# Copyright 2016 Google LLC
#
# 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.

"""Python :mod:`logging` handlers for Stackdriver Logging."""

import logging

from google.cloud.logging.handlers.transports import BackgroundThreadTransport
from google.cloud.logging.logger import _GLOBAL_RESOURCE

DEFAULT_LOGGER_NAME = 'python'

EXCLUDED_LOGGER_DEFAULTS = (
    'google.cloud',
    'google.auth',
    'google_auth_httplib2',
)


class CloudLoggingHandler(logging.StreamHandler):
    """Handler that directly makes Stackdriver logging API calls.

    This is a Python standard ``logging`` handler using that can be used to
    route Python standard logging messages directly to the Stackdriver
    Logging API.

    This handler is used when not in GAE or GKE environment.

    This handler supports both an asynchronous and synchronous transport.

    :type client: :class:`google.cloud.logging.client`
    :param client: the authenticated Google Cloud Logging client for this
                   handler to use

    :type name: str
    :param name: the name of the custom log in Stackdriver Logging. Defaults
                 to 'python'. The name of the Python logger will be represented
                 in the ``python_logger`` field.

    :type transport: :class:`type`
    :param transport: Class for creating new transport objects. It should
                      extend from the base :class:`.Transport` type and
                      implement :meth`.Transport.send`. Defaults to
                      :class:`.BackgroundThreadTransport`. The other
                      option is :class:`.SyncTransport`.

    :type resource: :class:`~google.cloud.logging.resource.Resource`
    :param resource: (Optional) Monitored resource of the entry, defaults
                     to the global resource type.

    :type labels: dict
    :param labels: (Optional) Mapping of labels for the entry.

    Example:

    .. code-block:: python

        import logging
        import google.cloud.logging
        from google.cloud.logging.handlers import CloudLoggingHandler

        client = google.cloud.logging.Client()
        handler = CloudLoggingHandler(client)

        cloud_logger = logging.getLogger('cloudLogger')
        cloud_logger.setLevel(logging.INFO)
        cloud_logger.addHandler(handler)

        cloud_logger.error('bad news')  # API call

    """

    def __init__(self, client,
                 name=DEFAULT_LOGGER_NAME,
                 transport=BackgroundThreadTransport,
                 resource=_GLOBAL_RESOURCE,
                 labels=None):
        super(CloudLoggingHandler, self).__init__()
        self.name = name
        self.client = client
        self.transport = transport(client, name)
        self.resource = resource
        self.labels = labels

    def emit(self, record):
        """Actually log the specified logging record.

        Overrides the default emit behavior of ``StreamHandler``.

        See https://docs.python.org/2/library/logging.html#handler-objects

        :type record: :class:`logging.LogRecord`
        :param record: The record to be logged.
        """
        message = super(CloudLoggingHandler, self).format(record)
        self.transport.send(
            record,
            message,
            resource=self.resource,
            labels=self.labels)


def setup_logging(handler, excluded_loggers=EXCLUDED_LOGGER_DEFAULTS,
                  log_level=logging.INFO):
    """Attach a logging handler to the Python root logger

    Excludes loggers that this library itself uses to avoid
    infinite recursion.

    :type handler: :class:`logging.handler`
    :param handler: the handler to attach to the global handler

    :type excluded_loggers: tuple
    :param excluded_loggers: (Optional) The loggers to not attach the handler
                             to. This will always include the loggers in the
                             path of the logging client itself.

    :type log_level: int
    :param log_level: (Optional) Python logging log level. Defaults to
                      :const:`logging.INFO`.

    Example:

    .. code-block:: python

        import logging
        import google.cloud.logging
        from google.cloud.logging.handlers import CloudLoggingHandler

        client = google.cloud.logging.Client()
        handler = CloudLoggingHandler(client)
        google.cloud.logging.handlers.setup_logging(handler)
        logging.getLogger().setLevel(logging.DEBUG)

        logging.error('bad news')  # API call

    """
    all_excluded_loggers = set(excluded_loggers + EXCLUDED_LOGGER_DEFAULTS)
    logger = logging.getLogger()
    logger.setLevel(log_level)
    logger.addHandler(handler)
    logger.addHandler(logging.StreamHandler())
    for logger_name in all_excluded_loggers:
        logger = logging.getLogger(logger_name)
        logger.propagate = False
        logger.addHandler(logging.StreamHandler())
