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# Copyright 2010 United States Government as represented by the
# Administrator of the National Aeronautics and Space Administration.
# All Rights Reserved.
#
#    Licensed under the Apache License, Version 2.0 (the "License"); you may
#    not use this file except in compliance with the License. You may obtain
#    a copy of the License at
#
#         http://www.apache.org/licenses/LICENSE-2.0
#
#    Unless required by applicable law or agreed to in writing, software
#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
#    License for the specific language governing permissions and limitations
#    under the License.

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

import re
import time

from oslo.config import cfg
import sqlalchemy
import sqlalchemy.exc as exc
import sqlalchemy.orm
import sqlalchemy.pool as pool

from ceilometer.openstack.common import log


LOG = log.getLogger(__name__)

_MAKER = None
_ENGINE = None

sql_opts = [
    cfg.IntOpt('sql_connection_debug',
               default=0,
               help='Verbosity of SQL debugging information. 0=None, '
                    '100=Everything'),
    cfg.BoolOpt('sql_connection_trace',
                default=False,
                help='Add python stack traces to SQL as comment strings'),
    cfg.BoolOpt('sqlite_synchronous',
                default=True,
                help='If passed, use synchronous mode for sqlite'),
    cfg.IntOpt('sql_idle_timeout',
               default=3600,
               help='timeout before idle sql connections are reaped'),
    cfg.IntOpt('sql_max_retries',
               default=10,
               help='maximum db connection retries during startup. '
                    '(setting -1 implies an infinite retry count)'),
    cfg.IntOpt('sql_retry_interval',
               default=10,
               help='interval between retries of opening a sql connection'),
]

cfg.CONF.register_opts(sql_opts)


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

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

    session = _MAKER()
    return session


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


def add_regexp_listener(dbapi_con, con_record):
    """Add REGEXP function to sqlite connections."""

    def regexp(expr, item):
        reg = re.compile(expr)
        return reg.search(unicode(item)) is not None
    dbapi_con.create_function('regexp', 2, regexp)


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, ex:
        if ex.args[0] in (2006, 2013, 2014, 2045, 2055):
            LOG.warn('Got mysql server has gone away: %s', ex)
            raise exc.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(
            cfg.CONF.database_connection)

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

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

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

            if cfg.CONF.database_connection == "sqlite://":
                engine_args["poolclass"] = pool.StaticPool
                engine_args["connect_args"] = {'check_same_thread': False}

        _ENGINE = sqlalchemy.create_engine(cfg.CONF.database_connection,
                                           **engine_args)

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

        if (cfg.CONF.sql_connection_trace and
                _ENGINE.dialect.dbapi.__name__ == 'MySQLdb'):
            import MySQLdb.cursors
            _do_query = debug_mysql_do_query()
            setattr(MySQLdb.cursors.BaseCursor, '_do_query', _do_query)

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

            remaining = cfg.CONF.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(cfg.CONF.sql_retry_interval)
                try:
                    _ENGINE.connect()
                    break
                except exc.OperationalError, 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, autoflush=True):
    """Return a SQLAlchemy sessionmaker using the given engine."""
    return sqlalchemy.orm.sessionmaker(bind=engine,
                                       autocommit=autocommit,
                                       autoflush=autoflush,
                                       expire_on_commit=expire_on_commit)