Refactor Cocoa stuff into a 'receiver'

The idea here is that there are other places that might want to know
what's playing, besides MPNowPlayingInfoCenter. For example, to expose
the now playing info to Übersicht efficiently, it needs to be available
from a web browser, ideally using WebSockets. So there could be a
receiver that runs a small WebSockets server and sends out now playing
info to anyone who connects.

Additionally, I hope to write receivers for MPRIS and for the System
Media Transport Controls on Windows, making mpd-now-playable equally
useful across all platforms.

None of this is implemented yet, of course, but I hope to get the
WebSockets receiver done pretty soon!

I'm going to keep the default behaviour unchanged. Unless you
explicitly configure different receivers in config.toml,
mpd-now-playable will just behave as an MPNowPlayingInfoCenter
integration as it's always done.

pyproject.toml

@@ -70,6 +70,7 @@ select = [
 ]
 ignore = [
     "ANN101", # missing-type-self
+    "ANN102", # missing-type-cls
 ]
 
 [tool.ruff.lint.flake8-annotations]

schemata/config-v1.json

@@ -1,5 +1,20 @@
 {
 	"$defs": {
+		"CocoaReceiverConfig": {
+			"properties": {
+				"kind": {
+					"const": "cocoa",
+					"default": "cocoa",
+					"enum": [
+						"cocoa"
+					],
+					"title": "Kind",
+					"type": "string"
+				}
+			},
+			"title": "CocoaReceiverConfig",
+			"type": "object"
+		},
 		"MpdConfig": {
 			"properties": {
 				"host": {
@@ -40,6 +55,28 @@
 		},
 		"mpd": {
 			"$ref": "#/$defs/MpdConfig"
+		},
+		"receivers": {
+			"default": [
+				{
+					"kind": "cocoa"
+				}
+			],
+			"items": {
+				"discriminator": {
+					"mapping": {
+						"cocoa": "#/$defs/CocoaReceiverConfig"
+					},
+					"propertyName": "kind"
+				},
+				"oneOf": [
+					{
+						"$ref": "#/$defs/CocoaReceiverConfig"
+					}
+				]
+			},
+			"title": "Receivers",
+			"type": "array"
 		}
 	},
 	"title": "Config",

src/mpd_now_playable/cli.py

@@ -1,30 +1,41 @@
 import asyncio
+from collections.abc import Iterable
 
-from corefoundationasyncio import CoreFoundationEventLoop
 from rich import print
 
 from .__version__ import __version__
-from .cocoa.now_playing import CocoaNowPlaying
 from .config.load import loadConfig
+from .config.model import Config
 from .mpd.listener import MpdStateListener
+from .song_receiver import (
+	Receiver,
+	choose_loop_factory,
+	import_receiver,
+)
 
 
-async def listen() -> None:
-	print(f"mpd-now-playable v{__version__}")
-	config = loadConfig()
-	print(config)
-	listener = MpdStateListener(config.cache)
-	now_playing = CocoaNowPlaying(listener)
+async def listen(
+	config: Config, listener: MpdStateListener, receiver_types: Iterable[type[Receiver]]
+) -> None:
 	await listener.start(config.mpd)
-	await listener.loop(now_playing)
-
-
-def make_loop() -> CoreFoundationEventLoop:
-	return CoreFoundationEventLoop(console_app=True)
+	receivers = (rec(listener, config) for rec in receiver_types)
+	await listener.loop(receivers)
 
 
 def main() -> None:
-	asyncio.run(listen(), loop_factory=make_loop, debug=True)
+	print(f"mpd-now-playable v{__version__}")
+	config = loadConfig()
+	print(config)
+
+	listener = MpdStateListener(config.cache)
+	receiver_types = tuple(import_receiver(rec) for rec in config.receivers)
+
+	factory = choose_loop_factory(receiver_types)
+	asyncio.run(
+		listen(config, listener, receiver_types),
+		loop_factory=factory.make_loop,
+		debug=True,
+	)
 
 
 if __name__ == "__main__":

src/mpd_now_playable/config/model.py

@@ -1,10 +1,33 @@
 from dataclasses import dataclass, field
-from typing import Optional
+from typing import Annotated, Literal, Optional, Protocol
+
+from pydantic import Field
 
 from ..tools.schema.define import schema
 from .fields import Host, Password, Port, Url
 
-__all__ = ("MpdConfig", "Config")
+__all__ = (
+	"Config",
+	"MpdConfig",
+	"BaseReceiverConfig",
+	"CocoaReceiverConfig",
+)
+
+
+class BaseReceiverConfig(Protocol):
+	@property
+	def kind(self) -> str: ...
+
+
+@dataclass(slots=True)
+class CocoaReceiverConfig(BaseReceiverConfig):
+	kind: Literal["cocoa"] = "cocoa"
+
+
+ReceiverConfig = Annotated[
+	CocoaReceiverConfig,
+	Field(discriminator="kind"),
+]
 
