# Copyright 2016 - Nokia Networks
#
#    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.

from __future__ import absolute_import

import functools

from sqlalchemy import exc as sqla_exc

from oslo_db import exception as db_exc
from oslo_log import log as logging

import tenacity

from mistral import context
from mistral import exceptions as exc
from mistral.services import security


LOG = logging.getLogger(__name__)

_RETRY_ERRORS = (
    db_exc.DBDeadlock,
    db_exc.DBConnectionError,
    sqla_exc.OperationalError
)


def _with_auth_context(auth_ctx, func, *args, **kw):
    """Runs the given function with the specified auth context.

    :param auth_ctx: Authentication context.
    :param func: Function to run with the specified auth context.
    :param args: Function positional arguments.
    :param kw: Function keyword arguments.
    :return: Function result.
    """
    old_auth_ctx = context.ctx() if context.has_ctx() else None

    context.set_ctx(auth_ctx)

    try:
        return func(*args, **kw)
    except Exception as e:
        # Note (rakhmerov): In case of "Too many connections" error from the
        # database it doesn't get wrapped with a SQLAlchemy exception for some
        # reason so we have to check the exception message explicitly.
        if isinstance(e, _RETRY_ERRORS) or 'Too many connections' in str(e):
            LOG.exception(
                "DB error detected, operation will be retried: %s", func
            )

        raise
    finally:
        context.set_ctx(old_auth_ctx)


def retry_on_db_error(func, retry=None):
    """Decorates the given function so that it retries on DB errors.

    Note that the decorator retries the function/method only on some
    of the DB errors that are considered to be worth retrying, like
    deadlocks and disconnections.

    :param func: Function to decorate.
    :param retry: a Retrying object
    :return: Decorated function.
    """
    if not retry:
        retry = tenacity.Retrying(
            retry=(
                tenacity.retry_if_exception_type(_RETRY_ERRORS) |
                tenacity.retry_if_exception_message(
                    match='Too many connections'
                )
            ),
            stop=tenacity.stop_after_attempt(50),
            wait=tenacity.wait_incrementing(start=0, increment=0.1, max=2)
        )

    # The `assigned` arg should be empty as some of the default values are not
    # supported by simply initialized MagicMocks. The consequence may
    # be that the representation will contain the wrapper and not the
    # wrapped function.
    @functools.wraps(func, assigned=[])
    def decorate(*args, **kw):
        # Retrying library decorator might potentially run a decorated
        # function within a new thread so it's safer not to apply the
        # decorator directly to a target method/function because we can
        # lose an authentication context.
        # The solution is to create one more function and explicitly set
        # auth context before calling it (potentially in a new thread).
        auth_ctx = context.ctx() if context.has_ctx() else None

        return retry.call(_with_auth_context, auth_ctx, func, *args, **kw)

    return decorate


def check_db_obj_access(db_obj):
    """Check accessibility to db object."""
    ctx = context.ctx()
    is_admin = ctx.is_admin

    if not is_admin and db_obj.project_id != security.get_project_id():
        raise exc.NotAllowedException(
            "Can not access %s resource of other projects, ID: %s" %
            (db_obj.__class__.__name__, db_obj.id)
        )

    if not is_admin and hasattr(db_obj, 'is_system') and db_obj.is_system:
        raise exc.InvalidActionException(
            "Can not modify a system %s resource, ID: %s" %
            (db_obj.__class__.__name__, db_obj.id)
        )