<?php

namespace Badcow\DNS;

use Badcow\DNS\Rdata\CNAME;
use Badcow\DNS\Rdata\NS;
use Badcow\DNS\Rdata\SOA;

class Validator
{
	const ZONE_OKAY = 0;
	const ZONE_NO_SOA = 1;
	const ZONE_TOO_MANY_SOA = 2;
	const ZONE_NO_NS = 4;
	const ZONE_NO_CLASS = 8;
	const ZONE_TOO_MANY_CLASSES = 16;

	/**
	 * Validate the string as a valid hostname in accordance with RFC 952 {@link https://tools.ietf.org/html/rfc952}
	 * and RFC 1123 {@link https://tools.ietf.org/html/rfc1123}.
	 *
	 * @param string $name
	 *
	 * @return bool
	 */
	public static function hostName(string $name): bool
	{
		return self::fullyQualifiedDomainName(rtrim($name, '.').'.');
	}


	/**
	 * Validate the string is a Fully Qualified Domain Name.
	 *
	 * @param string $name
	 *
	 * @return bool
	 */
	public static function fullyQualifiedDomainName(string $name): bool
	{
		if ('.' === $name) {
		    return true;
		}

		return strlen($name) < 254 &&
		    (1 === preg_match('/^(?:(?!-)[a-z0-9\-]{1,63}(?<!-)\.){1,127}$/i', $name));
	}


	/**
	 * Validate the name for a Resource Record. This is distinct from validating a hostname in that this function
	 * will permit '@' and wildcards as well as underscores used in SRV records.
	 *
	 * @param string $name
	 *
	 * @return bool
	 */
	public static function resourceRecordName(string $name): bool
	{
		return strlen($name) < 254 &&
		    (1 === preg_match('/(?:^(?:\*\.)?((?!-)[a-z0-9_\-]{1,63}(?<!-)\.?){1,127}$)|^@$|^\*$/i', $name));
	}


	/**
	 * Validates an IPv4 Address.
	 *
	 * @static
	 *
	 * @param string $address
	 *
	 * @return bool
	 */
	public static function ipv4(string $address): bool
	{
		return (bool) filter_var($address, FILTER_VALIDATE_IP, [
		    'flags' => FILTER_FLAG_IPV4,
		]);
	}


	/**
	 * Validates an IPv6 Address.
	 *
	 * @static
	 *
	 * @param string $address
	 *
	 * @return bool
	 */
	public static function ipv6(string $address): bool
	{
		return (bool) filter_var($address, FILTER_VALIDATE_IP, [
		    'flags' => FILTER_FLAG_IPV6,
		]);
	}


	/**
	 * Validates an IPv4 or IPv6 address.
	 *
	 * @static
	 *
	 * @param string $address
	 *
	 * @return bool
	 */
	public static function ipAddress(string $address): bool
	{
		return (bool) filter_var($address, FILTER_VALIDATE_IP);
	}


	/**
	 * Validates that the zone meets
	 * RFC-1035 especially that:
	 *   1) 5.2.1 All RRs in the file should be of the same class.
	 *   2) 5.2.2 Exactly one SOA RR should be present at the top of the zone.
	 *   3) There is at least one NS record.
	 *
	 * Return values are:
	 *   - ZONE_NO_SOA
	 *   - ZONE_TOO_MANY_SOA
	 *   - ZONE_NO_NS
	 *   - ZONE_NO_CLASS
	 *   - ZONE_TOO_MANY_CLASSES
	 *   - ZONE_OKAY
	 *
	 * You SHOULD compare these return values to the defined constants of this
	 * class rather than against integers directly.
	 *
	 * @param Zone $zone
	 *
	 * @return int
	 */
	public static function zone(Zone $zone): int
	{
		$n_soa = self::countResourceRecords($zone, SOA::TYPE);
		$n_ns = self::countResourceRecords($zone, NS::TYPE);
		$n_class = self::countClasses($zone);

		$totalError = 0;

		$incrementError = function (bool $errorCondition, int $errorOrdinal) use (&$totalError): void {
		    $totalError += $errorCondition ? $errorOrdinal : 0;
		};

