<?php

declare(strict_types=1);

function bookingDatabaseUrl(?string $environmentUrl = null, ?string $configurationFile = null): string
{
    $url = $environmentUrl ?? getenv('DATABASE_URL');
    if (!is_string($url) || trim($url) === '') {
        $configurationFile ??= dirname(__DIR__, 2).'/booking-config.php';
        if (is_file($configurationFile)) {
            $configuration = require $configurationFile;
            $url = is_array($configuration) ? ($configuration['database_url'] ?? '') : '';
        }
    }
    if (!is_string($url) || trim($url) === '') {
        throw new RuntimeException('DATABASE_URL is not configured and the booking configuration file does not contain a database URL.');
    }
    return trim($url);
}

function bookingDatabase(): PDO
{
    $url = bookingDatabaseUrl();
    $parts = is_string($url) ? parse_url($url) : false;
    if (!is_array($parts) || ($parts['scheme'] ?? '') !== 'mysql' || !isset($parts['host'], $parts['path'], $parts['user'])) {
        throw new RuntimeException('DATABASE_URL is not configured correctly.');
    }
    $dsn = sprintf('mysql:host=%s;port=%d;dbname=%s;charset=utf8mb4', $parts['host'], (int) ($parts['port'] ?? 3306), ltrim($parts['path'], '/'));
    return new PDO($dsn, rawurldecode($parts['user']), rawurldecode($parts['pass'] ?? ''), [PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION, PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC, PDO::ATTR_EMULATE_PREPARES => false]);
}

function bookingBaseUrl(): string
{
    $configured = getenv('BOOKING_BASE_URL');
    if (is_string($configured) && $configured !== '') {
        return rtrim($configured, '/');
    }
    $scheme = (!empty($_SERVER['HTTPS']) && $_SERVER['HTTPS'] !== 'off') ? 'https' : 'http';
    return $scheme.'://'.($_SERVER['HTTP_HOST'] ?? 'localhost');
}

function bookingUuid(): string
{
    $hex = bin2hex(random_bytes(16));
    return sprintf('%s-%s-%s-%s-%s', substr($hex, 0, 8), substr($hex, 8, 4), substr($hex, 12, 4), substr($hex, 16, 4), substr($hex, 20));
}

function bookingProjectIsValid(string $project): bool
{
    return in_array($project, ['perspektivwerk', 'produktionsschule'], true);
}

function bookingProjectTitle(string $project): string
{
    return $project === 'produktionsschule' ? 'Produktionsschule' : 'PerspektivWerk';
}

function bookingMailTransport(?string $configuredTransport = null): string
{
    $transport = $configuredTransport ?? getenv('BOOKING_MAIL_TRANSPORT');
    if (!is_string($transport) || $transport === '') return 'sendmail';
    return $transport;
}

function bookingIcsCalendar(array $event): string
{
    $timezone = new DateTimeZone('Europe/Berlin');
    $utc = new DateTimeZone('UTC');
    $start = new DateTimeImmutable((string) $event['starts_at'], $timezone);
    $end = new DateTimeImmutable((string) $event['ends_at'], $timezone);
    $lines = [
        'BEGIN:VCALENDAR', 'VERSION:2.0', 'PRODID:-//SUFW//Terminbuchung//DE', 'CALSCALE:GREGORIAN',
        'BEGIN:VEVENT',
        'UID:'.bookingIcsEscape((string) $event['id']).'@sufw-booking',
        'DTSTAMP:'.gmdate('Ymd\\THis\\Z'),
        'DTSTART:'.$start->setTimezone($utc)->format('Ymd\\THis\\Z'),
        'DTEND:'.$end->setTimezone($utc)->format('Ymd\\THis\\Z'),
        'SUMMARY:'.bookingIcsEscape((string) $event['title']),
        'DESCRIPTION:'.bookingIcsEscape(($event['format'] ?? '') === 'telefonisch' ? 'Telefonischer Termin' : 'Termin vor Ort'),
        'END:VEVENT', 'END:VCALENDAR',
    ];
    return implode("\r\n", $lines)."\r\n";
}

function bookingSendMail(string $email, string $subject, string $textBody, ?string $calendar = null): void
{
    $transport = bookingMailTransport();
    if ($transport === 'disabled') return;
    if ($transport !== 'sendmail') throw new RuntimeException('Unsupported booking mail transport.');
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) throw new InvalidArgumentException('Invalid mail recipient.');

