webmentions/src/EndpointParser.php

<?php declare(strict_types=1);

namespace Lewisdale\Webmentions;

use Symfony\Contracts\HttpClient\ResponseInterface;
use Symfony\Component\DomCrawler\Crawler;
use League\Uri\Uri;
use League\Uri\UriInfo;
use League\Uri\UriResolver;

class EndpointParser {
    public static function parse(ResponseInterface $response) : string | null
    {
        $endpoint = self::parseHeaders($response) ?? self::parseBody($response);
        return self::absoluteURL($response, $endpoint);
    }

    private static function parseHeaders(ResponseInterface $response) : string | null {
        $headers = $response->getHeaders();

        if (isset($headers["link"])) {
            foreach($headers["link"] as $link) {
                if (preg_match('/rel=("?)webmention("?)/', $link)) {
                    $matches = [];
                    preg_match('/\<(..*?)\>/', $link, $matches);

                    if (count($matches) > 1) {
                        return $matches[1];
                    }
                }
            }   
        }

        return null;
    }

    private static function absoluteURL(ResponseInterface $response, ?string $endpoint) : string | null {
        if (!$endpoint) {
            return null;
        }

        $url = $response->getInfo("redirect_url") ?? $response->getInfo('url');
        $uri = Uri::createFromString($url);
        $endpoint = Uri::createFromString($endpoint);

        if (!UriInfo::isAbsolute($endpoint)) {
            return (string) UriResolver::resolve($endpoint, $uri);
        }

        return (string) $endpoint;
    }

    private static function parseBody(ResponseInterface $response) : string | null {
        $doc = new Crawler($response->getContent());
        $webmentions = $doc->filter('[rel="webmention"][href]');

        if ($webmentions->count()) {
            return $webmentions->first()->attr('href');
        }

        return null;
    }
}