<?php

/**
 * webtrees: online genealogy
 * Copyright (C) 2019 webtrees development team
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
 * GNU General Public License for more details.
 * You should have received a copy of the GNU General Public License
 * along with this program. If not, see <http://www.gnu.org/licenses/>.
 */

declare(strict_types=1);

namespace Fisharebest\Webtrees\Http\Middleware;

use Fig\Http\Message\StatusCodeInterface;
use Fisharebest\Webtrees\Cache;
use Illuminate\Support\Str;
use Iodev\Whois\Loaders\CurlLoader;
use Iodev\Whois\Modules\Asn\AsnRouteInfo;
use Iodev\Whois\Whois;
use IPLib\Address\AddressInterface;
use IPLib\Factory;
use IPLib\Range\RangeInterface;
use Psr\Http\Message\ResponseInterface;
use Psr\Http\Message\ServerRequestInterface;
use Psr\Http\Server\MiddlewareInterface;
use Psr\Http\Server\RequestHandlerInterface;
use Throwable;

use function app;
use function array_map;
use function assert;
use function gethostbyaddr;
use function gethostbyname;
use function in_array;
use function response;

/**
 * Middleware to block bad robots before they waste our valuable CPU cycles.
 */
class BadBotBlocker implements MiddlewareInterface
{
    // Cache whois requests.  Try to avoid all caches expiring at the same time.
    private const WHOIS_TTL_MIN = 28 * 86400;
    private const WHOIS_TTL_MAX = 35 * 86400;
    private const WHOIS_TIMEOUT = 5;

    // Bad robots - SEO optimisers, advertisers, etc
    private const BAD_ROBOTS = [
        'admantx',
        'AhrefsBot',
        'DotBot',
        'Grapeshot',
        'ia_archiver',
        'MJ12bot',
        'proximic',
        'SemrushBot',
        'XoviBot',
    ];

    /**
     * Some search engines provide reverse DNS to verify the IP address.
     *
     * @see https://support.google.com/webmasters/answer/80553?hl=en
     * @see https://www.bing.com/webmaster/help/which-crawlers-does-bing-use-8c184ec0
     * @see https://www.bing.com/webmaster/help/how-to-verify-bingbot-3905dc26
     * @see https://yandex.com/support/webmaster/robot-workings/check-yandex-robots.html
     * @see https://help.baidu.com/question?prod_id=99&class=0&id=3001
     */
    private const ROBOT_DNS = [
        'Baidu'       => ['.baidu.com', '.baidu.jp'],
        'bingbot'     => ['.search.msn.com'],
        'BingPreview' => ['.search.msn.com'],
        'Google'      => ['.google.com', '.googlebot.com'],
        'msnbot'      => ['.search.msn.com'],
        'Qwantify'    => ['.search.qwant.com'],
        'Sogou'       => ['.crawl.sogou.com'],
        'Yahoo'       => ['.crawl.yahoo.net'],
        'Yandex'      => ['.yandex.ru', '.yandex.net', '.yandex.com'],
    ];

    /**
     * Some search engines operate from designated IP addresses.
     *
     * @see https://help.duckduckgo.com/duckduckgo-help-pages/results/duckduckbot
     */
    private const ROBOT_IPS = [
        'Ask Jeeves'  => [
            '65.214.45.143',
            '65.214.45.148',
            '66.235.124.192',
            '66.235.124.7',
            '66.235.124.101',
            '66.235.124.193',
            '66.235.124.73',
            '66.235.124.196',
            '66.235.124.74',
            '63.123.238.8',
            '202.143.148.61',
        ],
        'DuckDuckBot' => [
            '23.21.227.69',
            '50.16.241.113',
            '50.16.241.114',
            '50.16.241.117',
            '50.16.247.234',
            '52.204.97.54',
            '52.5.190.19',
            '54.197.234.188',
            '54.208.100.253',
            '54.208.102.37',
            '107.21.1.8',
        ],
    ];

