<?php

declare(strict_types=1);

session_set_cookie_params([
    'httponly' => true,
    'samesite' => 'Strict',
    'secure' => !empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off',
    'use_strict_mode' => true,
]);
session_start();
if ((int) ($_SERVER['CONTENT_LENGTH'] ?? 0) > 1048576) {
    http_response_code(413);
    exit('Anfrage zu groß.');
}
header('Cache-Control: no-store');
header('X-Content-Type-Options: nosniff');
header('X-Frame-Options: DENY');
header('Referrer-Policy: no-referrer');
header('Permissions-Policy: camera=(), microphone=(), geolocation=()');
header("Content-Security-Policy: default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; base-uri 'self'; form-action 'self'; frame-ancestors 'none'");

require_once __DIR__ . '/inc/db.inc.php';
require_once __DIR__ . '/inc/mail.inc.php';

if ($_SERVER['REQUEST_METHOD'] !== 'POST') {
    http_response_code(405);
    header('Allow: POST');
    exit('Methode nicht erlaubt.');
}

$submittedCsrf = $_POST['csrf_token'] ?? '';
$storedCsrf = $_SESSION['registration_csrf'] ?? '';
if (!is_string($submittedCsrf) || $storedCsrf === '' || !hash_equals($storedCsrf, $submittedCsrf)) {
    http_response_code(403);
    exit('Ungültige Anfrage.');
}
unset($_SESSION['registration_csrf']);

function postString(string $key): string
{
    $value = $_POST[$key] ?? '';

    return is_string($value) ? trim($value) : '';
}

function postStringList(string $key): array
{
    $value = $_POST[$key] ?? [];
    $values = is_array($value) ? $value : [$value];

    return array_values(array_filter(
        array_map(
            static fn ($item): string => is_string($item) ? trim($item) : '',
            $values
        ),
        static fn (string $item): bool => $item !== ''
    ));
}

function postMealSelectionsByDay(): array
{
    $value = $_POST['meals'] ?? [];
    if (!is_array($value)) {
        return [];
    }

    $result = [];
    foreach ($value as $day => $meals) {
        if (!is_array($meals)) {
            continue;
        }
        $result[(string) $day] = array_values(array_filter(
            array_map(static fn ($item): string => is_string($item) ? trim($item) : '', $meals),
            static fn (string $item): bool => $item !== ''
        ));
    }

    return $result;
}

function formatMealSummary(array $days, array $mealsByDay): string
{
    $dayLabels = ['1' => 'Fr.', '2' => 'Sa.', '3' => 'So.'];
    $mealLabels = [
        'breakfast' => 'Frühstück',
        'lunch' => 'Mittagessen',
        'coffee' => 'Kaffee',
        'dinner' => 'Abendessen',
        'drinks' => 'Getränkepauschale',
    ];
    $parts = [];
    foreach ($days as $day) {
        $labels = array_map(static fn (string $meal): string => $mealLabels[$meal] ?? $meal, $mealsByDay[$day] ?? []);
        $labels[] = $mealLabels['drinks'];
        $labels[] = $mealLabels['rehearsal_room'];
        $parts[] = ($dayLabels[$day] ?? $day) . ': ' . implode(', ', $labels);
    }

    return implode('; ', $parts) ?: '–';
}

function escapeHtml(string $value): string
{
    return htmlspecialchars($value, ENT_QUOTES | ENT_SUBSTITUTE, 'UTF-8');
}

function smtpResponse($socket): string
{
    $response = '';
    do {
        $line = fgets($socket);
        if ($line === false) {
            throw new RuntimeException('Keine gültige SMTP-Antwort erhalten.');
        }
        $response .= $line;
    } while (isset($line[3]) && $line[3] === '-');

    return $response;
}

function smtpCommand($socket, string $command, array $expectedCodes): void
{
    fwrite($socket, $command . "\r\n");
    $response = smtpResponse($socket);
    $code = (int) substr($response, 0, 3);

