# SPDX-FileCopyrightText: 2022 James R. Barlow
# SPDX-License-Identifier: MPL-2.0
"""OCRmyPDF's multiprocessing/multithreading abstraction layer."""

from __future__ import annotations

import logging
import logging.handlers
import multiprocessing
import multiprocessing.queues
import os
import queue
import signal
import sys
import threading
from collections.abc import Callable, Iterable
from concurrent.futures import ProcessPoolExecutor, ThreadPoolExecutor, as_completed
from contextlib import suppress
from typing import TYPE_CHECKING

from rich.console import Console as RichConsole

from ocrmypdf import Executor, hookimpl
from ocrmypdf._logging import RichLoggingHandler
from ocrmypdf._progressbar import RichProgressBar
from ocrmypdf.exceptions import InputFileError
from ocrmypdf.helpers import remove_all_log_handlers

if TYPE_CHECKING:
    from typing import TypeAlias

    Queue: TypeAlias = multiprocessing.queues.Queue | queue.Queue
    UserInit: TypeAlias = Callable[[], None]
    WorkerInit: TypeAlias = Callable[[Queue, UserInit, int], None]

FuturesExecutorClass = type[ThreadPoolExecutor] | type[ProcessPoolExecutor]


def log_listener(q: Queue):
    """Listen to the worker processes and forward the messages to logging.

    For simplicity this is a thread rather than a process. Only one process
    should actually write to sys.stderr or whatever we're using, so if this is
    made into a process the main application needs to be directed to it.

    See:
    https://docs.python.org/3/howto/logging-cookbook.html#logging-to-a-single-file-from-multiple-processes
    """
    while True:
        try:
            record = q.get()
            if record is None:
                break
            logger = logging.getLogger(record.name)
            logger.handle(record)
        except Exception:  # pylint: disable=broad-except
            import traceback  # pylint: disable=import-outside-toplevel

            print("Logging problem", file=sys.stderr)
            traceback.print_exc(file=sys.stderr)


def process_sigbus(*args):
    """Handle SIGBUS signal at the worker level."""
    raise InputFileError("A worker process lost access to an input file")


def process_init(q: Queue, user_init: UserInit, loglevel) -> None:
    """Initialize a process pool worker."""
    # Ignore SIGINT (our parent process will kill us gracefully)
    signal.signal(signal.SIGINT, signal.SIG_IGN)

    # Install SIGBUS handler (so our parent process can abort somewhat gracefully)
    with suppress(AttributeError):  # Windows and Cygwin do not have SIGBUS
        # Windows and Cygwin do not have pthread_sigmask or SIGBUS
        signal.signal(signal.SIGBUS, process_sigbus)

    # Remove any log handlers inherited from the parent process
    root = logging.getLogger()
    remove_all_log_handlers(root)

    # Set up our single log handler to forward messages to the parent
    root.setLevel(loglevel)
    root.addHandler(logging.handlers.QueueHandler(q))

    user_init()
    return


def thread_init(q: Queue, user_init: UserInit, loglevel) -> None:
    """Begin a thread pool worker."""
    del q  # unused but required argument
    del loglevel  # unused but required argument
    # As a thread, block SIGBUS so the main thread deals with it...
    with suppress(AttributeError):
        signal.pthread_sigmask(signal.SIG_BLOCK, {signal.SIGBUS})

    user_init()
    return


def setup_executor(use_threads: bool) -> tuple[Queue, Executor, WorkerInit]:
    if not use_threads:
        # Some execution environments like AWS Lambda and Termux do not support
        # semaphores. Check if semaphore support is available, and if not, fall back
        # to using threads.
        try:
            # pylint: disable=import-outside-toplevel
            from multiprocessing.synchronize import SemLock

            del SemLock
        except ImportError:
            use_threads = True

    if use_threads:
        loq_queue = queue.Queue(-1)
        executor_class = ThreadPoolExecutor
        initializer = thread_init
    else:
        loq_queue = multiprocessing.Queue(-1)
        executor_class = ProcessPoolExecutor
        initializer = process_init

    return loq_queue, executor_class, initializer


class StandardExecutor(Executor):
    """Standard OCRmyPDF concurrent task executor."""

    def _execute(
        self,
        *,
        use_threads: bool,
        max_workers: int,
        progress_kwargs: dict,
        worker_initializer: Callable,
        task: Callable,
        task_arguments: Iterable,
        task_finished: Callable,
    ):
        log_queue, executor_class, initializer = setup_executor(use_threads)

        # Regardless of whether we use_threads for worker processes, the log_listener
        # must be a thread. Make sure we create the listener after the worker pool,
        # so that it does not get forked into the workers.
        # If use_threads is False, we are currently guilty of creating a thread before
        # forking on Linux, which is not recommended. However, we take a big
        # performance hit in pdfinfo if we can't fork. Long term solution is to
        # replace most of this with an asyncio implementation, and probably to
        # migrate some of pdfinfo into C++ or Rust.
        listener = threading.Thread(target=log_listener, args=(log_queue,))
        listener.start()

        with (
            self.pbar_class(**progress_kwargs) as pbar,
            executor_class(
                max_workers=max_workers,
                initializer=initializer,
                initargs=(log_queue, worker_initializer, logging.getLogger("").level),
            ) as executor,
        ):
            futures = [executor.submit(task, *args) for args in task_arguments]
            try:
                for future in as_completed(futures):
                    result = future.result()
                    task_finished(result, pbar)
            except KeyboardInterrupt:
                # Terminate pool so we exit instantly
                executor.shutdown(wait=False, cancel_futures=True)
                raise
            except Exception:
                if not os.environ.get("PYTEST_CURRENT_TEST", ""):
                    # Normally we shutdown without waiting for other child workers
                    # on error, because there is no point in waiting for them. Their
                    # results will be discard. But if the condition above is True,
                    # then we are running in pytest, and we want everything to exit
                    # as cleanly as possible so that we get good error messages.
                    executor.shutdown(wait=False, cancel_futures=True)
                raise
            finally:
                # Terminate log listener
                log_queue.put_nowait(None)

        # When the above succeeds, wait for the listener thread to exit. (If
        # an exception occurs, we don't try to join, in case it deadlocks.)
        listener.join()


@hookimpl
def get_executor(progressbar_class):
    """Return the default executor."""
    return StandardExecutor(pbar_class=progressbar_class)


RICH_CONSOLE = RichConsole(stderr=True)


@hookimpl
def get_progressbar_class():
    """Return the default progress bar class."""

    def partial_RichProgressBar(*args, **kwargs):
        return RichProgressBar(*args, **kwargs, console=RICH_CONSOLE)

    return partial_RichProgressBar


@hookimpl
def get_logging_console():
    """Return the default logging console handler."""
    return RichLoggingHandler(console=RICH_CONSOLE)
