fix starting queue from nth occurrence of a track in playlist starts queue from 1st occurrence, where n > 1

[HeroBrine1st]

Changes

TracksSliverList searches first instance of track in prepared queue, even if user taps later instances, then starts queue there. This means that for a playlist of:

1. Track A
2. Track B
3. Track C
4. Track B
5. Track D

Tapping on item 4 starts queue from item 2, which is not correct.

This PR fixes that by assuming duplicates are only possible in this branch since the other branch is guarded against playlists:

finamp/lib/components/AlbumScreen/album_screen_content.dart

Lines 219 to 227 in e8302a2

	else if (!isLoading)
	TracksSliverList(
	childrenForList: displayChildren,
	childrenForQueue: queueChildren,
	parent: widget.parent,
	onRemoveFromList: onDelete,
	adaptiveAdditionalInfoSortBy: (parentIsPlaylist) ? sortSetting.sortBy : null,
	forceAlbumArtists: (parentIsPlaylist && sortSetting.sortBy == SortBy.albumArtist),
	)

Then, due to the fact queueChildren is a sparse sublist of displayChildren, it's possible to count duplicates in displayChildren preceding tapped item; then, assuming tracks with the same id are either all playable or not (i.e. for all tracks it is either playable or not, see law of excluded middle :P), skipping the same number of duplicates in queueChildren means taking a track at exactly the same position. When it's zero (no duplicates, e.g. an album), it's the same behavior, and when current track is not playable it falls back to -1 as a workaround to the fact it is calculated eagerly even for unplayable tracks.

There is another approach: pass concatenated list of previous queueForLists (which would still be displayChildren for the branch mentioned above and accumulated list for preceding album with discs branch) to be used to calculate dupesBefore. It's only better if albums can have duplicates, too, which isn't possible in Jellyfin I hope.

The only problem with all of this elegance is the fact flutter let me down and doesn't build Finamp due to stdlib problems, and I can't update it at the moment. This was planned to be 20-minute adventure which went wrong for more than 1 hour so idk. I hope CI creates android artifact which I can test myself later.

Todo before merging

• Test it
• .where(...).length can possibly be replaced with some kind of count(...) but I didn't find any
• (Possible follow-up) reduce O(n^2) to O(n) by delaying index calculation into a lambda since it's only required on tap; quadratic complexity is not introduced by this PR

---

dart format . let me down too. What a day. It changes nothing on my system.

[HeroBrine1st]

okay my CI got new flutter successfully so I tested it on n=2. It now correctly picks second occurence of track when I pick it, and first one is unchanged. I tested multi-disc album too, no issues.