"""Database engine, sessions and schema lifecycle helpers."""

from __future__ import annotations

from collections.abc import Iterator
from contextlib import contextmanager

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

from cayceops.models import Base

_engine = None
_factory: sessionmaker | None = None


def engine(url: str | None = None):
    """Return (and cache) the process SQLAlchemy engine."""
    global _engine
    if _engine is None:
        from cayceops.config import load

        _engine = create_engine(url or load().database_url, future=True)
    return _engine


def reset_engine() -> None:
    """Drop the cached engine (used by tests and CLI re-entry)."""
    global _engine, _factory
    if _engine is not None:
        _engine.dispose()
    _engine = None
    _factory = None


def session_factory():
    global _factory
    if _factory is None:
        _factory = sessionmaker(bind=engine(), expire_on_commit=False, future=True)
    return _factory


@contextmanager
def session_scope() -> Iterator[Session]:
    """Transactional scope: commit on success, rollback on error."""
    s = session_factory()()
    try:
        yield s
        s.commit()
    except Exception:
        s.rollback()
        raise
    finally:
        s.close()


def init_db() -> None:
    """Create all tables from metadata (dev/test convenience).

    Production uses Alembic migrations (``cayceops db upgrade``).
    """
    Base.metadata.create_all(engine())


def upgrade_db() -> None:
    """Run Alembic migrations to head."""
    from alembic.config import Config as AlembicConfig

    from alembic import command
    from cayceops.config import load

    cfg = AlembicConfig("alembic.ini")
    cfg.set_main_option("script_location", "alembic")
    cfg.set_main_option("sqlalchemy.url", load().database_url)
    command.upgrade(cfg, "head")


def current_revision() -> str | None:
    with engine().connect() as conn:
        row = conn.execute(text("SELECT version_num FROM alembic_version")).first()
        return row[0] if row else None