# Substrings of a Rope (i.e. Reverse postfix iterator on leaves)
private class ReverseRopeSubstrings
	super IndexedIterator[FlatString]

	# Visit Stack
	var iter: RopeCharIteratorPiece is noinit
	# Position in `Rope`
	var pos: Int is noinit

	# Current leaf
	var str: FlatString is noinit

	init from(root: Concat, pos: Int) do
		var r = new RopeCharIteratorPiece(root, false, true, null)
		var rnod: String = root
		var off = pos
		loop
			if rnod isa Concat then
				if off >= rnod._left.length then
					off -= rnod._left.length
					rnod = rnod._right
					r = new RopeCharIteratorPiece(rnod, false, true, r)
				else
					r.ldone = true
					rnod = rnod._left
					r = new RopeCharIteratorPiece(rnod, false, true, r)
				end
			else
				str = rnod.as(FlatString)
				r.ldone = true
				iter = r
				self.pos = pos - off
				break
			end
		end
	end

	redef fun item do return str

	redef fun index do return pos

	redef fun is_ok do return pos >= 0

	redef fun next do
		if pos < 0 then return
		var curr = iter.prev
		var currit = curr.as(not null).node
		while curr != null do
			currit = curr.node
			if not currit isa Concat then
				str = currit.as(FlatString)
				pos -= str.length
				iter = curr
				return
			end
			if not curr.rdone then
				curr.rdone = true
				curr = new RopeCharIteratorPiece(currit._right, false, false, curr)
				continue
			end
			if not curr.ldone then
				curr.ldone = true
				curr = new RopeCharIteratorPiece(currit._left, false, false, curr)
				continue
			end
			curr = curr.prev
		end
		pos = -1
	end
end