    if (!in_array($code, $expectedCodes, true)) {
        throw new RuntimeException('SMTP-Befehl wurde abgelehnt.');
    }
}

function encodedHeader(string $value): string
{
    return '=?UTF-8?B?' . base64_encode($value) . '?=';
}

function calculateBookingTotal(PDO $pdo, bool $under27, string $guestType, ?string $roomType, array $mealsByDay): float
{
    $ageSuffix = $under27 ? 'under_27' : 'over_27';
    $keys = [];
    if ($guestType === 'regular_guest' && $roomType !== null) {
        $keys[] = $roomType . '_' . $ageSuffix;
    }
    if ($guestType === 'day_guest') {
        foreach ($mealsByDay as $meals) {
            foreach (array_unique(array_merge($meals, ['drinks'])) as $meal) {
                if (in_array($meal, ['breakfast', 'lunch', 'coffee', 'dinner'], true)) {
                    $keys[] = $meal . '_' . $ageSuffix;
                } elseif ($meal === 'drinks') {
                    $keys[] = 'drinks';
                }
            }
            $keys[] = 'rehearsal_room';
        }
    }
    if ($keys === []) {
        return 0.0;
    }

    $uniqueKeys = array_values(array_unique($keys));
    $placeholders = implode(',', array_fill(0, count($uniqueKeys), '?'));
    $statement = $pdo->prepare("SELECT setting_key, price FROM pricing_settings WHERE setting_key IN ($placeholders)");
    $statement->execute($uniqueKeys);
    $prices = [];
    foreach ($statement->fetchAll(PDO::FETCH_ASSOC) as $row) {
        $prices[(string) $row['setting_key']] = (float) $row['price'];
    }

    return round(array_sum(array_map(
        static fn (string $key): float => $prices[$key] ?? 0.0,
        $keys
    )), 2);
}

function sendRegistrationEmail(
    array $mailConfig,
    string $recipient,
    string $name,
    string $participantPassword,
    string $guestType,
    bool $under27,
    ?string $roomType,
    array $days,
    array $mealsByDay,
    string $allergies,
    string $roommates,
    string $otherNotes
): void {
    $roomLabels = [
        'single' => 'Einzelzimmer',
        'double' => 'Doppelzimmer',
        'multi' => 'Mehrbettzimmer',
    ];
    $dayLabels = ['1' => 'Fr.', '2' => 'Sa.', '3' => 'So.'];
    $mealLabels = [
        'breakfast' => 'Frühstück',
        'lunch' => 'Mittagessen',
        'coffee' => 'Kaffee',
        'drinks' => 'Getränkepauschale',
        'dinner' => 'Abendessen',
        'rehearsal_room' => 'Proberaumpauschale',
    ];
    $guestLabel = $guestType === 'day_guest' ? 'Tagesgast' : 'Dauergast';
    $ageLabel = $under27 ? 'Unter 27' : 'Ab 27';
    $roomLabel = $roomLabels[$roomType ?? ''] ?? '–';
    $dayText = implode(', ', array_map(static fn (string $day): string => $dayLabels[$day] ?? $day, $days)) ?: '–';
    $mealText = formatMealSummary($days, $mealsByDay);
    $roommates = $roommates !== '' ? $roommates : '–';
    $allergies = $allergies !== '' ? $allergies : '–';
    $otherNotes = $otherNotes !== '' ? $otherNotes : '–';

    $textBody = "Hallo {$name},\n\n"
        . "deine Registrierung für das Chorwochenende wurde erfolgreich gespeichert.\n\n"
        . "Zugang zur Änderung oder Löschung:\n"
        . "E-Mail-Adresse: {$recipient}\n"
        . "Passwort: {$participantPassword}\n\n"
        . "Zusammenfassung:\n"
        . "Altersgruppe: {$ageLabel}\n"
        . "Gasttyp: {$guestLabel}\n"
        . "Zimmerart: {$roomLabel}\n"
        . "Anwesenheitstage: {$dayText}\n"
        . "Mahlzeiten: {$mealText}\n"
        . "Zimmerpartner-Wunsch: {$roommates}\n"
        . "Allergien / Essensvorlieben: {$allergies}\n"
        . "Sonstiges: {$otherNotes}\n\n"
        . "Viele Grüße\n{$mailConfig['from_name']}";

