"""
control/base.py
---------------
Standalone SQLAlchemy foundation for the control plane.

`ControlBase` keeps control-plane table metadata fully separate from the
tenant-schema models declared on `app.db.Model`. The engine is built lazily
from the `CONTROL_DATABASE_URL` environment variable.
"""

import os
from contextlib import contextmanager

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

# Every control model subclasses this base — its own metadata collection.
ControlBase = declarative_base()


def get_control_database_url() -> str:
    """Return CONTROL_DATABASE_URL or raise a clear error if unset."""
    url = os.environ.get('CONTROL_DATABASE_URL')
    if not url:
        raise RuntimeError(
            "CONTROL_DATABASE_URL is not set. Example: "
            "mysql+pymysql://jqc_control:password@localhost/jqc_control"
        )
    return url


_engine = None
_Session = None


def get_engine():
    """Lazily build (and cache) the control-plane engine."""
    global _engine
    if _engine is None:
        _engine = create_engine(
            get_control_database_url(),
            pool_pre_ping=True,
            pool_recycle=1800,
            future=True,
        )
    return _engine


def get_sessionmaker():
    """Lazily build (and cache) the control-plane sessionmaker."""
    global _Session
    if _Session is None:
        _Session = sessionmaker(
            bind=get_engine(), future=True, expire_on_commit=False
        )
    return _Session


@contextmanager
def control_session():
    """Context-managed session — commits on success, rolls back on error.

    Usage:
        with control_session() as s:
            s.add(obj)
    """
    session = get_sessionmaker()()
    try:
        yield session
        session.commit()
    except Exception:
        session.rollback()
        raise
    finally:
        session.close()