<?php
/**
 * Class to increase an ID
 */

class IdIncreaser {

	private $chars = "0123456789abcdefghijklmnopqrstuvwxyz";
	private $c = NULL;

	function __construct($current, $alphabet = "") {
		if (strlen($alphabet) > 0) {
			$this->chars = $alphabet;
		}
		$this->c = new OneChar($current, $this->chars);
	}
	
	function increase() {
		$this->c->increase();
	}
	
	function build() {
		return $this->c->build();
	}

}

class OneChar {

	private $chars;
	private $otherChar = NULL;
	private $pos = 0;

	function __construct($s, $ch) {
		$this->chars = $ch;
		$current = substr($s, -1, 1);
		$this->pos = strpos($this->chars, $current);
		$s = substr($s, 0, strlen($s)-1);
		if (strlen($s) > 0) {
			$this->otherChar = new OneChar($s, $ch);
		}
	}
	
	function increase() {
		$this->pos = $this->pos + 1;
		if ($this->pos >= strlen($this->chars)) {
			$this->pos = 0;
			if ($this->otherChar != NULL) {
				$this->otherChar->increase();
			} else {
				$this->otherChar = new OneChar($this->chars[0], $this->chars);
			}
		}
	}
	
	function build() {
		if ($this->otherChar != NULL) {
			return $this->otherChar->build() . $this->chars[$this->pos];
		}
		return $this->chars[$this->pos];
	}

}