Python backend "App" becomes QmlBridge

Is now strictly about setting up asyncio/uvloop and providing the
functions for QML to interact with it and call backend coroutines.

The appdirs attribute is moved to Backend.

src/backend/qml_bridge.py

@@ -0,0 +1,94 @@
+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 .backend import Backend
+from .pyotherside_events import CoroutineDone
+
+try:
+    import uvloop
+except ModuleNotFoundError:
+    log.warning("uvloop module not found, using slower default asyncio loop")
+else:
+    uvloop.install()
+
+
+class QmlBridge:
+    def __init__(self) -> None:
+        self.backend = Backend()
+
+        self.loop = asyncio.get_event_loop()
+        Thread(target=self._start_loop_in_thread).start()
+
+
+    def _start_loop_in_thread(self) -> None:
+        asyncio.set_event_loop(self.loop)
+        self.loop.run_forever()
+
+
+    def _run_coro_in_loop(self, coro: Coroutine) -> Future:
+        return asyncio.run_coroutine_threadsafe(coro, self.loop)
+
+
+    def _call_coro(self, coro: Coroutine, uuid: str) -> Future:
+        def on_done(future: Future) -> None:
+            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 = self._run_coro_in_loop(coro)
+        future.add_done_callback(on_done)
+        return future
+
+
+    def call_backend_coro(
+        self, name: str, uuid: str, args: Sequence[str] = (),
+    ) -> 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:
+
+        client = self.backend.clients[user_id]
+        return self._call_coro(attrgetter(name)(client)(*args), uuid)
+
+
+    def pdb(self, additional_data: Sequence = ()) -> None:
+        ad  = additional_data              # noqa
+        rc  = self._run_coro_in_loop       # noqa
+        ba  = self.backend                 # noqa
+        mo  = self.backend.models          # noqa
+        cl  = self.backend.clients
+        gcl = lambda user: cl[f"@{user}:matrix.org"]  # noqa
+
+        from .models.items import Account, Room, Member, Event, Device  # 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
+signal.signal(signal.SIGINT, signal.SIG_DFL)
+
+BRIDGE = QmlBridge()