 
 @dataclass(slots=True)
@@ -27,3 +50,4 @@ class Config:
 	#: protocols are memory://, redis://, and memcached://.
 	cache: Optional[Url] = None
 	mpd: MpdConfig = field(default_factory=MpdConfig)
+	receivers: tuple[ReceiverConfig, ...] = (CocoaReceiverConfig(),)

src/mpd_now_playable/mpd/listener.py

@@ -1,4 +1,5 @@
 import asyncio
+from collections.abc import Iterable
 from pathlib import Path
 from uuid import UUID
 
@@ -9,7 +10,8 @@ from yarl import URL
 
 from ..config.model import MpdConfig
 from ..player import Player
-from ..song import Artwork, PlaybackState, Song, SongListener, to_artwork
+from ..song import Artwork, PlaybackState, Song, to_artwork
+from ..song_receiver import Receiver
 from ..tools.types import convert_if_exists, un_maybe_plural
 from .artwork_cache import MpdArtworkCache
 from .types import CurrentSongResponse, StatusResponse
@@ -43,7 +45,7 @@ def mpd_current_to_song(
 
 class MpdStateListener(Player):
 	client: MPDClient
-	listener: SongListener
+	receivers: Iterable[Receiver]
 	art_cache: MpdArtworkCache
 	idle_count = 0
 
@@ -62,18 +64,18 @@ class MpdStateListener(Player):
 		print(f"Connected to MPD v{self.client.mpd_version}")
 
 	async def refresh(self) -> None:
-		await self.update_listener(self.listener)
+		await self.update_receivers()
 
-	async def loop(self, listener: SongListener) -> None:
-		self.listener = listener
-		# notify our listener of the initial state MPD is in when this script loads up.
-		await self.update_listener(listener)
+	async def loop(self, receivers: Iterable[Receiver]) -> None:
+		self.receivers = receivers
+		# notify our receivers of the initial state MPD is in when this script loads up.
+		await self.update_receivers()
 		# then wait for stuff to change in MPD. :)
 		async for _ in self.client.idle():
 			self.idle_count += 1
-			await self.update_listener(listener)
+			await self.update_receivers()
 
-	async def update_listener(self, listener: SongListener) -> None:
+	async def update_receivers(self) -> None:
 		# If any async calls in here take long enough that we got another MPD idle event, we want to bail out of this older update.
 		starting_idle_count = self.idle_count
 		status, current = await asyncio.gather(
@@ -85,7 +87,8 @@ class MpdStateListener(Player):
 
 		if status["state"] == "stop":
 			print("Nothing playing")
-			listener.update(None)
+			for r in self.receivers:
+				r.update(None)
 			return
 
 		art = await self.art_cache.get_cached_artwork(current)
@@ -94,7 +97,8 @@ class MpdStateListener(Player):
 
 		song = mpd_current_to_song(status, current, to_artwork(art))
 		rprint(song)
-		listener.update(song)
+		for r in self.receivers:
+			r.update(song)
 
 	async def get_art(self, file: str) -> bytes | None:
 		picture = await self.readpicture(file)

src/mpd_now_playable/receivers/cocoa/__init__.py

@@ -0,0 +1,3 @@
+__all__ = ("receiver",)
+
+from .now_playing import CocoaNowPlayingReceiver as receiver

src/mpd_now_playable/receivers/cocoa/now_playing.py

@@ -1,7 +1,9 @@
 from collections.abc import Callable, Coroutine
 from pathlib import Path
+from typing import Literal
 
 from AppKit import NSCompositingOperationCopy, NSImage, NSMakeRect
+from corefoundationasyncio import CoreFoundationEventLoop
 from Foundation import CGSize, NSMutableDictionary
 from MediaPlayer import (
 	MPChangePlaybackPositionCommandEvent,
@@ -35,9 +37,11 @@ from MediaPlayer import (
 	MPRemoteCommandHandlerStatusSuccess,
 )
 
-from ..player import Player
-from ..song import PlaybackState, Song
-from ..tools.asyncio import run_background_task
+from ...config.model import Config
+from ...player import Player
+from ...song import PlaybackState, Song
+from ...song_receiver import LoopFactory, Receiver
+from ...tools.asyncio import run_background_task
 from .persistent_id import song_to_persistent_id
 
 
@@ -127,8 +131,22 @@ def nothing_to_media_item() -> NSMutableDictionary:
 MPD_LOGO = ns_image_to_media_item_artwork(logo_to_ns_image())
 