		$incrementError($n_soa < 1, self::ZONE_NO_SOA);
		$incrementError($n_soa > 1, self::ZONE_TOO_MANY_SOA);
		$incrementError($n_ns < 1, self::ZONE_NO_NS);
		$incrementError($n_class < 1, self::ZONE_NO_CLASS);
		$incrementError($n_class > 1, self::ZONE_TOO_MANY_CLASSES);

		return $totalError;
	}


	/**
	 * Counts the number of Resource Records of a particular type ($type) in a Zone.
	 *
	 * @param Zone   $zone
	 * @param string $type The ResourceRecord type to be counted. If NULL, then the method will return
	 *                     the number of records without RData.
	 *
	 * @return int the number of records to be counted
	 */
	public static function countResourceRecords(Zone $zone, ?string $type = null): int
	{
		$n = 0;
		foreach ($zone as $rr) {
		    $n += (int) ($type === $rr->getType());
		}

		return $n;
	}


	/**
	 * Validates a reverse IPv4 address. Ensures that all octets are in the range [0-255].
	 *
	 * @param string $address
	 *
	 * @return bool
	 */
	public static function reverseIpv4(string $address): bool
	{
		$pattern = '/^((?:[0-9]+\.){1,4})in\-addr\.arpa\.$/i';

		if (1 !== preg_match($pattern, $address, $matches)) {
		    return false;
		}

		$octets = explode('.', $matches[1]);
		array_pop($octets); //Remove the last decimal from the array

		foreach ($octets as $octet) {
		    if ((int) $octet > 255) {
		        return false;
		    }
		}

		return true;
	}


	/**
	 * Validates a reverse IPv6 address.
	 *
	 * @param string $address
	 *
	 * @return bool
	 */
	public static function reverseIpv6(string $address): bool
	{
		$pattern = '/^(?:[0-9a-f]\.){1,32}ip6\.arpa\.$/i';

		return 1 === preg_match($pattern, $address);
	}


	/**
	 * Determine the number of unique non-null classes in a Zone. In a valid zone this MUST be 1.
	 *
	 * @param Zone $zone
	 *
	 * @return int
	 */
	private static function countClasses(Zone $zone): int
	{
		$classes = [];

		foreach ($zone as $rr) {
		    if (null !== $rr->getClass()) {
		        $classes[$rr->getClass()] = null;
		    }
		}

		return count($classes);
	}


	/**
	 * Ensure $zone does not contain existing CNAME alias corresponding to $newRecord's name.
	 *
	 * E.g.
	 *      www IN CNAME example.com.
	 *      www IN TXT "This is a violation of DNS specifications."
	 *
	 * @see https://tools.ietf.org/html/rfc1034#section-3.6.2
	 *
	 * @param Zone           $zone
	 * @param ResourceRecord $newRecord
	 *
	 * @return bool
	 */
	public static function noAliasInZone(Zone $zone, ResourceRecord $newRecord): bool
	{
		foreach ($zone as $rr) {
		    if (CNAME::TYPE === $rr->getType()
		        && $newRecord->getName() === $rr->getName()) {
		        return false;
		    }
		}

		return true;
	}


	/**
	 * Determine if string is a base64 encoded string.
	 *
	 * @param string $string A base64 encoded string
	 *
	 * @return bool
	 */
	public static function isBase64Encoded(string $string): bool
	{
		if (1 !== preg_match('/^[a-zA-Z0-9\/\r\n+ ]*={0,2}$/', $string)) {
		    return false;
		}

		if (null === $string = preg_replace('/[^a-zA-Z0-9\/+=]/', '', $string)) {
		    return false;
		}

		if (false === $decoded = base64_decode($string, true)) {
		    return false;
		}

		return $string === base64_encode($decoded);
	}


	/**
	 * Determine if string is a base32 encoded string.
	 *
	 * @param string $string
	 *
	 * @return bool
	 */
	public static function isBase32Encoded(string $string): bool
	{
		return 1 === preg_match('/^[A-Z2-7]+=*$/', $string);
	}


	/**
	 * Determine if string is a base32hex (extended hex) encoded string.
	 *
	 * @param string $string
	 *
	 * @return bool
	 */
	public static function isBase32HexEncoded(string $string): bool
	{
		return 1 === preg_match('/^[a-zA-Z0-9]+=*$/', $string);
	}


	/**
	 * Determine if string is a base16 encoded string.
	 *
	 * @param string $string
	 *
	 * @return bool
	 */
	public static function isBase16Encoded(string $string): bool
	{
		return 1 === preg_match('/^[0-9a-f]+$/i', $string);
	}


	/**
	 * Determine if $integer is an unsigned integer less than 2^$numberOfBits.
	 *
	 * @param int $integer      The integer to test
	 * @param int $numberOfBits The upper limit that the integer can be expressed as an exponent of 2
	 *
	 * @return bool
	 */
	public static function isUnsignedInteger(int $integer, int $numberOfBits): bool
	{
		$maxBits = PHP_INT_SIZE * 8 - 1;

		if ($numberOfBits > $maxBits) {
		    throw new \RuntimeException(sprintf('Number of bits "%d" exceeds maximum binary exponent of "%d".', $numberOfBits, $maxBits));
		}

		return (0 <= $integer) && ($integer < (2 ** $numberOfBits));
	}
}
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