<?php


require_once __DIR__ . '/../includes/api-helpers.php';

header('Content-Type: application/json; charset=utf-8');
header('Access-Control-Allow-Origin: *');
header('Access-Control-Allow-Methods: GET, OPTIONS');
header('Access-Control-Allow-Headers: Content-Type');

if ($_SERVER['REQUEST_METHOD'] === 'OPTIONS') {
    http_response_code(200);
    exit;
}

if (!checkApiRateLimit('reverse-dns')) {
    rejectApiRateLimit();
}

$ip = isset($_GET['ip']) ? trim($_GET['ip']) : '';

if (empty($ip)) {
    http_response_code(400);
    echo json_encode(['error' => 'IP-Parameter fehlt']);
    exit;
}


$isIPv4 = filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4);
$isIPv6 = filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6);

if (!$isIPv4 && !$isIPv6) {
    http_response_code(400);
    echo json_encode(['error' => 'Ungültiges IP-Format']);
    exit;
}

$startTime = microtime(true);
$result = performReverseLookup($ip, $isIPv6 ? 'IPv6' : 'IPv4');
$queryTime = round((microtime(true) - $startTime) * 1000, 2);

echo json_encode([
    'success' => true,
    'ip' => $ip,
    'ip_version' => $isIPv6 ? 'IPv6' : 'IPv4',
    'query_time_ms' => $queryTime,
    'timestamp' => date('Y-m-d H:i:s'),
    'result' => $result
], JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE);


function performReverseLookup(string $ip, string $version): array {
    $result = [
        'hostname' => null,
        'ptr_record' => null,
        'additional_info' => []
    ];
    
    
    $hostname = @gethostbyaddr($ip);
    
    if ($hostname && $hostname !== $ip) {
        $result['hostname'] = $hostname;
        
        
        $forwardIp = gethostbyname($hostname);
        $result['forward_verified'] = ($forwardIp === $ip);
        
        
        $result['additional_info'] = getHostInfo($hostname);
    } else {
        $result['error'] = 'Kein PTR-Record gefunden';
    }
    
    
    $ptrRecord = getPtrRecord($ip, $version);
    if ($ptrRecord) {
        $result['ptr_record'] = $ptrRecord;
    }
    
    
    $result['ip_info'] = getIpInfo($ip);
    
    return $result;
}


function getPtrRecord(string $ip, string $version): ?string {
    if ($version === 'IPv4') {
        
        $parts = array_reverse(explode('.', $ip));
        $ptrDomain = implode('.', $parts) . '.in-addr.arpa';
    } else {
        
        $expanded = expandIPv6($ip);
        $nibbles = str_replace(':', '', $expanded);
        $reversed = implode('.', array_reverse(str_split($nibbles)));
        $ptrDomain = $reversed . '.ip6.arpa';
    }
    
    $records = @dns_get_record($ptrDomain, DNS_PTR);
    
    if ($records && !empty($records[0]['target'])) {
        return $records[0]['target'];
    }
    
    return null;
}


function expandIPv6(string $ip): string {
    
    if (strpos($ip, '::') !== false) {
        $parts = explode('::', $ip);
        $left = $parts[0] ? explode(':', $parts[0]) : [];
        $right = isset($parts[1]) && $parts[1] ? explode(':', $parts[1]) : [];
        $missing = 8 - count($left) - count($right);
        $middle = array_fill(0, $missing, '0000');
        $all = array_merge($left, $middle, $right);
    } else {
        $all = explode(':', $ip);
    }
    
    
    $all = array_map(function($segment) {
        return str_pad($segment, 4, '0', STR_PAD_LEFT);
    }, $all);
    
    return implode(':', $all);
}


function getHostInfo(string $hostname): array {
    $info = [];
    
    
    $parts = explode('.', $hostname);
    $tld = end($parts);
    
    $info['tld'] = $tld;
    
    
    $providerPatterns = [
        'amazonaws.com' => 'Amazon AWS',
        'googleusercontent.com' => 'Google Cloud',
        'cloudfront.net' => 'Amazon CloudFront',
        'azure' => 'Microsoft Azure',
        'hetzner' => 'Hetzner',
        'ovh' => 'OVH',
        'digitalocean' => 'DigitalOcean',
        'linode' => 'Linode',
        'vultr' => 'Vultr',
        'contabo' => 'Contabo',
        'netcup' => 'Netcup',
        'strato' => 'Strato',
        'ionos' => 'IONOS',
        '1und1' => '1&1',
        'telekom' => 'Deutsche Telekom',
        'vodafone' => 'Vodafone',
    ];
    
    foreach ($providerPatterns as $pattern => $provider) {
        if (stripos($hostname, $pattern) !== false) {
            $info['provider'] = $provider;
            break;
        }
    }
    
    return $info;
}


function getIpInfo(string $ip): array {
    $info = [
        'type' => 'unknown'
    ];
    
    
    if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4)) {
        if (preg_match('/^(10\.|172\.(1[6-9]|2[0-9]|3[01])\.|192\.168\.)/', $ip)) {
            $info['type'] = 'private';
        } elseif (preg_match('/^(127\.)/', $ip)) {
            $info['type'] = 'loopback';
        } else {
            $info['type'] = 'public';
        }
    } else {
        
        if (preg_match('/^(fc|fd)/i', $ip)) {
            $info['type'] = 'private';
        } elseif (preg_match('/^::1$/', $ip) || preg_match('/^fe80:/i', $ip)) {
            $info['type'] = 'loopback/link-local';
        } else {
            $info['type'] = 'public';
        }
    }
    
    return $info;
}