"""SQLAlchemy util functions."""
from contextlib import contextmanager
import logging
import time

from sqlalchemy.exc import OperationalError, SQLAlchemyError

from .const import DATA_INSTANCE

_LOGGER = logging.getLogger(__name__)

RETRIES = 3
QUERY_RETRY_WAIT = 0.1


@contextmanager
def session_scope(*, hass=None, session=None):
    """Provide a transactional scope around a series of operations."""
    if session is None and hass is not None:
        session = hass.data[DATA_INSTANCE].get_session()

    if session is None:
        raise RuntimeError("Session required")

    need_rollback = False
    try:
        yield session
        if session.transaction:
            need_rollback = True
            session.commit()
    except Exception as err:
        _LOGGER.error("Error executing query: %s", err)
        if need_rollback:
            session.rollback()
        raise
    finally:
        session.close()


def commit(session, work):
    """Commit & retry work: Either a model or in a function."""
    for _ in range(0, RETRIES):
        try:
            if callable(work):
                work(session)
            else:
                session.add(work)
            session.commit()
            return True
        except OperationalError as err:
            _LOGGER.error("Error executing query: %s", err)
            session.rollback()
            time.sleep(QUERY_RETRY_WAIT)
    return False


def execute(qry, to_native=True):
    """Query the database and convert the objects to HA native form.

    This method also retries a few times in the case of stale connections.
    """
    for tryno in range(0, RETRIES):
        try:
            timer_start = time.perf_counter()
            if to_native:
                result = [
                    row for row in (row.to_native() for row in qry) if row is not None
                ]
            else:
                result = list(qry)

            if _LOGGER.isEnabledFor(logging.DEBUG):
                elapsed = time.perf_counter() - timer_start
                if to_native:
                    _LOGGER.debug(
                        "converting %d rows to native objects took %fs",
                        len(result),
                        elapsed,
                    )
                else:
                    _LOGGER.debug(
                        "querying %d rows took %fs", len(result), elapsed,
                    )

            return result
        except SQLAlchemyError as err:
            _LOGGER.error("Error executing query: %s", err)

            if tryno == RETRIES - 1:
                raise
            time.sleep(QUERY_RETRY_WAIT)