moment/src/backend/qml_bridge.py

# SPDX-License-Identifier: LGPL-3.0-or-later

"""Install `uvloop` if possible and provide a `QMLBridge`."""

# WARNING: make sure to not top-level import the media_cache module here,
# directly or indirectly via another module import (e.g. backend).
# See https://stackoverflow.com/a/55918049

import asyncio
import logging as log
import signal
import traceback
from concurrent.futures import Future
from operator import attrgetter
from threading import Thread
from typing import Coroutine, Sequence

from .pyotherside_events import CoroutineDone, LoopException

try:
    import uvloop
except ModuleNotFoundError:
    log.warning("uvloop module not found, using slower default asyncio loop")
else:
    uvloop.install()


class QMLBridge:
    """Setup asyncio and provide synchronous methods to call coroutines.

    A thread is created to run the asyncio loop in, to ensure all calls from
    QML return instantly.
    Methods are provided for QML to call coroutines using PyOtherSide, which
    doesn't have this ability out of the box.

    Attributes:
        backend: The `Backend` containing the coroutines of interest and
            `MatrixClient` objects.
    """

    def __init__(self) -> None:
        from .backend import Backend
        self.backend: Backend = Backend()

        self._loop = asyncio.get_event_loop()
        self._loop.set_exception_handler(self._loop_exception_handler)

        Thread(target=self._start_asyncio_loop).start()


    def _loop_exception_handler(
        self, loop: asyncio.AbstractEventLoop, context: dict,
    ) -> None:
        if "exception" in context:
            err   = context["exception"]
            trace = "".join(
                traceback.format_exception(type(err), err, err.__traceback__),
            )
            LoopException(context["message"], err, trace)

        loop.default_exception_handler(context)


    def _start_asyncio_loop(self) -> None:
        asyncio.set_event_loop(self._loop)
        self._loop.run_forever()


    def _call_coro(self, coro: Coroutine, uuid: str) -> Future:
        """Schedule a coroutine to run in our thread and return a `Future`."""

        def on_done(future: Future) -> None:
            """Send a PyOtherSide event with the coro's result/exception."""
            result = exception = trace = None

            try:
                result = future.result()
            except Exception as err:
                exception = err
                trace     = traceback.format_exc().rstrip()

            CoroutineDone(uuid, result, exception, trace)

        future = asyncio.run_coroutine_threadsafe(coro, self._loop)
        future.add_done_callback(on_done)
        return future


    def call_backend_coro(
        self, name: str, uuid: str, args: Sequence[str] = (),
    ) -> Future:
        """Schedule a `Backend` coroutine and return a `Future`."""

        return self._call_coro(attrgetter(name)(self.backend)(*args), uuid)


    def call_client_coro(
        self, user_id: str, name: str, uuid: str, args: Sequence[str] = (),
    ) -> Future:
        """Schedule a `MatrixClient` coroutine and return a `Future`."""

        client = self.backend.clients[user_id]
        return self._call_coro(attrgetter(name)(client)(*args), uuid)


    def pdb(self, additional_data: Sequence = ()) -> None:
        """Call the RemotePdb debugger; define some conveniance variables."""

        ad  = additional_data              # noqa
        ba  = self.backend                 # noqa
        mo  = self.backend.models          # noqa
        cl  = self.backend.clients
        gcl = lambda user: cl[f"@{user}:matrix.org"]  # noqa

        rc = lambda c: asyncio.run_coroutine_threadsafe(c, self._loop)  # noqa

        p = print  # pdb's `p` doesn't print a class's __str__  # noqa
        try:
            from pprintpp import pprint as pp  # noqa
        except ModuleNotFoundError:
            pass

        log.info("\n=> Run `socat readline tcp:127.0.0.1:4444` in a terminal "
                 "to connect to pdb.")
        import remote_pdb
        remote_pdb.RemotePdb("127.0.0.1", 4444).set_trace()


# Make CTRL-C work again
try:
    signal.signal(signal.SIGINT, signal.SIG_DFL)
except ValueError:
    # FIXME - happens when we're imported from a thread,
    # occurs in py3.8 but not 3.6?
    pass

BRIDGE = QMLBridge()