    $html = static fn (string $value): string => escapeHtml($value);
    $htmlBody = '<!doctype html><html lang="de"><body>'
        . '<p>Hallo ' . $html($name) . ',</p>'
        . '<p>deine Registrierung für das Chorwochenende wurde erfolgreich gespeichert.</p>'
        . '<h2>Deine Zugangsdaten</h2><p><strong>E-Mail-Adresse:</strong> ' . $html($recipient)
        . '<br><strong>Passwort:</strong> <code>' . $html($participantPassword) . '</code></p>'
        . '<h2>Zusammenfassung</h2><ul>'
        . '<li><strong>Altersgruppe:</strong> ' . $html($ageLabel) . '</li>'
        . '<li><strong>Gasttyp:</strong> ' . $html($guestLabel) . '</li>'
        . '<li><strong>Zimmerart:</strong> ' . $html($roomLabel) . '</li>'
        . '<li><strong>Anwesenheitstage:</strong> ' . $html($dayText) . '</li>'
        . '<li><strong>Mahlzeiten:</strong> ' . $html($mealText) . '</li>'
        . '<li><strong>Zimmerpartner-Wunsch:</strong> ' . $html($roommates) . '</li>'
        . '<li><strong>Allergien / Essensvorlieben:</strong> ' . $html($allergies) . '</li>'
        . '<li><strong>Sonstiges:</strong> ' . $html($otherNotes) . '</li></ul>'
        . '<p>Viele Grüße<br>' . $html($mailConfig['from_name']) . '</p></body></html>';

    $boundary = '=_cat_' . bin2hex(random_bytes(12));
    $message = 'From: ' . encodedHeader($mailConfig['from_name']) . ' <' . $mailConfig['from_address'] . ">\r\n"
        . 'To: ' . $recipient . "\r\n"
        . 'Subject: ' . encodedHeader('Deine Registrierung für das Chorwochenende') . "\r\n"
        . "MIME-Version: 1.0\r\n"
        . 'Content-Type: multipart/alternative; boundary="' . $boundary . "\"\r\n\r\n"
        . '--' . $boundary . "\r\nContent-Type: text/plain; charset=UTF-8\r\nContent-Transfer-Encoding: 8bit\r\n\r\n"
        . $textBody . "\r\n\r\n"
        . '--' . $boundary . "\r\nContent-Type: text/html; charset=UTF-8\r\nContent-Transfer-Encoding: 8bit\r\n\r\n"
        . $htmlBody . "\r\n\r\n"
        . '--' . $boundary . "--\r\n";

    $context = stream_context_create([
        'ssl' => [
            'peer_name' => $mailConfig['host'],
            'verify_peer' => true,
            'verify_peer_name' => true,
        ],
    ]);
    $socket = stream_socket_client(
        'tcp://' . $mailConfig['host'] . ':' . $mailConfig['port'],
        $errorNumber,
        $errorMessage,
        20,
        STREAM_CLIENT_CONNECT,
        $context
    );
    if ($socket === false) {
        throw new RuntimeException('SMTP-Server nicht erreichbar.');
    }
    stream_set_timeout($socket, 20);

