import threading
from contextlib import contextmanager
from logging import LogRecord, Logger
from queue import Queue
from typing import Optional, Generator


@contextmanager
def log_combiner_thread(
    *,
    source: Queue[Optional[LogRecord]],
    destination: Logger,
) -> Generator[threading.Thread, None, None]:
    """
    Create a thread that consumes log messages from a multiprocessing queue and sends them to a logger.

    See https://docs.python.org/3/howto/logging-cookbook.html#logging-to-a-single-file-from-multiple-processes

    Args:
        source: The queue to consume from.
        destination: The logger to send messages to.
    """
    thread = threading.Thread(
        target=consume_logging_queue,
        kwargs=dict(
            source=source,
            destination=destination,
        ),
    )
    try:
        thread.start()
        yield thread
    finally:
        destination.debug("Waiting for multiprocess logging thread to stop...")
        source.put(None)  # This tells the logging thread to stop.
        thread.join()  # Wait for the logging thread to stop.
        destination.debug("Multiprocess logging thread stopped.")


def consume_logging_queue(
    *,
    source: Queue[Optional[LogRecord]],
    destination: Logger,
) -> None:
    """
    Consume log messages from a multiprocessing queue and send them to a logger.

    See https://docs.python.org/3/howto/logging-cookbook.html#logging-to-a-single-file-from-multiple-processes

    Args:
        source: The queue to consume from.
        destination: The logger to send messages to.
    """
    while True:
        # This blocks until a record is available.
        record = source.get()

        # We send `None` as a sentinel to tell this function to stop.
        if record is None:
            break

        destination.handle(record)