"""This module sets up use of the Python logging module by the agent. As
we don't want to rely exclusively on the user having configured the
logging module themselves to capture any logged output we attach our own
log file when enabled from agent configuration. We also provide ability
to fallback to using stdout or stderr.

"""

import os
import sys
import logging
import threading

_lock = threading.Lock()

class _NullHandler(logging.Handler):
    def emit(self, record):
        pass

_agent_logger = logging.getLogger('newrelic')
_agent_logger.addHandler(_NullHandler())

_LOG_FORMAT = '%(asctime)s (%(process)d/%(threadName)s) ' \
              '%(name)s %(levelname)s - %(message)s'

_initialized = False

def _initialize_stdout_logging(log_level):
    handler = logging.StreamHandler(sys.stdout)

    formatter = logging.Formatter(_LOG_FORMAT)
    handler.setFormatter(formatter)

    _agent_logger.addHandler(handler)
    _agent_logger.setLevel(log_level)

    _agent_logger.debug('Initializing Python agent stdout logging.')

def _initialize_stderr_logging(log_level):
    handler = logging.StreamHandler(sys.stderr)

    formatter = logging.Formatter(_LOG_FORMAT)
    handler.setFormatter(formatter)

    _agent_logger.addHandler(handler)
    _agent_logger.setLevel(log_level)

    _agent_logger.debug('Initializing Python agent stderr logging.')

def _initialize_file_logging(log_file, log_level):
    handler = logging.FileHandler(log_file)

    formatter = logging.Formatter(_LOG_FORMAT)
    handler.setFormatter(formatter)

    _agent_logger.addHandler(handler)
    _agent_logger.setLevel(log_level)

    _agent_logger.debug('Initializing Python agent logging.')
    _agent_logger.debug('Log file "%s".' % log_file)

def initialize_logging(log_file, log_level):
    global _initialized

    if _initialized:
        return

    _lock.acquire()

    try:
        if log_file == 'stdout':
            _initialize_stdout_logging(log_level)

        elif log_file == 'stderr':
            _initialize_stderr_logging(log_level)

        elif log_file:
            try:
                _initialize_file_logging(log_file, log_level)

            except Exception:
                _initialize_stderr_logging(log_level)

                _agent_logger.exception('Falling back to stderr logging as '
                        'unable to create log file %r.' % log_file)

        _initialized = True

    finally:
        _lock.release()

# This is to filter out the overly verbose log messages at INFO level
# made by the urllib3 module embedded in the bundled requests module.

class RequestsConnectionFilter(logging.Filter):
    def filter(self, record):
        return False

_requests_logger = logging.getLogger(
    'newrelic.packages.requests.packages.urllib3.connectionpool')
_requests_logger.addFilter(RequestsConnectionFilter())