class Requests_IPv6 {
	/**
	 * Uncompresses an IPv6 address
	 *
	 * RFC 4291 allows you to compress consecutive zero pieces in an address to
	 * '::'. This method expects a valid IPv6 address and expands the '::' to
	 * the required number of zero pieces.
	 *
	 * Example:  FF01::101   ->  FF01:0:0:0:0:0:0:101
	 *           ::1         ->  0:0:0:0:0:0:0:1
	 *
	 * @author Alexander Merz <alexander.merz@web.de>
	 * @author elfrink at introweb dot nl
	 * @author Josh Peck <jmp at joshpeck dot org>
	 * @copyright 2003-2005 The PHP Group
	 * @license http://www.opensource.org/licenses/bsd-license.php
	 * @param string $ip An IPv6 address
	 * @return string The uncompressed IPv6 address
	 */
	public static function uncompress($ip) {
		if (substr_count($ip, '::') !== 1) {
			return $ip;
		}

		list($ip1, $ip2) = explode('::', $ip);
		$c1 = ($ip1 === '') ? -1 : substr_count($ip1, ':');
		$c2 = ($ip2 === '') ? -1 : substr_count($ip2, ':');

		if (strpos($ip2, '.') !== false) {
			$c2++;
		}
		// ::
		if ($c1 === -1 && $c2 === -1) {
			$ip = '0:0:0:0:0:0:0:0';
		}
		// ::xxx
		else if ($c1 === -1) {
			$fill = str_repeat('0:', 7 - $c2);
			$ip = str_replace('::', $fill, $ip);
		}
		// xxx::
		else if ($c2 === -1) {
			$fill = str_repeat(':0', 7 - $c1);
			$ip = str_replace('::', $fill, $ip);
		}
		// xxx::xxx
		else {
			$fill = ':' . str_repeat('0:', 6 - $c2 - $c1);
			$ip = str_replace('::', $fill, $ip);
		}
		return $ip;
	}

	/**
	 * Compresses an IPv6 address
	 *
	 * RFC 4291 allows you to compress consecutive zero pieces in an address to
	 * '::'. This method expects a valid IPv6 address and compresses consecutive
	 * zero pieces to '::'.
	 *
	 * Example:  FF01:0:0:0:0:0:0:101   ->  FF01::101
	 *           0:0:0:0:0:0:0:1        ->  ::1
	 *
	 * @see uncompress()
	 * @param string $ip An IPv6 address
	 * @return string The compressed IPv6 address
	 */
	public static function compress($ip) {
		// Prepare the IP to be compressed
		$ip = self::uncompress($ip);
		$ip_parts = self::split_v6_v4($ip);

		// Replace all leading zeros
		$ip_parts[0] = preg_replace('/(^|:)0+([0-9])/', '\1\2', $ip_parts[0]);

		// Find bunches of zeros
		if (preg_match_all('/(?:^|:)(?:0(?::|$))+/', $ip_parts[0], $matches, PREG_OFFSET_CAPTURE)) {
			$max = 0;
			$pos = null;
			foreach ($matches[0] as $match) {
				if (strlen($match[0]) > $max) {
					$max = strlen($match[0]);
					$pos = $match[1];
				}
			}

			$ip_parts[0] = substr_replace($ip_parts[0], '::', $pos, $max);
		}

		if ($ip_parts[1] !== '') {
			return implode(':', $ip_parts);
		}
		else {
			return $ip_parts[0];
		}
	}

	/**
	 * Splits an IPv6 address into the IPv6 and IPv4 representation parts
	 *
	 * RFC 4291 allows you to represent the last two parts of an IPv6 address
	 * using the standard IPv4 representation
	 *
	 * Example:  0:0:0:0:0:0:13.1.68.3
	 *           0:0:0:0:0:FFFF:129.144.52.38
	 *
	 * @param string $ip An IPv6 address
	 * @return string[] [0] contains the IPv6 represented part, and [1] the IPv4 represented part
	 */
	protected static function split_v6_v4($ip) {
		if (strpos($ip, '.') !== false) {
			$pos = strrpos($ip, ':');
			$ipv6_part = substr($ip, 0, $pos);
			$ipv4_part = substr($ip, $pos + 1);
			return array($ipv6_part, $ipv4_part);
		}
		else {
			return array($ip, '');
		}
	}

	/**
	 * Checks an IPv6 address
	 *
	 * Checks if the given IP is a valid IPv6 address
	 *
	 * @param string $ip An IPv6 address
	 * @return bool true if $ip is a valid IPv6 address
	 */
	public static function check_ipv6($ip) {
		$ip = self::uncompress($ip);
		list($ipv6, $ipv4) = self::split_v6_v4($ip);
		$ipv6 = explode(':', $ipv6);
		$ipv4 = explode('.', $ipv4);
		if (count($ipv6) === 8 && count($ipv4) === 1 || count($ipv6) === 6 && count($ipv4) === 4) {
			foreach ($ipv6 as $ipv6_part) {
				// The section can't be empty
				if ($ipv6_part === '') {
					return false;
				}

				// Nor can it be over four characters
				if (strlen($ipv6_part) > 4) {
					return false;
				}

				// Remove leading zeros (this is safe because of the above)
				$ipv6_part = ltrim($ipv6_part, '0');
				if ($ipv6_part === '') {
					$ipv6_part = '0';
				}

				// Check the value is valid
				$value = hexdec($ipv6_part);
				if (dechex($value) !== strtolower($ipv6_part) || $value < 0 || $value > 0xFFFF) {
					return false;
				}
			}
			if (count($ipv4) === 4) {
				foreach ($ipv4 as $ipv4_part) {
					$value = (int) $ipv4_part;
					if ((string) $value !== $ipv4_part || $value < 0 || $value > 0xFF) {
						return false;
					}
				}
			}
			return true;
		}
		else {
			return false;
		}
	}
}