from contextlib import contextmanager
from typing import Iterator, Optional

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

import settings

_ENGINE = None
_SESSION_FACTORY: Optional[sessionmaker] = None


def _get_database_url() -> str:
    return settings.get_database_url()


def get_engine():
    global _ENGINE
    if _ENGINE is None:
        _ENGINE = create_engine(
            _get_database_url(),
            pool_pre_ping=True,
            pool_size=int(os.getenv("DB_POOL_SIZE", "10")),
            max_overflow=int(os.getenv("DB_POOL_MAX_OVERFLOW", "20")),
            pool_timeout=int(os.getenv("DB_POOL_TIMEOUT", "30")),
        )
    return _ENGINE


def get_session_factory() -> sessionmaker:
    global _SESSION_FACTORY
    if _SESSION_FACTORY is None:
        _SESSION_FACTORY = sessionmaker(bind=get_engine(), autoflush=False, autocommit=False)
    return _SESSION_FACTORY


@contextmanager
def get_session() -> Iterator[Session]:
    session = get_session_factory()()
    try:
        yield session
        session.commit()
    except Exception:
        session.rollback()
        raise
    finally:
        session.close()