# © 2021 James R Barlow: https://github.com/jbarlow83
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in all
# copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.

"""Alternate executor to support OCRmyPDF in AWS Lambda"""


import logging
import logging.handlers
import signal
import threading
from contextlib import suppress
from enum import Enum, auto
from itertools import islice, repeat, takewhile, zip_longest
from multiprocessing import Pipe, Process
from multiprocessing.connection import Connection, wait
from typing import Callable, Iterable, Optional
from unittest.mock import Mock

from ocrmypdf import hookimpl
from ocrmypdf.exceptions import InputFileError

pool_lock = threading.Lock()


class MessageType(Enum):
    exception = auto()
    result = auto()
    complete = auto()


def split_every(n: int, iterable: Iterable):
    iterator = iter(iterable)
    return takewhile(bool, (list(islice(iterator, n)) for _ in repeat(None)))


def process_sigbus(*args):
    raise InputFileError("A worker process lost access to an input file")


class ConnectionLogHandler(logging.handlers.QueueHandler):
    def __init__(self, conn: Connection) -> None:
        super().__init__(None)
        self.conn = conn

    def enqueue(self, record):
        self.conn.send(('log', record))


def process_loop(
    conn: Connection, user_init: Callable[[], None], loglevel, task, task_args
):
    """Initialize a process pool worker"""

    # 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)

    # Reconfigure the root logger for this process to send all messages to a queue
    h = ConnectionLogHandler(conn)
    root = logging.getLogger()
    root.setLevel(loglevel)
    root.handlers = []
    root.addHandler(h)

    user_init()

    for args in task_args:
        try:
            result = task(args)
        except Exception as e:
            conn.send((MessageType.exception, e))
            break
        else:
            conn.send((MessageType.result, result))

    conn.send((MessageType.complete, None))
    conn.close()
    return


def lambda_pool_impl(
    *,
    use_threads: bool,
    max_workers: int,
    tqdm_kwargs: dict,
    worker_initializer: Callable,
    task: Callable,
    task_arguments: Optional[Iterable] = None,
    task_finished: Callable,
):
    pbar = Mock()

    if use_threads and max_workers == 1:
        for args in task_arguments:
            result = task(args)
            task_finished(result, pbar)
        return

    with pool_lock:
        _lambda_pool_impl(
            max_workers=max_workers,
            worker_initializer=worker_initializer,
            task=task,
            task_arguments=task_arguments,
            task_finished=task_finished,
            pbar=pbar,
        )


def _lambda_pool_impl(
    *,
    max_workers: int,
    worker_initializer: Callable,
    task: Callable,
    task_arguments: Optional[Iterable] = None,
    task_finished: Callable,
    pbar,
):
    task_arguments = list(task_arguments)
    grouped_args = list(zip_longest(*list(split_every(max_workers, task_arguments))))
    if not grouped_args:
        return

    processes = []
    connections = []
    for n in range(max_workers):
        parent_conn, child_conn = Pipe()

        worker_args = [args for args in grouped_args[n] if args is not None]
        process = Process(
            target=process_loop,
            args=(
                child_conn,
                worker_initializer,
                logging.getLogger("").level,
                task,
                worker_args,
            ),
        )
        process.daemon = True
        processes.append(process)
        connections.append(parent_conn)

    for process in processes:
        process.start()

    while connections:
        for r in wait(connections):
            try:
                msg_type, msg = r.recv()
            except EOFError:
                connections.remove(r)
                continue

            if msg_type == MessageType.result:
                if task_finished:
                    task_finished(msg, pbar)
            elif msg_type == 'log':
                record = msg
                logger = logging.getLogger(record.name)
                logger.handle(record)
            elif msg_type == MessageType.complete:
                connections.remove(r)
            elif msg_type == MessageType.exception:
                for process in processes:
                    process.terminate()
                raise msg

    for process in processes:
        process.join()


@hookimpl
def get_parallel_executor():
    return lambda_pool_impl