UrlShortener

UrlShortener.php

<?php

class UrlShortener{
	private static $base = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';//the real base should not be easy to guess
	private static $len = 5;
	private $salt = 0; //simple salt strategy - just shift the base
	public function __construct($salt = 0){
		$this->salt = $salt;
	}

	public function base(){
		$a = str_split(self::$base);
		$b = array_slice($a,0,$this->salt);
		array_splice($a,0,$this->salt);
		return array_merge($a,$b);
	}

	public function encode($num) {
		$ar = $this->base();
		$r = [];
		$size = count($ar);
		while($num > 0){
			$r[] = $ar[(int)($num % $size) ];
			$num = (int) ($num / $size);
		}
		return str_pad(implode('',array_reverse($r)),self::$len,$ar[0],STR_PAD_LEFT);
	}

	public function decode($str) {
		$basearr = $this->base();
		$baselen = count($basearr);
		$ar = str_split($str);
		$size = count($ar);
		$r = 0;
		for($i = 0;$i<$size;$i++){
			$r = $r*$baselen + array_search($ar[$i],$basearr);
		}
		return $r;
    }
}