    /**
     * Some search engines operate from within a designated autonomous system.
     *
     * @see https://developers.facebook.com/docs/sharing/webmasters/crawler
     */
    private const ROBOT_ASN = [
        'facebook' => 'AS32934',
        'twitter'  => 'AS13414',
    ];

    /**
     * These ASNs belong to server farms.
     */
    private const BLOCK_ASN = [
        'hetzner'   => 'AS24920',
        'hostdime'  => 'AS33182',
        'linode'    => 'AS63949',
        'ovh'       => 'AS16276',
        'rackspace' => 'AS15395',
    ];

    /**
     * @param ServerRequestInterface  $request
     * @param RequestHandlerInterface $handler
     *
     * @return ResponseInterface
     */
    public function process(ServerRequestInterface $request, RequestHandlerInterface $handler): ResponseInterface
    {
        $ua      = $request->getServerParams()['HTTP_USER_AGENT'] ?? '';
        $ip      = $request->getAttribute('client-ip');
        $address = Factory::addressFromString($ip);
        assert($address instanceof AddressInterface);

        if (Str::contains($ua, self::BAD_ROBOTS)) {
            return $this->response();
        }

        foreach (self::ROBOT_DNS as $robot => $valid_domains) {
            if (Str::contains($ua, $robot) && !$this->checkReverseDNS($ip, $valid_domains)) {
                return $this->response();
            }
        }

        foreach (self::ROBOT_IPS as $robot => $valid_ips) {
            if (Str::contains($ua, $robot) && !in_array($ip, $valid_ips, true)) {
                return $this->response();
            }
        }

        foreach (self::ROBOT_ASN as $robot => $asn) {
            if (Str::contains($ua, $robot)) {
                foreach ($this->fetchIpRangesForAsn($asn) as $range) {
                    if ($range->contains($address)) {
                        continue 2;
                    }
                }

                return $this->response();
            }
        }

        // This is potentially controversial, and whois lookups may be slow.
        //foreach (self::BLOCK_ASN as $host => $asn) {
        //    foreach ($this->fetchIpRangesForAsn($asn) as $range) {
        //        if ($range->contains($address)) {
        //            return $this->response();
        //        }
        //    }
        //}

        return $handler->handle($request);
    }

    /**
     * Check that an IP address belongs to a robot operator using a forward/reverse DNS lookup.
     *
     * @param string        $ip
     * @param array<string> $valid_domains
     *
     * @return bool
     */
    private function checkReverseDNS(string $ip, array $valid_domains): bool
    {
        $host = gethostbyaddr($ip);

        if ($host === false || !Str::endsWith($host, $valid_domains)) {
            return false;
        }

        return $ip === gethostbyname($host);
    }

    /**
     * Perform a whois search for an ASN.
     *
     * @param string $asn - The autonomous system number to query
     *
     * @return array<RangeInterface>
     */
    private function fetchIpRangesForAsn(string $asn): array
    {
        $cache = app('cache.files');
        assert($cache instanceof Cache);

        return $cache->remember('whois-asn-' . $asn, static function () use ($asn): array {
            try {
                $loader = new CurlLoader(self::WHOIS_TIMEOUT);
                $whois  = new Whois($loader);
                $info   = $whois->loadAsnInfo($asn);
                $routes = $info->getRoutes();
                $ranges = array_map(static function (AsnRouteInfo $route_info): ?RangeInterface {
                    return Factory::rangeFromString($route_info->getRoute() ?: $route_info->getRoute6());
                }, $routes);

                return array_filter($ranges);
            } catch (Throwable $ex) {
                return [];
            }
        }, random_int(self::WHOIS_TTL_MIN, self::WHOIS_TTL_MAX));
    }

    /**
     * @return ResponseInterface
     */
    private function response(): ResponseInterface
    {
        return response('Not acceptable', StatusCodeInterface::STATUS_NOT_ACCEPTABLE);
    }
}