 
-class CocoaNowPlaying:
-	def __init__(self, player: Player):
+class CocoaLoopFactory(LoopFactory[CoreFoundationEventLoop]):
+	@property
+	def is_replaceable(self) -> Literal[False]:
+		return False
+
+	@classmethod
+	def make_loop(cls) -> CoreFoundationEventLoop:
+		return CoreFoundationEventLoop(console_app=True)
+
+
+class CocoaNowPlayingReceiver(Receiver):
+	@classmethod
+	def loop_factory(cls) -> LoopFactory[CoreFoundationEventLoop]:
+		return CocoaLoopFactory()
+
+	def __init__(self, player: Player, config: Config):
 		self.cmd_center = MPRemoteCommandCenter.sharedCommandCenter()
 		self.info_center = MPNowPlayingInfoCenter.defaultCenter()
 

src/mpd_now_playable/receivers/cocoa/persistent_id.py

@@ -3,7 +3,7 @@ from pathlib import Path
 from typing import Final
 from uuid import UUID
 
-from ..song import Song
+from ...song import Song
 
 # The maximum size for a BLAKE2b "person" value is sixteen bytes, so we need to be concise.
 HASH_PERSON_PREFIX: Final = b"mnp.mac."

src/mpd_now_playable/song.py

@@ -1,7 +1,7 @@
 from dataclasses import dataclass, field
 from enum import StrEnum
 from pathlib import Path
-from typing import Literal, Protocol
+from typing import Literal
 from uuid import UUID
 
 from pydantic.type_adapter import TypeAdapter
@@ -53,7 +53,3 @@ class Song:
 	duration: float
 	elapsed: float
 	art: Artwork
-
-
-class SongListener(Protocol):
-	def update(self, song: Song | None) -> None: ...

src/mpd_now_playable/song_receiver.py

@@ -0,0 +1,76 @@
+from asyncio import AbstractEventLoop, new_event_loop
+from dataclasses import dataclass
+from importlib import import_module
+from typing import Generic, Iterable, Literal, Protocol, TypeVar, cast
+
+from .config.model import BaseReceiverConfig, Config
+from .player import Player
+from .song import Song
+from .tools.types import not_none
+
+T = TypeVar("T", bound=AbstractEventLoop, covariant=True)
+
+
+class LoopFactory(Generic[T], Protocol):
+	@property
+	def is_replaceable(self) -> bool: ...
+
+	@classmethod
+	def make_loop(cls) -> T: ...
+
+
+class Receiver(Protocol):
+	def __init__(self, player: Player, config: Config) -> None: ...
+	@classmethod
+	def loop_factory(cls) -> LoopFactory[AbstractEventLoop]: ...
+	def update(self, song: Song | None) -> None: ...
+
+
+class ReceiverModule(Protocol):
+	receiver: type[Receiver]
+
+
+class DefaultLoopFactory(LoopFactory[AbstractEventLoop]):
+	@property
+	def is_replaceable(self) -> Literal[True]:
+		return True
+
+	@classmethod
+	def make_loop(cls) -> AbstractEventLoop:
+		return new_event_loop()
+
+
+@dataclass
+class IncompatibleReceiverError(Exception):
+	a: type[Receiver]
+	b: type[Receiver]
+
+
+def import_receiver(config: BaseReceiverConfig) -> type[Receiver]:
+	mod = cast(
+		ReceiverModule, import_module(f"mpd_now_playable.receivers.{config.kind}")
+	)
+	return mod.receiver
+
+
+def choose_loop_factory(
+	receivers: Iterable[type[Receiver]],
+) -> LoopFactory[AbstractEventLoop]:
+	"""Given the desired receivers, determine which asyncio event loop implementation will support all of them. Will raise an IncompatibleReceiverError if no such implementation exists."""
+
+	chosen_fac: LoopFactory[AbstractEventLoop] = DefaultLoopFactory()
+	chosen_rec: type[Receiver] | None = None
+
+	for rec in receivers:
+		fac = rec.loop_factory()
+		if fac.is_replaceable:
+			continue
+
+		if chosen_fac.is_replaceable:
+			chosen_fac = fac
+		elif type(fac) is not type(chosen_fac):
+			raise IncompatibleReceiverError(rec, not_none(chosen_rec))
+
+		chosen_rec = rec
+
+	return chosen_fac

src/mpd_now_playable/tools/types.py

@@ -31,6 +31,12 @@ AnyExceptList = (
 U = TypeVar("U")
 
 
+def not_none(value: U | None) -> U:
+	if value is None:
+		raise ValueError("None should not be possible here.")
+	return value
+
+
 def convert_if_exists(value: str | None, converter: Callable[[str], U]) -> U | None:
 	if value is None:
 		return None