VK_Url.php

<?php

class VK_Url {
	private static $encoding = 'utf-8';
	private static $vkStr = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMN0PQRSTUVWXYZO123456789+/=';

	public static function decode($url) {
		if (strpos($url, 'audio_api_unavailable') !== false) {
			if (preg_match('/\?extra\=(.*)#(.*)/', $url, $urlArray)) {
				$extra = self::vk_o($urlArray['1']);
				$opsArray = array_reverse(explode(chr(9), self::vk_o($urlArray['2'])), true);
				foreach ($opsArray as $value) {
					$argsArray = explode(chr(11), $value);
					$op_ind = array_shift($argsArray);
					switch ($op_ind) {
						case 'v':
							$extra = self::vk_v($extra);
							break;

						case 'r':
							$extra = self::vk_r($extra, $argsArray['0']);
							break;

						case 'x':
							$extra = self::vk_x($extra, $argsArray['0']);
							break;

						case 's':
							$extra = self::vk_s($extra, $argsArray['0']);
							break;
					}
				}
				return $extra;
			}
		}
		return $url;
	}

	private static function vk_o($string) {
		$stringLen = mb_strlen($string, self::$encoding);
		$result = '';
		for ($s = 0, $index2 = 0; $s < $stringLen; $s++) {
			$sym_index = mb_strpos(self::$vkStr, $string[$s], 0, self::$encoding);
			if ($sym_index !== false) {
				$i = (($index2 % 4) !== 0) ? (($i << 6) + $sym_index) : $sym_index;
				if (($index2 % 4) != 0) {
					$index2++;
					$shift = -2 * $index2 & 6;
					$result .= chr(0xFF & ($i >> $shift));
				} else {
					$index2++;
				}
			}
		}
		return $result;
	}

	private static function vk_s($str, $start) {
		$len = strlen($str);
		if ($len > 0){
			$cur = abs($start);
			$shuffle_pos = [];
			for ($i = $len - 1; $i >= 0; $i--){
				$cur += $i;
				$shuffle_pos[$i] = $cur % $len;
			}
			for ($i = 1; $i < $len; $i++) {
				$offset = $shuffle_pos[$len - $i - 1];
				$prev = $str[$i];
				$str[$i] = $str[$offset];
				$str[$offset] = $prev;
			}
		}
		return $str;
	}

	private static function vk_v($str) {
		return strrev($str);
	}

	private static function vk_r($str, $i) {
		$vk_str2 = self::$vkStr.self::$vkStr;
		$vk_str2_len = strlen($vk_str2);
		$len = strlen($str);
		$result = '';
		for ($s = 0; $s < $len; $s++) {
			$index = strpos($vk_str2, $str[$s]);
			if ($index !== false) {
				$offset = ($index - $i);
				if ($offset < 0) {
					$offset += $vk_str2_len;
				}
				$result .= $vk_str2[$offset];
			} else {
				$result .= $str[$s];
			}
		}
		return $result;
	}

	private static function vk_x($str, $i) {
		$xor_val = ord($i['0']);
		$str_len = strlen($str);
		$result = '';
		for ($i = 0; $i < $str_len; $i++) {
			$result .= chr(ord($str[$i]) ^ $xor_val);
		}
		return $result;
	}
}