EDMarketConnector/EDMCLogging.py

"""
This module provides for a common logging-powered log facility.
Mostly it implements a logging.Filter() in order to get two extra
members on the logging.LogRecord instance for use in logging.Formatter()
strings.
"""

# So that any warning about accessing a protected member is only in one place.
from sys import _getframe as getframe
import inspect
import logging
from typing import Tuple


# TODO: Tests:
#
#       1. Call from bare function in file.
#       2. Call from `if __name__ == "__main__":` section
#
#       3. Call from 1st level function in 1st level Class in file
#       4. Call from 2nd level function in 1st level Class in file
#       5. Call from 3rd level function in 1st level Class in file
#
#       6. Call from 1st level function in 2nd level Class in file
#       7. Call from 2nd level function in 2nd level Class in file
#       8. Call from 3rd level function in 2nd level Class in file
#
#       9. Call from 1st level function in 3rd level Class in file
#      10. Call from 2nd level function in 3rd level Class in file
#      11. Call from 3rd level function in 3rd level Class in file
#
#      12. Call from 2nd level file, all as above.
#
#      13. Call from *module*
#
#      14. Call from *package*

_default_loglevel = logging.DEBUG


class Logger:
    """
    Wrapper class for all logging configuration and code.

    Class instantiation requires the 'logger name' and optional loglevel.
    It is intended that this 'logger name' be re-used in all files/modules
    that need to log.

    Users of this class should then call getLogger() to get the
    logging.Logger instance.
    """
    def __init__(self, logger_name: str, loglevel: int = _default_loglevel):
        """
        Set up a `logging.Logger` with our preferred configuration.
        This includes using an EDMCContextFilter to add 'class' and 'qualname'
        expansions for logging.Formatter().
        """
        self.logger = logging.getLogger(logger_name)
        # Configure the logging.Logger
        self.logger.setLevel(loglevel)

        # Set up filter for adding class name
        self.logger_filter = EDMCContextFilter()
        self.logger.addFilter(self.logger_filter)

        self.logger_channel = logging.StreamHandler()
        self.logger_channel.setLevel(loglevel)

        self.logger_formatter = logging.Formatter('%(asctime)s - %(name)s - %(levelname)s - %(module)s.%(qualname)s:%(lineno)d: %(class)s: %(message)s')  # noqa: E501
        self.logger_formatter.default_time_format = '%Y-%m-%d %H:%M:%S'
        self.logger_formatter.default_msec_format = '%s.%03d'

        self.logger_channel.setFormatter(self.logger_formatter)
        self.logger.addHandler(self.logger_channel)

    def get_logger(self) -> logging.Logger:
        """
        :return: The logging.Logger instance.
        """
        return self.logger


def get_plugin_logger(name: str, loglevel: int = _default_loglevel) -> logging.Logger:
    """
    'Found' plugins need their own logger to call out where the logging is
    coming from, but we don't need to set up *everything* for them.

    The name will be '{config.appname}.{plugin.name}', e.g.
    'EDMarketConnector.miggytest'.  This means that any logging sent through
    there *also* goes to the channels defined in the 'EDMarketConnector'
    logger, so we can let that take care of the formatting.

    If we add our own channel then the output gets duplicated (assuming same
    logLevel set).

    However we do need to attach our filter to this still.  That's not at
    the channel level.
    :param name: Name of this Logger.
    :param loglevel: Optional logLevel for this Logger.
    :return: logging.Logger instance, all set up.
    """
    plugin_logger = logging.getLogger(name)
    plugin_logger.setLevel(loglevel)

    plugin_logger.addFilter(EDMCContextFilter())

    return plugin_logger


class EDMCContextFilter(logging.Filter):
    """
    logging.Filter sub-class to place extra attributes of the calling site
    into the record.
    """
    def filter(self, record: logging.LogRecord) -> bool:
        """
        Attempt to set the following in the LogRecord:

            1. class = class name(s) of the call site, if applicable
            2. qualname = __qualname__ of the call site.  This simplifies
             logging.Formatter() as you can use just this no matter if there is
             a class involved or not, so you get a nice clean:
                 <file/module>.<classA>[.classB....].<function>

        If we fail to be able to properly set either then:

            1. Use print() to alert, to be SURE a message is seen.
            2. But also return strings noting the error, so there'll be
             something in the log output if it happens.

        :param record: The LogRecord we're "filtering"
        :return: bool - Always true in order for this record to be logged.
        """
        class_name = qualname = ''
        # Don't even call in if both already set.
        if not getattr(record, 'class', None) or not getattr(record, 'qualname', None):
            (class_name, qualname) = self.caller_class_and_qualname()

        # Only set if not already provided by logging itself
        if getattr(record, 'class', None) is None:
            setattr(record, 'class', class_name)

        # Only set if not already provided by logging itself
        if getattr(record, 'qualname', None) is None:
            setattr(record, 'qualname', qualname)

        return True

    @classmethod
    def caller_class_and_qualname(cls) -> Tuple[str, str]:
        """
        Figure out our caller's class name(s) and qualname

        Ref: <https://gist.github.com/techtonik/2151726#gistcomment-2333747>

        :return: Tuple[str, str]: The caller's class name(s) and qualname
        """
        # Go up through stack frames until we find the first with a
        # type(f_locals.self) of logging.Logger.  This should be the start
        # of the frames internal to logging.
        frame: 'frame' = getframe(0)
        while frame:
            if isinstance(frame.f_locals.get('self'), logging.Logger):
                frame = frame.f_back  # Want to start on the next frame below
                break
            frame = frame.f_back

        # Now continue up through frames until we find the next one where
        # that is *not* true, as it should be the call site of the logger
        # call
        while frame:
            if not isinstance(frame.f_locals.get('self'), logging.Logger):
                break  # We've found the frame we want
            frame = frame.f_back

        caller_qualname = caller_class_names = ''
        if frame:
            # <https://stackoverflow.com/questions/2203424/python-how-to-retrieve-class-information-from-a-frame-object#2220759>
            frame_info = inspect.getframeinfo(frame)
            args, _, _, value_dict = inspect.getargvalues(frame)
            if len(args) and args[0] == 'self':
                frame_class = value_dict['self']

                if frame_class:
                    # Find __qualname__ of the caller
                    fn = getattr(frame_class, frame_info.function)
                    if fn and fn.__qualname__:
                        caller_qualname = fn.__qualname__

                    # Find containing class name(s) of caller, if any
                    if frame_class.__class__ and frame_class.__class__.__qualname__:
                        caller_class_names = frame_class.__class__.__qualname__

            # It's a call from the top level module file
            elif frame_info.function == '<module>':
                caller_class_names = '<none>'
                caller_qualname = value_dict['__name__']

            elif frame_info.function != '':
                caller_class_names = '<none>'
                caller_qualname = frame_info.function

            # https://docs.python.org/3.7/library/inspect.html#the-interpreter-stack
            del frame

        if caller_qualname == '':
            print('ALERT!  Something went wrong with finding caller qualname for logging!')
            caller_qualname = '<ERROR in EDMCLogging.caller_class_and_qualname() for "qualname">'

        if caller_class_names == '':
            print('ALERT!  Something went wrong with finding caller class name(s) for logging!')
            caller_class_names = '<ERROR in EDMCLogging.caller_class_and_qualname() for "class">'

        return caller_class_names, caller_qualname