    $sender = 'sufw-buchung@boogiedev.net';
    $headers = ['From' => $sender, 'Reply-To' => $sender, 'MIME-Version' => '1.0'];
    if ($calendar === null) {
        $headers['Content-Type'] = 'text/plain; charset=UTF-8';
        $message = $textBody;
    } else {
        $boundary = '=_sufw_'.bin2hex(random_bytes(16));
        $headers['Content-Type'] = 'multipart/mixed; boundary="'.$boundary.'"';
        $message = '--'.$boundary."\r\n"
            ."Content-Type: text/plain; charset=UTF-8\r\nContent-Transfer-Encoding: 8bit\r\n\r\n"
            .$textBody."\r\n--".$boundary."\r\n"
            ."Content-Type: text/calendar; charset=UTF-8; method=PUBLISH; name=\"termin.ics\"\r\n"
            ."Content-Transfer-Encoding: base64\r\nContent-Disposition: attachment; filename=\"termin.ics\"\r\n\r\n"
            .chunk_split(base64_encode($calendar), 76, "\r\n")
            .'--'.$boundary."--\r\n";
    }
    if (!mail($email, $subject, $message, $headers, '-f'.$sender)) {
        throw new RuntimeException('The confirmation email could not be handed to sendmail.');
    }
}

function bookingNormaliseEvent(array $event): array
{
    $event['capacity'] = (int) $event['capacity'];
    $event['confirmedCount'] = (int) $event['confirmedCount'];
    $event['availableCapacity'] = max(0, $event['capacity'] - $event['confirmedCount']);
    $event['status'] = $event['availableCapacity'] > 0 ? 'available' : 'full';
    $event['introductionRequired'] = (bool) $event['introductionRequired'];
    unset($event['confirmedCount']);
    return $event;
}

function bookingListEvents(PDO $database, string $project, string $from, string $to): array
{
    $statement = $database->prepare(<<<'SQL'
        SELECT e.id, e.project, e.title, e.starts_at AS startsAt, e.ends_at AS endsAt, e.capacity,
               e.format, e.introduction_required AS introductionRequired, e.contact_name AS contactName,
               COUNT(r.id) AS confirmedCount
        FROM sufw_booking_events e
        LEFT JOIN sufw_booking_registrations r ON r.event_id = e.id AND r.status = 'confirmed'
        WHERE e.project = :project AND e.is_active = 1 AND e.starts_at < :toDate AND e.ends_at >= :fromDate
        GROUP BY e.id ORDER BY e.starts_at, e.title
        SQL);
    $statement->execute(['project' => $project, 'fromDate' => "$from 00:00:00", 'toDate' => "$to 00:00:00"]);
    return array_map('bookingNormaliseEvent', $statement->fetchAll());
}

function bookingCreateRegistration(PDO $database, array $payload): array
{
    $project = (string) ($payload['project'] ?? '');
    $eventId = (string) ($payload['eventId'] ?? '');
    $name = trim((string) ($payload['name'] ?? ''));
    $email = mb_strtolower(trim((string) ($payload['email'] ?? '')));
    $phone = trim((string) ($payload['phone'] ?? ''));
    $privacyAccepted = ($payload['privacyAccepted'] ?? false) === true;
    $introductionAttended = ($payload['introductionAttended'] ?? false) === true;
    $introductionDate = trim((string) ($payload['introductionDate'] ?? ''));
    if (!bookingProjectIsValid($project) || !preg_match('/^[a-f0-9-]{36}$/', $eventId) || $name === '' || mb_strlen($name) > 160 || !filter_var($email, FILTER_VALIDATE_EMAIL) || mb_strlen($email) > 254 || !preg_match('/^[0-9+()\-\/\s]{6,64}$/', $phone) || !$privacyAccepted) {
        throw new InvalidArgumentException('Bitte prüfen Sie Ihre Pflichtangaben.');
    }
    if ($introductionDate !== '' && (!preg_match('/^\d{4}-\d{2}-\d{2}$/', $introductionDate) || !DateTimeImmutable::createFromFormat('!Y-m-d', $introductionDate))) {
        throw new InvalidArgumentException('Bitte prüfen Sie das Datum der Einführungsveranstaltung.');
    }

    $database->beginTransaction();
    try {
        $eventStatement = $database->prepare('SELECT * FROM sufw_booking_events WHERE id = :id AND project = :project AND is_active = 1 FOR UPDATE');
        $eventStatement->execute(['id' => $eventId, 'project' => $project]);
        $event = $eventStatement->fetch();
        if (!$event) throw new OutOfBoundsException('Dieser Termin ist nicht mehr verfügbar.');
        if ((bool) $event['introduction_required'] && (!$introductionAttended || $introductionDate === '')) {
            throw new InvalidArgumentException('Bitte bestätigen Sie die Einführungsveranstaltung und geben Sie das Datum an.');
        }
        $confirmed = $database->prepare("SELECT COUNT(*) FROM sufw_booking_registrations WHERE event_id = :eventId AND status = 'confirmed'");
        $confirmed->execute(['eventId' => $eventId]);
        if ((int) $confirmed->fetchColumn() >= (int) $event['capacity']) throw new RuntimeException('Dieser Termin ist inzwischen ausgebucht.');
        $duplicate = $database->prepare("SELECT id FROM sufw_booking_registrations WHERE event_id = :eventId AND email = :email AND name = :name AND status IN ('pending_confirmation', 'confirmed') LIMIT 1");
        $duplicate->execute(['eventId' => $eventId, 'email' => $email, 'name' => $name]);
        if ($duplicate->fetch()) throw new LogicException('Für diese Person liegt bereits eine Anmeldung für diesen Termin vor.');

