nextID.php

function nextID($id) {
		$avail_chars = $this->config->item('link_id_chars'); //a string, no dupe chars plz.
		if($id === '') {
			return $avail_chars[0];
		} else if($id[strlen($id)-1] === $avail_chars[strlen($avail_chars)-1]) {
			return $this->nextID(substr($id, 0, -1)).$avail_chars[0];
		} else {
			return substr($id, 0, -1).$avail_chars[strrpos($avail_chars,$id[strlen($id)-1])+1];
		}
	}