# Code to implement asynchronous logging from a background thread
#
# Copyright (C) 2016-2019  Kevin O'Connor <kevin@koconnor.net>
#
# This file may be distributed under the terms of the GNU GPLv3 license.
import logging
import logging.handlers
import queue
import threading
import time


# Class to forward all messages through a queue to a background thread
class QueueHandler(logging.Handler):
    def __init__(self, queue):
        logging.Handler.__init__(self)
        self.queue = queue

    def emit(self, record):
        try:
            self.format(record)
            record.msg = record.message
            record.args = None
            record.exc_info = None
            self.queue.put_nowait(record)
        except Exception:
            self.handleError(record)


# Class to poll a queue in a background thread and log each message
class QueueListener(logging.StreamHandler):
    def __init__(self):
        super().__init__()
        self.bg_queue = queue.Queue()
        self.bg_thread = threading.Thread(target=self._bg_thread)
        self.bg_thread.start()

    def _bg_thread(self):
        while True:
            record = self.bg_queue.get(True)
            if record is None:
                break
            self.handle(record)

    def stop(self):
        self.bg_queue.put_nowait(None)
        self.bg_thread.join()


MainQueueHandler = None


def setup_bg_logging(debuglevel):
    global MainQueueHandler
    ql = QueueListener()
    MainQueueHandler = QueueHandler(ql.bg_queue)
    root = logging.getLogger()
    root.addHandler(MainQueueHandler)
    root.setLevel(debuglevel)
    return ql


def clear_bg_logging():
    global MainQueueHandler
    if MainQueueHandler is not None:
        root = logging.getLogger()
        root.removeHandler(MainQueueHandler)
        root.setLevel(logging.WARNING)
        MainQueueHandler = None