    try {
        $response = smtpResponse($socket);
        if ((int) substr($response, 0, 3) !== 220) {
            throw new RuntimeException('SMTP-Verbindung wurde abgelehnt.');
        }
        smtpCommand($socket, 'EHLO localhost', [250]);
        smtpCommand($socket, 'STARTTLS', [220]);
        if (!stream_socket_enable_crypto($socket, true, STREAM_CRYPTO_METHOD_TLS_CLIENT)) {
            throw new RuntimeException('STARTTLS konnte nicht aktiviert werden.');
        }
        smtpCommand($socket, 'EHLO localhost', [250]);
        smtpCommand($socket, 'AUTH LOGIN', [334]);
        smtpCommand($socket, base64_encode($mailConfig['username']), [334]);
        smtpCommand($socket, base64_encode($mailConfig['password']), [235]);
        smtpCommand($socket, 'MAIL FROM:<' . $mailConfig['from_address'] . '>', [250]);
        smtpCommand($socket, 'RCPT TO:<' . $recipient . '>', [250, 251]);
        smtpCommand($socket, 'DATA', [354]);
        $message = preg_replace('/^\./m', '..', $message);
        fwrite($socket, $message . "\r\n.\r\n");
        $response = smtpResponse($socket);
        if ((int) substr($response, 0, 3) !== 250) {
            throw new RuntimeException('E-Mail konnte nicht angenommen werden.');
        }
        fwrite($socket, "QUIT\r\n");
    } finally {
        fclose($socket);
    }
}

function sendAdminNotificationEmail(
    array $mailConfig,
    string $recipient,
    string $name,
    string $participantEmail,
    string $guestLabel,
    string $ageLabel,
    string $roomLabel,
    string $dayText,
    string $mealText,
    string $roommates,
    string $allergies,
    string $otherNotes
): void {
    $textBody = "Neue Registrierung für das Chorwochenende\n\n"
        . "Name: {$name}\n"
        . "E-Mail: {$participantEmail}\n"
        . "Altersgruppe: {$ageLabel}\n"
        . "Gasttyp: {$guestLabel}\n"
        . "Zimmerart: {$roomLabel}\n"
        . "Anwesenheitstage: {$dayText}\n"
        . "Mahlzeiten: {$mealText}\n"
        . "Zimmerpartner-Wunsch: {$roommates}\n"
        . "Allergien / Essensvorlieben: {$allergies}\n"
        . "Sonstiges: {$otherNotes}\n";
    $subject = encodedHeader('Neue Registrierung – Chorwochenende');
    $message = 'From: ' . encodedHeader($mailConfig['from_name']) . ' <' . $mailConfig['from_address'] . ">\r\n"
        . 'To: ' . $recipient . "\r\n"
        . 'Subject: ' . $subject . "\r\n"
        . "MIME-Version: 1.0\r\n"
        . "Content-Type: text/plain; charset=UTF-8\r\n"
        . "Content-Transfer-Encoding: 8bit\r\n\r\n"
        . $textBody;

    $context = stream_context_create([
        'ssl' => [
            'peer_name' => $mailConfig['host'],
            'verify_peer' => true,
            'verify_peer_name' => true,
        ],
    ]);
    $socket = stream_socket_client(
        'tcp://' . $mailConfig['host'] . ':' . $mailConfig['port'],
        $errorNumber,
        $errorMessage,
        20,
        STREAM_CLIENT_CONNECT,
        $context
    );
    if ($socket === false) {
        throw new RuntimeException('SMTP-Server nicht erreichbar.');
    }
    stream_set_timeout($socket, 20);

    try {
        $response = smtpResponse($socket);
        if ((int) substr($response, 0, 3) !== 220) {
            throw new RuntimeException('SMTP-Verbindung wurde abgelehnt.');
        }
        smtpCommand($socket, 'EHLO localhost', [250]);
        smtpCommand($socket, 'STARTTLS', [220]);
        if (!stream_socket_enable_crypto($socket, true, STREAM_CRYPTO_METHOD_TLS_CLIENT)) {
            throw new RuntimeException('STARTTLS konnte nicht aktiviert werden.');
        }
        smtpCommand($socket, 'EHLO localhost', [250]);
        smtpCommand($socket, 'AUTH LOGIN', [334]);
        smtpCommand($socket, base64_encode($mailConfig['username']), [334]);
        smtpCommand($socket, base64_encode($mailConfig['password']), [235]);
        smtpCommand($socket, 'MAIL FROM:<' . $mailConfig['from_address'] . '>', [250]);
        smtpCommand($socket, 'RCPT TO:<' . $recipient . '>', [250, 251]);
        smtpCommand($socket, 'DATA', [354]);
        fwrite($socket, preg_replace('/^\./m', '..', $message) . "\r\n.\r\n");
        $response = smtpResponse($socket);
        if ((int) substr($response, 0, 3) !== 250) {
            throw new RuntimeException('E-Mail konnte nicht angenommen werden.');
        }
        fwrite($socket, "QUIT\r\n");
    } finally {
        fclose($socket);
    }
}

