fun lastCarpetId(callback: (string) -> Unit) {
val db: FirebaseFirestore = FirebaseFirestore.getInstance()
db.collection("carpets")
.orderBy("carpetid")
.limit(1)
.get()
.addOnCompleteListener {
if (it.isSuccessful) {
for (document in it.result!!) {
callback(document.data.getValue("carpetid"))
}
}
}
}