Support persistent track IDs (64-bit ints)

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)