$name = postString('name');
$email = postString('email');
$under27 = isset($_POST['under_27']) && $_POST['under_27'] === '1';
$guestType = postString('guest_type');
$roomType = postString('room_type');
$roommates = postString('roommates');
$earlyDeparture = postString('early_departure');
$allergies = postString('allergies');
$otherNotes = postString('other_notes');
$days = postStringList('days');
$mealsByDay = postMealSelectionsByDay();

$errors = [];
$allowedDays = ['1', '2', '3'];
$allowedEarlyDepartures = [
    'sat_breakfast',
    'sat_lunch',
    'sat_coffee',
    'sat_dinner',
    'sun_breakfast',
];
$allowedMealsByDay = [
    '1' => ['dinner'],
    '2' => ['breakfast', 'lunch', 'coffee', 'dinner'],
    '3' => ['breakfast', 'lunch'],
];
$days = array_values(array_unique($days));
foreach ($mealsByDay as $day => $dayMeals) {
    $mealsByDay[$day] = array_values(array_unique($dayMeals));
}

if (count($days) > count($allowedDays) || array_diff($days, $allowedDays) !== []) {
    $errors[] = 'Bitte nur gültige Anwesenheitstage auswählen.';
}
if (array_diff(array_keys($mealsByDay), $allowedDays) !== []) {
    $errors[] = 'Bitte nur gültige Mahlzeitentage auswählen.';
}
foreach ($mealsByDay as $day => $dayMeals) {
    $allowedMeals = $allowedMealsByDay[(string) $day] ?? [];
    if (array_diff($dayMeals, $allowedMeals) !== []) {
        $errors[] = 'Bitte nur gültige Mahlzeiten auswählen.';
    }
    if (!in_array((string) $day, $days, true) && $dayMeals !== []) {
        $errors[] = 'Mahlzeiten dürfen nur für ausgewählte Anwesenheitstage angegeben werden.';
    }
}
foreach ($days as $day) {
    $mealsByDay[$day] ??= [];
}
if (mb_strlen($roommates) > 1000 || mb_strlen($allergies) > 1000) {
    $errors[] = 'Zimmerwunsch und Allergieangaben dürfen höchstens 1000 Zeichen enthalten.';
}

if ($name === '' || mb_strlen($name) > 255) {
    $errors[] = 'Bitte einen gültigen Namen eingeben.';
}

if (!filter_var($email, FILTER_VALIDATE_EMAIL) || mb_strlen($email) > 255) {
    $errors[] = 'Bitte eine gültige E-Mail-Adresse eingeben.';
}

if ($otherNotes !== '' && mb_strlen($otherNotes) > 5000) {
    $errors[] = 'Das Feld Sonstiges darf höchstens 5000 Zeichen enthalten.';
}

if (!in_array($guestType, ['day_guest', 'regular_guest'], true)) {
    $errors[] = 'Bitte einen gültigen Gasttyp auswählen.';
}

if ($guestType === 'regular_guest' && !in_array($roomType, ['single', 'double', 'multi'], true)) {
    $errors[] = 'Bitte eine gültige Zimmerart auswählen.';
}
if ($earlyDeparture !== '' && ($guestType !== 'regular_guest' || !in_array($earlyDeparture, $allowedEarlyDepartures, true))) {
    $errors[] = 'Bitte einen gültigen Abreisezeitpunkt auswählen.';
}

if ($errors !== []) {
    http_response_code(422);
    exit(implode("\n", $errors));
}

