Support persistent track IDs (64-bit ints)

src/mpd_now_playable/cli.py

@@ -3,7 +3,7 @@ from os import environ
 
 from corefoundationasyncio import CoreFoundationEventLoop
 
-from .cocoa import CocoaNowPlaying
+from .cocoa.now_playing import CocoaNowPlaying
 from .mpd.listener import MpdStateListener
 
 

src/mpd_now_playable/cocoa/now_playing.py

@@ -12,6 +12,7 @@ from MediaPlayer import (
 	MPMediaItemPropertyComposer,
 	MPMediaItemPropertyDiscNumber,
 	MPMediaItemPropertyGenre,
+	MPMediaItemPropertyPersistentID,
 	MPMediaItemPropertyPlaybackDuration,
 	MPMediaItemPropertyTitle,
 	MPMusicPlaybackState,
@@ -32,9 +33,10 @@ from MediaPlayer import (
 	MPRemoteCommandHandlerStatus,
 )
 
-from .async_tools import run_background_task
-from .player import Player
-from .song import PlaybackState, Song
+from ..async_tools import run_background_task
+from ..player import Player
+from ..song import PlaybackState, Song
+from .persistent_id import song_to_persistent_id
 
 
 def logo_to_ns_image() -> NSImage:
@@ -81,6 +83,7 @@ def song_to_media_item(song: Song) -> NSMutableDictionary:
 	nowplaying_info[MPNowPlayingInfoPropertyExternalContentIdentifier] = song.file
 	nowplaying_info[MPNowPlayingInfoPropertyPlaybackQueueCount] = song.queue_length
 	nowplaying_info[MPNowPlayingInfoPropertyPlaybackQueueIndex] = song.queue_index
+	nowplaying_info[MPMediaItemPropertyPersistentID] = song_to_persistent_id(song)
 
 	nowplaying_info[MPMediaItemPropertyTitle] = song.title
 	nowplaying_info[MPMediaItemPropertyArtist] = song.artist

src/mpd_now_playable/cocoa/persistent_id.py

@@ -0,0 +1,39 @@
+from hashlib import blake2b
+from pathlib import Path
+from typing import Final
+from uuid import UUID
+
+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."
+TRACKID_HASH_PERSON: Final = HASH_PERSON_PREFIX + b"mb_tid"
+FILE_HASH_PERSON: Final = HASH_PERSON_PREFIX + b"f"
+
+PERSISTENT_ID_BITS: Final = 64
+PERSISTENT_ID_BYTES: Final = PERSISTENT_ID_BITS // 8
+
+
+def digest_trackid(trackid: UUID) -> bytes:
+	return blake2b(
+		trackid.bytes, digest_size=PERSISTENT_ID_BYTES, person=TRACKID_HASH_PERSON
+	).digest()
+
+
+def digest_file_uri(file: Path) -> bytes:
+	return blake2b(
+		bytes(file), digest_size=PERSISTENT_ID_BYTES, person=FILE_HASH_PERSON
+	).digest()
+
+
+# The MPMediaItemPropertyPersistentID is only 64 bits, while a UUID is 128
+# bits and not all tracks will even have their MusicBrainz track ID included.
+# To work around this, we compute a BLAKE2 hash from the UUID, or failing
+# that from the file URI. BLAKE2 can be customised to different digest sizes,
+# making it perfect for this problem.
+def song_to_persistent_id(song: Song) -> int:
+	if song.musicbrainz_trackid:
+		hashed_id = digest_trackid(song.musicbrainz_trackid)
+	else:
+		hashed_id = digest_file_uri(song.file)
+	return int.from_bytes(hashed_id)