class_name SnapshotFragments
extends RefCounted

const PART_BYTES := 1000
const MAX_PARTS := 64
var sequence := -1
var expected := 0
var pieces: Dictionary[int, PackedByteArray] = {}

func accept(serial: int, index: int, count: int, bytes: PackedByteArray) -> PackedByteArray:
	if serial < sequence or count < 1 or count > MAX_PARTS or index < 0 or index >= count or bytes.is_empty() or bytes.size() > PART_BYTES:
		return PackedByteArray()
	if serial > sequence:
		sequence = serial
		expected = count
		pieces.clear()
	if count != expected: return PackedByteArray()
	pieces[index] = bytes
	if pieces.size() != count: return PackedByteArray()
	var result := PackedByteArray()
	for i in count: result.append_array(pieces[i])
	pieces.clear()
	expected = 0 # Ignore duplicate fragments of an already applied snapshot.
	return result