## Contain a subset of notes in a [NoteArray].
## Notes are expected to be sorted in ascending order by beat.
## The original index of a note can be found with [method id_at].
class_name NoteSubset extends NoteArray

## The array where notes in this subset come from.
var full_set: NoteArray

## The ID (index of note in full_set) of the note at [param index].
func id_at(index) -> int:
	return _ids.get(index)

## Parse the given [param notes] and return a [class NoteSubset]
## containing only notes in [param lane].
static func get_notes_in_lane(notes: NoteArray, lane: int) -> NoteSubset:
	var lane_notes: NoteSubset = NoteSubset.new()
	lane_notes.full_set = notes
	for i in range(notes.size( )):
		if notes.lane_at(i) == lane:
			lane_notes._ids.append(i)
			lane_notes.append_note_data(notes.beat_at(i), notes.type_at(i), lane)
	return lane_notes

## ====== IMPLEMENTATION ====== #
var _ids: Array[int] = []