#!/usr/bin/env python3

# © Copyright 2021-2023, 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 isinstance(in_file, str)
    out_file = config.config["result_file"]
    assert out_file and isinstance(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:
        logger.exception("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:
        logger.exception("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:
        logger.exception("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:
        logger.exception("Error writing %s. Aborting.", out_file)
        _cleanup_and_exit(thread, stop_event, 4)
    _cleanup_and_exit(thread, stop_event, 0)


if __name__ == "__main__":
    main()