        $registrationId = bookingUuid();
        $token = bin2hex(random_bytes(32));
        $insert = $database->prepare(<<<'SQL'
            INSERT INTO sufw_booking_registrations
              (id, event_id, status, name, email, phone, privacy_accepted_at, confirmation_token_hash, confirmation_expires_at, introduction_attended, introduction_date)
            VALUES
              (:id, :eventId, 'pending_confirmation', :name, :email, :phone, UTC_TIMESTAMP(), :tokenHash, DATE_ADD(UTC_TIMESTAMP(), INTERVAL 30 MINUTE), :introductionAttended, :introductionDate)
            SQL);
        $insert->execute(['id' => $registrationId, 'eventId' => $eventId, 'name' => $name, 'email' => $email, 'phone' => $phone, 'tokenHash' => hash('sha256', $token), 'introductionAttended' => $introductionAttended ? 1 : 0, 'introductionDate' => $introductionAttended ? $introductionDate : null]);
        $link = bookingBaseUrl().'/booking/confirm.php?token='.rawurlencode($token);
        $subject = 'Bitte bestätigen Sie Ihre Terminanfrage';
        $body = "Guten Tag $name,\n\nbitte bestätigen Sie Ihre Anfrage für \"{$event['title']}\" am {$event['starts_at']} innerhalb von 30 Minuten:\n$link\n\nKontakt für Rückfragen: {$event['contact_name']} ({$event['contact_email']}).";
        $database->commit();
        bookingSendMail($email, $subject, $body);
        return ['registrationId' => $registrationId, 'expiresAt' => gmdate('c', time() + 1800)];
    } catch (Throwable $exception) {
        if ($database->inTransaction()) $database->rollBack();
        throw $exception;
    }
}

function bookingConfirmRegistration(PDO $database, string $token): array
{
    if (!preg_match('/^[a-f0-9]{64}$/', $token)) throw new InvalidArgumentException('Der Bestätigungslink ist ungültig.');
    $database->beginTransaction();
    try {
        $statement = $database->prepare(<<<'SQL'
            SELECT r.*, e.title, e.project, e.starts_at, e.ends_at, e.capacity, e.format, e.contact_name, e.contact_email
            FROM sufw_booking_registrations r JOIN sufw_booking_events e ON e.id = r.event_id
            WHERE r.confirmation_token_hash = :tokenHash FOR UPDATE
            SQL);
        $statement->execute(['tokenHash' => hash('sha256', $token)]);
        $registration = $statement->fetch();
        if (!$registration || $registration['status'] !== 'pending_confirmation') throw new OutOfBoundsException('Dieser Bestätigungslink ist nicht mehr gültig.');
        if (strtotime($registration['confirmation_expires_at'].' UTC') < time()) {
            $database->prepare("UPDATE sufw_booking_registrations SET status = 'expired' WHERE id = :id")->execute(['id' => $registration['id']]);
            $database->commit();
            throw new OutOfBoundsException('Die Bestätigungsfrist ist abgelaufen. Bitte fragen Sie den Termin erneut an.');
        }
        $count = $database->prepare("SELECT COUNT(*) FROM sufw_booking_registrations WHERE event_id = :eventId AND status = 'confirmed'");
        $count->execute(['eventId' => $registration['event_id']]);
        if ((int) $count->fetchColumn() >= (int) $registration['capacity']) throw new RuntimeException('Der Termin wurde inzwischen vergeben. Bitte wählen Sie einen anderen Termin.');
        $database->prepare("UPDATE sufw_booking_registrations SET status = 'confirmed', confirmed_at = UTC_TIMESTAMP(), confirmation_token_hash = NULL WHERE id = :id")->execute(['id' => $registration['id']]);
        $history = $database->prepare(<<<'SQL'
            SELECT e.title, e.starts_at FROM sufw_booking_registrations r JOIN sufw_booking_events e ON e.id = r.event_id
            WHERE r.email = :email AND r.name = :name AND r.status = 'confirmed' ORDER BY e.starts_at
            SQL);
        $history->execute(['email' => $registration['email'], 'name' => $registration['name']]);
        $appointments = implode("\n", array_map(static fn (array $row): string => "- {$row['title']} am {$row['starts_at']}", $history->fetchAll()));
        $body = "Guten Tag {$registration['name']},\n\nIhr Termin ist bestätigt:\n{$registration['title']} am {$registration['starts_at']} bis {$registration['ends_at']}.\n\nIhre weiteren bestätigten Termine:\n$appointments\n\nBei Stornierungswunsch wenden Sie sich an {$registration['contact_name']} ({$registration['contact_email']}).";
        $database->commit();
        bookingSendMail($registration['email'], 'Ihr Termin ist bestätigt', $body, bookingIcsCalendar($registration));
        return $registration;
    } catch (Throwable $exception) {
        if ($database->inTransaction()) $database->rollBack();
        throw $exception;
    }
}

function bookingIcsEscape(string $value): string
{
    return str_replace(["\\", ";", ",", "\n"], ["\\\\", "\\;", "\\,", "\\n"], $value);
}