# Copyright 2018-2023 Gentoo Authors
# Distributed under the terms of the GNU General Public License v2

import os
import signal

import asyncio as _real_asyncio
from asyncio.events import AbstractEventLoop as _AbstractEventLoop
from asyncio.unix_events import ThreadedChildWatcher

try:
    from asyncio.unix_events import PidfdChildWatcher
except ImportError:
    PidfdChildWatcher = None

import portage


class AsyncioEventLoop(_AbstractEventLoop):
    """
    Implementation of asyncio.AbstractEventLoop which wraps asyncio's
    event loop and is minimally compatible with _PortageEventLoop.
    """

    def __init__(self, loop=None):
        loop = loop or _real_asyncio.get_event_loop()
        self._loop = loop
        self.run_until_complete = (
            self._run_until_complete
            if portage._internal_caller
            else loop.run_until_complete
        )
        self.call_soon = loop.call_soon
        self.call_soon_threadsafe = loop.call_soon_threadsafe
        self.call_later = loop.call_later
        self.call_at = loop.call_at
        self.is_running = loop.is_running
        self.is_closed = loop.is_closed
        self.close = loop.close
        self.create_future = (
            loop.create_future
            if hasattr(loop, "create_future")
            else self._create_future
        )
        self.create_task = loop.create_task
        self.add_reader = loop.add_reader
        self.remove_reader = loop.remove_reader
        self.add_writer = loop.add_writer
        self.remove_writer = loop.remove_writer
        self.run_in_executor = loop.run_in_executor
        self.time = loop.time
        self.default_exception_handler = loop.default_exception_handler
        self.call_exception_handler = loop.call_exception_handler
        self.set_debug = loop.set_debug
        self.get_debug = loop.get_debug
        self._wakeup_fd = -1
        self._child_watcher = None

        if portage._internal_caller:
            loop.set_exception_handler(self._internal_caller_exception_handler)

    @staticmethod
    def _internal_caller_exception_handler(loop, context):
        """
        An exception handler which drops to a pdb shell if std* streams
        refer to a tty, and otherwise kills the process with SIGTERM.

        In order to avoid potential interference with API consumers, this
        implementation is only used when portage._internal_caller is True.
        """
        loop.default_exception_handler(context)
        if "exception" in context:
            # Normally emerge will wait for all coroutines to complete
            # after SIGTERM has been received. However, an unhandled
            # exception will prevent the interrupted coroutine from
            # completing, therefore use the default SIGTERM handler
            # in order to ensure that emerge exits immediately (though
            # uncleanly).
            signal.signal(signal.SIGTERM, signal.SIG_DFL)
            os.kill(portage.getpid(), signal.SIGTERM)

    def _create_future(self):
        """
        Provide AbstractEventLoop.create_future() for python3.4.
        """
        return _real_asyncio.Future(loop=self._loop)

    @property
    def _asyncio_child_watcher(self):
        """
        Portage internals use this as a layer of indirection for
        asyncio.get_child_watcher(), in order to support versions of
        python where asyncio is not available.

        @rtype: asyncio.AbstractChildWatcher
        @return: the internal event loop's AbstractChildWatcher interface
        """
        if self._child_watcher is None:
            pidfd_works = False
            if PidfdChildWatcher is not None and hasattr(os, "pidfd_open"):
                try:
                    fd = os.pidfd_open(portage.getpid())
                except Exception:
                    pass
                else:
                    os.close(fd)
                    pidfd_works = True

            if pidfd_works:
                watcher = PidfdChildWatcher()
            else:
                watcher = ThreadedChildWatcher()

            watcher.attach_loop(self._loop)
            self._child_watcher = _ChildWatcherThreadSafetyWrapper(self, watcher)

        return self._child_watcher

    @property
    def _asyncio_wrapper(self):
        """
        Portage internals use this as a layer of indirection in cases
        where a wrapper around an asyncio.AbstractEventLoop implementation
        is needed for purposes of compatibility.

        @rtype: asyncio.AbstractEventLoop
        @return: the internal event loop's AbstractEventLoop interface
        """
        return self

    def _run_until_complete(self, future):
        """
        An implementation of AbstractEventLoop.run_until_complete that suppresses
        spurious error messages like the following reported in bug 655656:

            Exception ignored when trying to write to the signal wakeup fd:
            BlockingIOError: [Errno 11] Resource temporarily unavailable

        In order to avoid potential interference with API consumers, this
        implementation is only used when portage._internal_caller is True.
        """
        if self._wakeup_fd != -1:
            signal.set_wakeup_fd(self._wakeup_fd)
            self._wakeup_fd = -1
            # Account for any signals that may have arrived between
            # set_wakeup_fd calls.
            os.kill(portage.getpid(), signal.SIGCHLD)
        try:
            return self._loop.run_until_complete(future)
        finally:
            try:
                self._wakeup_fd = signal.set_wakeup_fd(-1)
            except ValueError:
                # This is intended to fail when not called in the main thread.
                pass


class _ChildWatcherThreadSafetyWrapper:
    """
    This class provides safety if multiple loops are running in different threads.
    """

    def __init__(self, loop, real_watcher):
        self._loop = loop
        self._real_watcher = real_watcher

    def close(self):
        pass

    def __enter__(self):
        return self

    def __exit__(self, a, b, c):
        pass

    def _child_exit(self, pid, status, callback, *args):
        self._loop.call_soon_threadsafe(callback, pid, status, *args)

    def add_child_handler(self, pid, callback, *args):
        self._real_watcher.add_child_handler(pid, self._child_exit, callback, *args)

    def remove_child_handler(self, pid):
        return self._real_watcher.remove_child_handler(pid)
