<?php
require_once __DIR__ . '/../config.php';

/**
 * Read JSON file and return decoded data
 */
function readJsonFile($file) {
    if (!file_exists($file)) {
        return [];
    }
    $content = file_get_contents($file);
    if (empty($content)) {
        return [];
    }
    $data = json_decode($content, true);
    return $data ? $data : [];
}

/**
 * Write data to JSON file
 */
function writeJsonFile($file, $data) {
    $dir = dirname($file);
    if (!is_dir($dir)) {
        mkdir($dir, 0755, true);
    }
    file_put_contents($file, json_encode($data, JSON_PRETTY_PRINT | JSON_UNESCAPED_UNICODE));
}

/**
 * Normalize admin username input.
 */
function normalizeAdminUsername($username) {
    return trim((string)$username);
}

/**
 * Normalize admin description input.
 */
function normalizeAdminDescription($description) {
    return trim((string)$description);
}

/**
 * Normalize admin email input.
 */
function normalizeAdminEmail($email) {
    return strtolower(trim((string)$email));
}

/**
 * Validate admin username format.
 */
function isValidAdminUsername($username) {
    $username = normalizeAdminUsername($username);
    return preg_match('/^[A-Za-z0-9][A-Za-z0-9._-]{2,49}$/', $username) === 1;
}

/**
 * Validate admin description.
 */
function isValidAdminDescription($description) {
    $description = normalizeAdminDescription($description);
    if ($description === '') {
        return false;
    }

    $length = function_exists('mb_strlen') ? mb_strlen($description) : strlen($description);
    return $length <= 120;
}

/**
 * Validate admin email.
 */
function isValidAdminEmail($email) {
    $email = normalizeAdminEmail($email);
    return $email !== '' && filter_var($email, FILTER_VALIDATE_EMAIL) !== false;
}

/**
 * Get default description for an admin account.
 */
function getDefaultAdminDescription($username) {
    return 'Admin';
}

/**
 * Get fallback admin email address from config.
 */
function getDefaultAdminEmail() {
    if (!defined('ADMIN_EMAIL') || !is_string(ADMIN_EMAIL)) {
        return '';
    }

    $fallbackEmail = normalizeAdminEmail(ADMIN_EMAIL);
    if (!isValidAdminEmail($fallbackEmail)) {
        return '';
    }

    return $fallbackEmail;
}

/**
 * Get full admin account records from JSON store.
 */
function getAdminAccounts() {
    $data = readJsonFile(ADMINS_FILE);
    $accounts = [];

    if (isset($data['admins']) && is_array($data['admins'])) {
        foreach ($data['admins'] as $username => $record) {
            $normalizedUsername = normalizeAdminUsername($username);
            if ($normalizedUsername === '') {
                continue;
            }

            $hash = '';
            $description = '';
            $email = getDefaultAdminEmail();
            if (is_string($record)) {
                $hash = $record;
                $description = getDefaultAdminDescription($normalizedUsername);
            } elseif (is_array($record)) {
                $hash = isset($record['password_hash']) && is_string($record['password_hash']) ? $record['password_hash'] : '';
                $description = isset($record['description']) ? normalizeAdminDescription($record['description']) : getDefaultAdminDescription($normalizedUsername);
                $email = isset($record['email']) ? normalizeAdminEmail($record['email']) : getDefaultAdminEmail();
            }

            if ($hash === '') {
                continue;
            }
            if (!isValidAdminDescription($description)) {
                $description = getDefaultAdminDescription($normalizedUsername);
            }
            if (!isValidAdminEmail($email)) {
                $email = getDefaultAdminEmail();
            }

            $accounts[$normalizedUsername] = [
                'password_hash' => $hash,
                'description' => $description,
                'email' => $email
            ];
        }
    }

    return $accounts;
}

/**
 * Get admin users for authentication (username => password hash).
 */
function getAdminUsers() {
    $accounts = getAdminAccounts();
    $admins = [];

    foreach ($accounts as $username => $account) {
        if (!isset($account['password_hash']) || !is_string($account['password_hash']) || $account['password_hash'] === '') {
            continue;
        }
        $admins[$username] = $account['password_hash'];
    }

    return $admins;
}

/**
 * Save full admin accounts to JSON store.
 */
function saveAdminAccounts($accounts) {
    $sanitizedAccounts = [];

    foreach ($accounts as $username => $account) {
        $normalizedUsername = normalizeAdminUsername($username);
        if ($normalizedUsername === '' || !is_array($account)) {
            continue;
        }