$roommateEligible = $guestType === 'regular_guest' && in_array($roomType, ['double', 'multi'], true);
if (!$roommateEligible) {
    $roommates = '';
}

$role = $guestType === 'day_guest' ? 'Tagesgast' : 'Dauergast';
$bookingType = $guestType === 'day_guest' ? 'Day' : 'Stay';
$accommodationType = $guestType === 'regular_guest' ? $roomType : null;
$roommateRequest = $roommateEligible && $roommates !== '' ? $roommates : null;
$earlyDeparture = $guestType === 'regular_guest' && in_array($earlyDeparture, $allowedEarlyDepartures, true)
    ? $earlyDeparture
    : null;

$mealPreferences = null;
if ($guestType === 'day_guest') {
    $mealPreferences = json_encode(
        [
            'days' => $days,
            'meals_by_day' => $mealsByDay,
        ],
        JSON_UNESCAPED_UNICODE | JSON_THROW_ON_ERROR
    );
}

$participantId = sprintf(
    '%s-%s-%s-%s-%s',
    bin2hex(random_bytes(4)),
    bin2hex(random_bytes(2)),
    bin2hex(random_bytes(2)),
    bin2hex(random_bytes(2)),
    bin2hex(random_bytes(6))
);
$participantPassword = bin2hex(random_bytes(8));
$participantPasswordHash = password_hash($participantPassword, PASSWORD_DEFAULT);

try {
    $dsn = sprintf(
        'mysql:host=%s;port=%d;dbname=%s;charset=%s',
        $dbConfig['host'],
        $dbConfig['port'],
        $dbConfig['database'],
        $dbConfig['charset']
    );

    $pdo = new PDO($dsn, $dbConfig['username'], $dbConfig['password'], [
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION,
        PDO::ATTR_EMULATE_PREPARES => false,
    ]);

    $totalPrice = calculateBookingTotal($pdo, $under27, $guestType, $accommodationType, $mealsByDay);

    $pdo->beginTransaction();

    $participantStatement = $pdo->prepare(
        'INSERT INTO participants (id, name, email, allergies, role, under_27, password_hash)
         VALUES (:id, :name, :email, :allergies, :role, :under_27, :password_hash)'
    );
    $participantStatement->execute([
        ':id' => $participantId,
        ':name' => $name,
        ':email' => $email,
        ':allergies' => $allergies !== '' ? $allergies : null,
        ':role' => $role,
        ':under_27' => $under27 ? 1 : 0,
        ':password_hash' => $participantPasswordHash,
    ]);

    $bookingStatement = $pdo->prepare(
        'INSERT INTO bookings
            (participant_id, type, accommodation_type, meal_preferences, roommate_requests, early_departure, other_notes, total_price)
         VALUES
            (:participant_id, :type, :accommodation_type, :meal_preferences, :roommate_requests, :early_departure, :other_notes, :total_price)'
    );
    $bookingStatement->execute([
        ':participant_id' => $participantId,
        ':type' => $bookingType,
        ':accommodation_type' => $accommodationType,
        ':meal_preferences' => $mealPreferences,
        ':roommate_requests' => $roommateRequest,
        ':early_departure' => $earlyDeparture,
        ':other_notes' => $otherNotes !== '' ? $otherNotes : null,
        ':total_price' => number_format($totalPrice, 2, '.', ''),
    ]);

    $pdo->commit();

