Make row number a playlist-only concept

Solves problem of rows being moved in playlist and musicmuster not
knowing which row the current/next track is (but it doesn't need to
know; it only needs to know the PlaylistRows id).

app/musicmuster.py

@@ -120,6 +120,10 @@ class PlaylistTrack:
     def __init__(self) -> None:
         """
         Only initialises data structure. Call set_plr to populate.
+
+        Do NOT store row_number here - that changes if tracks are reordered
+        in playlist (add, remove, drag/drop) and we shouldn't care about row
+        number: that's the playlist's problem.
         """
 
         self.artist = None
@@ -131,7 +135,6 @@ class PlaylistTrack:
         self.playlist_id = None
         self.playlist_tab = None
         self.plr_id = None
-        self.row_number = None
         self.silence_at = None
         self.start_gap = None
         self.start_time = None
@@ -163,7 +166,6 @@ class PlaylistTrack:
         self.path = track.path
         self.playlist_id = plr.playlist_id
         self.plr_id = plr.id
-        self.row_number = plr.row_number
         self.silence_at = track.silence_at
         self.start_gap = track.start_gap
         self.start_time = None

app/playlists.py

@@ -720,6 +720,11 @@ class PlaylistTab(QTableWidget):
 
         current_row = self._get_current_track_row_number()
         if not current_row:
+            send_mail(Config.ERRORS_TO,
+                      Config.ERRORS_FROM,
+                      "MusicMuster unexpected failure",
+                      stackprinter.format()
+                      )
             return
 
         search_from = current_row + 1
@@ -749,6 +754,11 @@ class PlaylistTab(QTableWidget):
         # Add the rows
         playlist = session.get(Playlists, playlist_id)
         if not playlist:
+            send_mail(Config.ERRORS_TO,
+                      Config.ERRORS_FROM,
+                      "MusicMuster unexpected failure",
+                      stackprinter.format()
+                      )
             return
 
         for plr in playlist.rows:
@@ -963,8 +973,8 @@ class PlaylistTab(QTableWidget):
         - Show unplayed tracks in bold
         """
 
-        current_row: Optional[int] = self._get_current_track_row_number()
+        current_row = self._get_current_track_row_number()
-        next_row: Optional[int] = self._get_next_track_row_number()
+        next_row = self._get_next_track_row_number()
         played = [
             p.row_number for p in PlaylistRows.get_played_rows(
                 session, self.playlist_id)
@@ -1313,23 +1323,13 @@ class PlaylistTab(QTableWidget):
         """Return current track row or None"""
 
         current_track = self.musicmuster.current_track
-        if not current_track.track_id:
+        return self._plrid_to_row_number(current_track.plr_id)
-            return None
-        if current_track.playlist_tab == self:
-            return current_track.row_number
-        else:
-            return None
 
     def _get_next_track_row_number(self) -> Optional[int]:
         """Return next track row or None"""
 
         next_track = self.musicmuster.next_track
-        if not next_track.track_id:
+        return self._plrid_to_row_number(next_track.plr_id)
-            return None
-        if next_track.playlist_tab == self:
-            return next_track.row_number
-        else:
-            return None
 
     @staticmethod
     def _get_note_text_time(text: str) -> Optional[datetime]:
@@ -1571,6 +1571,17 @@ class PlaylistTab(QTableWidget):
 
             open_in_audacity(track.path)
 
+    def _plrid_to_row_number(self, plrid: int) -> Optional[int]:
+        """
+        Return row number of passed plrid, or None if not found
+        """
+
+        for row_number in range(self.rowCount()):
+            if self._get_playlistrow_id(row_number) == plrid:
+                return row_number
+
+        return None
+
     def _remove_track(self, row: int) -> None:
         """Remove track from row, making it a section header"""