"""SQLAlchemy engine and session factory.

Note: Engine and session factory are cached globally per process. Only one
DATABASE_URL is effectively used for the process lifetime. Using a different
URL later (e.g. in tests with in-memory SQLite) would still use the first
engine. To support multiple URLs, cache by database_url (e.g. a dict keyed by URL).
"""

from contextlib import contextmanager
from typing import Generator

from sqlalchemy import create_engine
from sqlalchemy.orm import Session, sessionmaker


_engine = None
_SessionLocal = None


@contextmanager
def session_scope(database_url: str) -> Generator[Session, None, None]:
    """Context manager: yields a session and closes it on exit."""
    session = get_session(database_url)
    try:
        yield session
    finally:
        session.close()


def get_engine(database_url: str):
    global _engine
    if _engine is None:
        _engine = create_engine(
            database_url,
            connect_args={"check_same_thread": False}
            if "sqlite" in database_url
            else {},
            echo=False,
        )
    return _engine


def get_session_factory(database_url: str) -> sessionmaker[Session]:
    global _SessionLocal
    if _SessionLocal is None:
        engine = get_engine(database_url)
        _SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
    return _SessionLocal


def get_session(database_url: str) -> Session:
    return get_session_factory(database_url)()