
        session.commit()
    except Exception:
        session.rollback()
        raise
    finally:
        session.close()