#!/usr/bin/env python3

# © Copyright 2021-2022, Scott Gasch

"""A simple utility to unpickle some code from the filesystem, run it,
pickle the results, and save them back on the filesystem.  This file
helps :mod:`pyutils.parallelize.parallelize` and
:mod:`pyutils.parallelize.executors` implement the
:class:`pyutils.parallelize.executors.RemoteExecutor` that distributes
work to different machines when code is marked with the
`@parallelize(method=Method.REMOTE)` decorator.

.. warning::
    Please don't unpickle (or run!) code you do not know!  This
    helper is designed to be run with your own code.

See details in :mod:`pyutils.parallelize.parallelize` for instructions
about how to set this up.
"""

import logging
import os
import signal
import sys
import threading
import time
from typing import Optional

import cloudpickle  # type: ignore
import psutil  # type: ignore

from pyutils import argparse_utils, bootstrap, config
from pyutils.parallelize.thread_utils import background_thread
from pyutils.stopwatch import Timer

logger = logging.getLogger(__file__)

cfg = config.add_commandline_args(
    f"Remote Worker ({__file__})",
    "Helper to run pickled code remotely and return results",
)
cfg.add_argument(
    '--code_file',
    type=str,
    required=True,
    metavar='FILENAME',
    help='The location of the bundle of code to execute.',
)
cfg.add_argument(
    '--result_file',
    type=str,
    required=True,
    metavar='FILENAME',
    help='The location where we should write the computation results.',
)
cfg.add_argument(
    '--watch_for_cancel',
    action=argparse_utils.ActionNoYes,
    default=True,
    help='Should we watch for the cancellation of our parent ssh process?',
)


@background_thread
def _watch_for_cancel(terminate_event: threading.Event) -> None:
    logger.debug('Starting up background thread...')
    p = psutil.Process(os.getpid())
    while True:
        saw_sshd = False
        ancestors = p.parents()
        for ancestor in ancestors:
            name = ancestor.name()
            pid = ancestor.pid
            logger.debug('Ancestor process %s (pid=%d)', name, pid)
            if 'ssh' in name.lower():
                saw_sshd = True
                break
        if not saw_sshd:
            logger.error(
                'Did not see sshd in our ancestors list?!  Committing suicide.'
            )
            os.system('pstree')
            os.kill(os.getpid(), signal.SIGTERM)
            time.sleep(5.0)
            os.kill(os.getpid(), signal.SIGKILL)
            sys.exit(-1)
        if terminate_event.is_set():
            return
        time.sleep(1.0)


def _cleanup_and_exit(
    thread: Optional[threading.Thread],
    stop_event: Optional[threading.Event],
    exit_code: int,
) -> None:
    if stop_event is not None:
        stop_event.set()
        assert thread is not None
        thread.join()
    sys.exit(exit_code)


@bootstrap.initialize
def main() -> None:
    """Remote worker entry point."""

    in_file = config.config['code_file']
    assert in_file and type(in_file) == str
    out_file = config.config['result_file']
    assert out_file and type(out_file) == str

    thread = None
    stop_event = None
    if config.config['watch_for_cancel']:
        thread, stop_event = _watch_for_cancel()

    logger.debug('Reading %s.', in_file)
    try:
        with open(in_file, 'rb') as rb:
            serialized = rb.read()
    except Exception as e:
        logger.exception(e)
        logger.critical('Problem reading %s. Aborting.', in_file)
        _cleanup_and_exit(thread, stop_event, 1)

    logger.debug('Deserializing %s', in_file)
    try:
        fun, args, kwargs = cloudpickle.loads(serialized)
    except Exception as e:
        logger.exception(e)
        logger.critical('Problem deserializing %s. Aborting.', in_file)
        _cleanup_and_exit(thread, stop_event, 2)

    logger.debug('Invoking user-defined code...')
    with Timer() as t:
        ret = fun(*args, **kwargs)
    logger.debug('User code took %.1fs', t())

    logger.debug('Serializing results')
    try:
        serialized = cloudpickle.dumps(ret)
    except Exception as e:
        logger.exception(e)
        logger.critical('Could not serialize result (%s). Aborting.', type(ret))
        _cleanup_and_exit(thread, stop_event, 3)

    logger.debug('Writing %s', out_file)
    try:
        with open(out_file, 'wb') as wb:
            wb.write(serialized)
    except Exception as e:
        logger.exception(e)
        logger.critical('Error writing %s. Aborting.', out_file)
        _cleanup_and_exit(thread, stop_event, 4)
    _cleanup_and_exit(thread, stop_event, 0)


if __name__ == '__main__':
    main()