        $hash = isset($account['password_hash']) && is_string($account['password_hash']) ? $account['password_hash'] : '';
        if ($hash === '') {
            continue;
        }

        $description = isset($account['description']) ? normalizeAdminDescription($account['description']) : getDefaultAdminDescription($normalizedUsername);
        if (!isValidAdminDescription($description)) {
            $description = getDefaultAdminDescription($normalizedUsername);
        }

        $email = isset($account['email']) ? normalizeAdminEmail($account['email']) : getDefaultAdminEmail();
        if (!isValidAdminEmail($email)) {
            $email = getDefaultAdminEmail();
        }

        $sanitizedAccounts[$normalizedUsername] = [
            'password_hash' => $hash,
            'description' => $description,
            'email' => $email
        ];
    }

    ksort($sanitizedAccounts);
    writeJsonFile(ADMINS_FILE, ['admins' => $sanitizedAccounts]);
}

/**
 * Save admin users to JSON store (username => password hash).
 */
function saveAdminUsers($admins) {
    $existingAccounts = getAdminAccounts();
    $normalizedAccounts = [];

    foreach ($admins as $username => $hash) {
        $normalizedUsername = normalizeAdminUsername($username);
        if ($normalizedUsername === '' || !is_string($hash) || $hash === '') {
            continue;
        }

        $description = isset($existingAccounts[$normalizedUsername]['description'])
            ? normalizeAdminDescription($existingAccounts[$normalizedUsername]['description'])
            : getDefaultAdminDescription($normalizedUsername);
        if (!isValidAdminDescription($description)) {
            $description = getDefaultAdminDescription($normalizedUsername);
        }

        $email = isset($existingAccounts[$normalizedUsername]['email'])
            ? normalizeAdminEmail($existingAccounts[$normalizedUsername]['email'])
            : getDefaultAdminEmail();
        if (!isValidAdminEmail($email)) {
            $email = getDefaultAdminEmail();
        }

        $normalizedAccounts[$normalizedUsername] = [
            'password_hash' => $hash,
            'description' => $description,
            'email' => $email
        ];
    }

    saveAdminAccounts($normalizedAccounts);
}

/**
 * Get all products
 */
function getProducts() {
    $data = readJsonFile(PRODUCTS_FILE);
    return isset($data['products']) ? $data['products'] : [];
}

/**
 * Get product by ID
 */
function getProductById($id) {
    $products = getProducts();
    foreach ($products as $product) {
        if ($product['id'] == $id) {
            return $product;
        }
    }
    return null;
}

/**
 * Save products
 */
function saveProducts($products) {
    $data = ['products' => $products];
    writeJsonFile(PRODUCTS_FILE, $data);
}

/**
 * Resolve FAQ file path and force storage inside DATA_DIR.
 */
function getFaqFilePath(): string {
    $dataDir = defined('DATA_DIR') && is_string(DATA_DIR) ? DATA_DIR : (dirname(__DIR__) . '/data/');
    $defaultPath = rtrim($dataDir, '/\\') . '/faq.json';

    if (!defined('FAQ_FILE') || !is_string(FAQ_FILE) || FAQ_FILE === '') {
        return $defaultPath;
    }

    $configuredPath = FAQ_FILE;
    $normalizedDataDir = str_replace('\\', '/', rtrim($dataDir, '/\\')) . '/';
    $normalizedConfigured = str_replace('\\', '/', $configuredPath);

    if (strpos($normalizedConfigured, $normalizedDataDir) !== 0) {
        return $defaultPath;
    }

    return $configuredPath;
}

/**
 * Get FAQ markdown content from JSON store.
 */
function getFaqContent(): string {
    $defaultContent = "# FAQ\n\nHier kann der FAQ-Inhalt im Admin-Bereich bearbeitet werden.";
    $data = readJsonFile(getFaqFilePath());
    if (!is_array($data)) {
        return $defaultContent;
    }

    if (!isset($data['content']) || !is_string($data['content'])) {
        return $defaultContent;
    }

    return $data['content'];
}

/**
 * Save FAQ markdown content to JSON store.
 */
function saveFaqContent(string $markdown): void {
    writeJsonFile(getFaqFilePath(), ['content' => (string) $markdown]);
}

/**
 * Render inline markdown safely (bold + italic).
 */
function renderFaqInlineMarkdown(string $text): string {
    $escaped = htmlspecialchars($text, ENT_QUOTES, 'UTF-8');

