<?php

    namespace Socialbox\Classes;

    use Socialbox\Exceptions\DatabaseOperationException;
    use Socialbox\Exceptions\ResolutionException;
    use Socialbox\Managers\ResolvedServersManager;
    use Socialbox\Objects\ResolvedServer;

    class ServerResolver
    {
        private const string PATTERN = '/v=socialbox;sb-rpc=(https?:\/\/[^;]+);sb-key=([^;]+)/';

        /**
         * Resolves a given domain to fetch the RPC endpoint and public key from its DNS TXT records.
         *
         * @param string $domain The domain to be resolved.
         * @return ResolvedServer An instance of ResolvedServer containing the endpoint and public key.
         * @throws ResolutionException If the DNS TXT records cannot be resolved or if required information is missing.
         * @throws DatabaseOperationException
         */
        public static function resolveDomain(string $domain, bool $useDatabase=true): ResolvedServer
        {
            // First query the database to check if the domain is already resolved
            if($useDatabase)
            {
                $resolvedServer = ResolvedServersManager::getResolvedServer($domain);
                if($resolvedServer !== null)
                {
                    return $resolvedServer->toResolvedServer();
                }
            }

            $txtRecords = self::dnsGetTxtRecords($domain);
            if ($txtRecords === false)
            {
                throw new ResolutionException(sprintf("Failed to resolve DNS TXT records for %s", $domain));
            }

            $fullRecord = self::concatenateTxtRecords($txtRecords);
            if (preg_match(self::PATTERN, $fullRecord, $matches))
            {
                $endpoint = trim($matches[1]);
                $publicKey = trim(str_replace(' ', '', $matches[2]));
                if (empty($endpoint))
                {
                    throw new ResolutionException(sprintf("Failed to resolve RPC endpoint for %s", $domain));
                }
                if (empty($publicKey))
                {
                    throw new ResolutionException(sprintf("Failed to resolve public key for %s", $domain));
                }
                return new ResolvedServer($endpoint, $publicKey);
            }
            else
            {
                throw new ResolutionException(sprintf("Failed to find valid SocialBox record for %s", $domain));
            }
        }

        /**
         * Retrieves the TXT records for a given domain using the dns_get_record function.
         *
         * @param string $domain The domain name to fetch TXT records for.
         * @return array|false An array of DNS TXT records on success, or false on failure.
         */
        private static function dnsGetTxtRecords(string $domain)
        {
            return dns_get_record($domain, DNS_TXT);
        }

        /**
         * Concatenates an array of TXT records into a single string, filtering for SocialBox records.
         *
         * @param array $txtRecords An array of TXT records, where each record is expected to have a 'txt' key.
         * @return string A concatenated string of all relevant TXT records.
         */
        private static function concatenateTxtRecords(array $txtRecords): string
        {
            $fullRecordBuilder = '';
            foreach ($txtRecords as $txt)
            {
                if (isset($txt['txt']))
                {
                    $record = trim($txt['txt'], '" ');
                    // Only include records that start with v=socialbox
                    if (stripos($record, 'v=socialbox') === 0)
                    {
                        $fullRecordBuilder .= $record;
                    }
                }
            }
            return $fullRecordBuilder;
        }
    }