Initialise FadeCurve in a thread

Stops a UI delay of half a second or so when marking a track 'next'

app/classes.py

@@ -2,32 +2,34 @@ from dataclasses import dataclass
 from datetime import datetime, timedelta
 from typing import Optional
 
-from PyQt6.QtCore import pyqtSignal, QObject
+from PyQt6.QtCore import pyqtSignal, QObject, QThread
 import numpy as np
 import pyqtgraph as pg  # type: ignore
 
 from config import Config
-from dbconfig import scoped_session
-from models import PlaylistRows
+from dbconfig import scoped_session, Session
+from models import PlaylistRows, Tracks
 import helpers
 
 
 class FadeCurve:
     GraphWidget = None
 
-    def __init__(self, track):
+    def __init__(
+        self, track_path: str, track_fade_at: int, track_silence_at: int
+    ) -> None:
         """
         Set up fade graph array
         """
 
-        audio = helpers.get_audio_segment(track.path)
+        audio = helpers.get_audio_segment(track_path)
         if not audio:
             return None
 
         # Start point of curve is Config.FADE_CURVE_MS_BEFORE_FADE
         # milliseconds before fade starts to silence
-        self.start_ms = max(0, track.fade_at - Config.FADE_CURVE_MS_BEFORE_FADE - 1)
-        self.end_ms = track.silence_at
+        self.start_ms = max(0, track_fade_at - Config.FADE_CURVE_MS_BEFORE_FADE - 1)
+        self.end_ms = track_silence_at
         self.audio_segment = audio[self.start_ms : self.end_ms]
         self.graph_array = np.array(self.audio_segment.get_array_of_samples())
 
@@ -106,7 +108,7 @@ class PlaylistTrack:
         self.duration: Optional[int] = None
         self.end_time: Optional[datetime] = None
         self.fade_at: Optional[int] = None
-        self.fade_curve: Optional[FadeCurve] = None
+        self.fade_graph: Optional[FadeCurve] = None
         self.fade_length: Optional[int] = None
         self.path: Optional[str] = None
         self.playlist_id: Optional[int] = None
@@ -139,7 +141,6 @@ class PlaylistTrack:
         self.duration = track.duration
         self.end_time = None
         self.fade_at = track.fade_at
-        self.fade_graph = FadeCurve(track)  # TODO: speed this line up
         self.path = track.path
         self.playlist_id = plr.playlist_id
         self.plr_id = plr.id
@@ -153,6 +154,22 @@ class PlaylistTrack:
         if track.silence_at and track.fade_at:
             self.fade_length = track.silence_at - track.fade_at
 
+        # Initialise and add FadeCurve in a thread as it's slow
+        # Import in separate thread
+        self.fadecurve_thread = QThread()
+        self.worker = AddFadeCurve(
+            self,
+            track_path=track.path,
+            track_fade_at=track.fade_at,
+            track_silence_at=track.silence_at,
+        )
+        self.worker.moveToThread(self.fadecurve_thread)
+        self.fadecurve_thread.started.connect(self.worker.run)
+        self.worker.finished.connect(self.fadecurve_thread.quit)
+        self.worker.finished.connect(self.worker.deleteLater)
+        self.fadecurve_thread.finished.connect(self.fadecurve_thread.deleteLater)
+        self.fadecurve_thread.start()
+
     def start(self) -> None:
         """
         Called when track starts playing
@@ -163,6 +180,38 @@ class PlaylistTrack:
             self.end_time = self.start_time + timedelta(milliseconds=self.duration)
 
 
+class AddFadeCurve(QObject):
+    """
+    Initialising a fade curve introduces a noticeable delay so carry out in
+    a thread.
+    """
+
+    finished = pyqtSignal()
+
+    def __init__(
+        self,
+        playlist_track: PlaylistTrack,
+        track_path: str,
+        track_fade_at: int,
+        track_silence_at: int,
+    ):
+        super().__init__()
+        self.playlist_track = playlist_track
+        self.track_path = track_path
+        self.track_fade_at = track_fade_at
+        self.track_silence_at = track_silence_at
+
+    def run(self):
+        """
+        Create fade curve and add to PlaylistTrack object
+        """
+
+        self.playlist_track.fade_graph = FadeCurve(
+            self.track_path, self.track_fade_at, self.track_silence_at
+        )
+        self.finished.emit()
+
+
 @helpers.singleton
 class CurrentTrack(PlaylistTrack):
     pass