# vim: tabstop=4 shiftwidth=4 softtabstop=4

# Copyright (c) 2013 TrilioData, Inc.
# All Rights Reserved.

"""Session Handling for SQLAlchemy backend."""

import time

from sqlalchemy.exc import DisconnectionError, OperationalError
import sqlalchemy.orm
from sqlalchemy.pool import NullPool, StaticPool

import workloadmgr.exception
import workloadmgr.flags as flags
from workloadmgr.openstack.common import log as logging


FLAGS = flags.FLAGS
LOG = logging.getLogger(__name__)

_ENGINE = None
_MAKER = None


def get_session(autocommit=True, expire_on_commit=False):
    """Return a SQLAlchemy session."""
    global _MAKER

    if _MAKER is None:
        engine = get_engine()
        _MAKER = get_maker(engine, autocommit, expire_on_commit)

    session = _MAKER()
    session.query = workloadmgr.exception.wrap_db_error(session.query)
    session.flush = workloadmgr.exception.wrap_db_error(session.flush)
    return session


def synchronous_switch_listener(dbapi_conn, connection_rec):
    """Switch sqlite connections to non-synchronous mode"""
    dbapi_conn.execute("PRAGMA synchronous = OFF")


def ping_listener(dbapi_conn, connection_rec, connection_proxy):
    """
    Ensures that MySQL connections checked out of the
    pool are alive.

    Borrowed from:
    http://groups.google.com/group/sqlalchemy/msg/a4ce563d802c929f
    """
    try:
        dbapi_conn.cursor().execute('select 1')
    except dbapi_conn.OperationalError as ex:
        if ex.args[0] in (2006, 2013, 2014, 2045, 2055):
            LOG.warn(_('Got mysql server has gone away: %s'), ex)
            raise DisconnectionError("Database server went away")
        else:
            raise


def is_db_connection_error(args):
    """Return True if error in connecting to db."""
    # NOTE(adam_g): This is currently MySQL specific and needs to be extended
    #               to support Postgres and others.
    conn_err_codes = ('2002', '2003', '2006')
    for err_code in conn_err_codes:
        if args.find(err_code) != -1:
            return True
    return False


def get_engine():
    """Return a SQLAlchemy engine."""
    global _ENGINE
    if _ENGINE is None:
        connection_dict = sqlalchemy.engine.url.make_url(FLAGS.sql_connection)

        engine_args = {
            "pool_recycle": FLAGS.sql_idle_timeout,
            "echo": False,
            'convert_unicode': True,
        }

        # Map our SQL debug level to SQLAlchemy's options
        if FLAGS.sql_connection_debug >= 100:
            engine_args['echo'] = 'debug'
        elif FLAGS.sql_connection_debug >= 50:
            engine_args['echo'] = True

        if "sqlite" in connection_dict.drivername:
            engine_args["poolclass"] = NullPool

            if FLAGS.sql_connection == "sqlite://":
                engine_args["poolclass"] = StaticPool
                engine_args["connect_args"] = {'check_same_thread': False}

        engine_args['pool_pre_ping'] = True
        _ENGINE = sqlalchemy.create_engine(FLAGS.sql_connection, **engine_args)

        if 'mysql' in connection_dict.drivername:
            sqlalchemy.event.listen(_ENGINE, 'checkout', ping_listener)
        elif "sqlite" in connection_dict.drivername:
            if not FLAGS.sqlite_synchronous:
                sqlalchemy.event.listen(_ENGINE, 'connect',
                                        synchronous_switch_listener)

        try:
            _ENGINE.connect()
        except OperationalError as e:
            if not is_db_connection_error(e.args[0]):
                raise

            remaining = FLAGS.sql_max_retries
            if remaining == -1:
                remaining = 'infinite'
            while True:
                msg = _('SQL connection failed. %s attempts left.')
                LOG.warn(msg % remaining)
                if remaining != 'infinite':
                    remaining -= 1
                time.sleep(FLAGS.sql_retry_interval)
                try:
                    _ENGINE.connect()
                    break
                except OperationalError as e:
                    if ((remaining != 'infinite' and remaining == 0) or
                            not is_db_connection_error(e.args[0])):
                        raise
    return _ENGINE


def get_maker(engine, autocommit=True, expire_on_commit=False):
    """Return a SQLAlchemy sessionmaker using the given engine."""
    return sqlalchemy.orm.sessionmaker(bind=engine,
                                       autocommit=autocommit,
                                       expire_on_commit=expire_on_commit)