    $mailError = '';
    try {
        sendRegistrationEmail(
            $mailConfig,
            $email,
            $name,
            $participantPassword,
            $guestType,
            $under27,
            $roomType,
            $days,
            $mealsByDay,
            $allergies,
            $roommates,
            $otherNotes
        );
    } catch (Throwable $exception) {
        error_log('Registrierung gespeichert, E-Mail konnte nicht versendet werden: ' . $exception->getMessage());
        $mailError = '<p class="message error">Die Registrierung wurde gespeichert, aber die Bestätigungs-E-Mail konnte nicht versendet werden. Bitte bewahre die Zugangsdaten auf dieser Seite auf.</p>';
    }

    $roomLabels = ['single' => 'Einzelzimmer', 'double' => 'Doppelzimmer', 'multi' => 'Mehrbettzimmer'];
    $dayLabels = ['1' => 'Fr.', '2' => 'Sa.', '3' => 'So.'];
    $mealLabels = [
        'breakfast' => 'Frühstück',
        'lunch' => 'Mittagessen',
        'coffee' => 'Kaffee',
        'drinks' => 'Getränkepauschale',
        'dinner' => 'Abendessen',
        'rehearsal_room' => 'Proberaumpauschale',
    ];
    $guestLabel = $guestType === 'day_guest' ? 'Tagesgast' : 'Dauergast';
    $ageLabel = $under27 ? 'Unter 27' : 'Ab 27';
    $roomLabel = $roomLabels[$roomType] ?? '–';
    $dayText = implode(', ', array_map(static fn (string $day): string => $dayLabels[$day] ?? $day, $days)) ?: '–';
    $mealText = formatMealSummary($days, $mealsByDay);
    $adminEmails = $pdo->query(
        "SELECT email FROM admin_users WHERE is_active = 1 AND email <> ''"
    )->fetchAll(PDO::FETCH_COLUMN);
    foreach ($adminEmails as $adminEmail) {
        if (!is_string($adminEmail) || !filter_var($adminEmail, FILTER_VALIDATE_EMAIL)) {
            continue;
        }
        try {
            sendAdminNotificationEmail(
                $mailConfig,
                (string) $adminEmail,
                $name,
                $email,
                $guestLabel,
                $ageLabel,
                $roomLabel,
                $dayText,
                $mealText,
                $roommates !== '' ? $roommates : '–',
                $allergies !== '' ? $allergies : '–',
                $otherNotes !== '' ? $otherNotes : '–'
            );
        } catch (Throwable $exception) {
            error_log('Admin-Benachrichtigung konnte nicht versendet werden: ' . $exception->getMessage());
        }
    }

    http_response_code(201);
    $safeEmail = escapeHtml($email);
    $safePassword = escapeHtml($participantPassword);
    exit(<<<HTML
<!DOCTYPE html>
<html lang="de">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Registrierung erfolgreich</title>
    <link rel="stylesheet" href="./css/booking.css">
</head>
<body>
    <main class="success-card">
        <h1>Registrierung erfolgreich</h1>
        {$mailError}
        <p>Bitte bewahre die folgenden Zugangsdaten auf. Du benötigst sie, um deine Registrierung später zu ändern oder zu löschen.</p>
        <dl class="credentials">
            <dt>E-Mail-Adresse</dt>
            <dd>{$safeEmail}</dd>
            <dt>Passwort</dt>
            <dd><code>{$safePassword}</code></dd>
        </dl>
        <p><a href="edit_registration.php">Registrierung ändern oder löschen</a></p>
        <p><a href="index.php">Zur Startseite</a></p>
    </main>
</body>
</html>
HTML);
} catch (Throwable $exception) {
    if (isset($pdo) && $pdo->inTransaction()) {
        $pdo->rollBack();
    }

    error_log($exception->getMessage());
    if ($exception instanceof PDOException && $exception->getCode() === '23000'
        && str_contains($exception->getMessage(), "for key 'email'")) {
        http_response_code(409);
        exit('Diese E-Mail-Adresse ist bereits registriert. Bitte nutze die Änderungs- oder Löschfunktion deiner bestehenden Registrierung.');
    }

    http_response_code(500);
    exit('Die Registrierung konnte nicht gespeichert werden.');
}