    // Apply markdown after escaping so raw HTML is never executed.
    $escaped = preg_replace('/\*\*(.+?)\*\*/s', '<strong>$1</strong>', $escaped);
    $escaped = preg_replace('/(?<!\*)\*(?!\s)(.+?)(?<!\s)\*(?!\*)/s', '<em>$1</em>', $escaped);

    return $escaped;
}

/**
 * Render a minimal safe markdown subset for FAQ content.
 */
function renderFaqMarkdown(string $markdown): string {
    $normalized = str_replace(["\r\n", "\r"], "\n", $markdown);
    $lines = explode("\n", $normalized);
    $htmlParts = [];
    $paragraphLines = [];
    $listType = '';

    $flushParagraph = function () use (&$paragraphLines, &$htmlParts): void {
        if (empty($paragraphLines)) {
            return;
        }

        $renderedLines = [];
        foreach ($paragraphLines as $line) {
            $renderedLines[] = renderFaqInlineMarkdown($line);
        }

        $htmlParts[] = '<p>' . implode("<br>\n", $renderedLines) . '</p>';
        $paragraphLines = [];
    };

    $closeList = function () use (&$listType, &$htmlParts): void {
        if ($listType === '') {
            return;
        }

        $htmlParts[] = '</' . $listType . '>';
        $listType = '';
    };

    foreach ($lines as $line) {
        $line = rtrim($line);
        $trimmed = trim($line);

        if ($trimmed === '') {
            $flushParagraph();
            $closeList();
            continue;
        }

        if (preg_match('/^(#{1,3})\s+(.+)$/', $trimmed, $matches) === 1) {
            $flushParagraph();
            $closeList();
            $level = strlen($matches[1]);
            $htmlParts[] = '<h' . $level . '>' . renderFaqInlineMarkdown($matches[2]) . '</h' . $level . '>';
            continue;
        }

        if (preg_match('/^\s*[-*]\s+(.+)$/', $line, $matches) === 1) {
            $flushParagraph();
            if ($listType !== 'ul') {
                $closeList();
                $listType = 'ul';
                $htmlParts[] = '<ul>';
            }
            $htmlParts[] = '<li>' . renderFaqInlineMarkdown($matches[1]) . '</li>';
            continue;
        }

        if (preg_match('/^\s*\d+\.\s+(.+)$/', $line, $matches) === 1) {
            $flushParagraph();
            if ($listType !== 'ol') {
                $closeList();
                $listType = 'ol';
                $htmlParts[] = '<ol>';
            }
            $htmlParts[] = '<li>' . renderFaqInlineMarkdown($matches[1]) . '</li>';
            continue;
        }

        $closeList();
        $paragraphLines[] = $trimmed;
    }

    $flushParagraph();
    $closeList();

    if (empty($htmlParts)) {
        return '<p>Keine FAQ-Inhalte vorhanden.</p>';
    }

    return implode("\n", $htmlParts);
}

/**
 * Get all reservations
 */
function getReservations() {
    $data = readJsonFile(RESERVATIONS_FILE);
    return isset($data['reservations']) ? $data['reservations'] : [];
}

/**
 * Get reservation by order number
 */
function getReservationByOrderNumber($orderNumber) {
    $reservations = getReservations();
    foreach ($reservations as $reservation) {
        if (isset($reservation['id']) && $reservation['id'] === $orderNumber && !isReservationHidden($reservation)) {
            return $reservation;
        }
    }
    return null;
}

/**
 * Get remembered order IDs for the current browser profile.
 */
function getRememberedOrderIds(): array {
    return readSignedOrderHistoryCookie();
}

/**
 * Remember a newly created order ID in browser history cookie.
 */
function rememberOrderId(string $orderId): void {
    if (!isValidOrderHistoryOrderId($orderId)) {
        return;
    }

    $existingIds = getRememberedOrderIds();
    $updatedIds = [$orderId];

    foreach ($existingIds as $existingId) {
        if ($existingId !== $orderId) {
            $updatedIds[] = $existingId;
        }
    }

    $maxIds = getOrderHistoryMaxIds();
    if (count($updatedIds) > $maxIds) {
        $updatedIds = array_slice($updatedIds, 0, $maxIds);
    }

    writeSignedOrderHistoryCookie($updatedIds);
}

/**
 * Read and validate signed browser order history cookie.
 */
function readSignedOrderHistoryCookie(): array {
    $cookieName = getOrderHistoryCookieName();
    if (!isset($_COOKIE[$cookieName]) || !is_string($_COOKIE[$cookieName])) {
        return [];
    }

    $secret = getOrderHistorySecret();
    if ($secret === '') {
        return [];
    }

    $cookieValue = $_COOKIE[$cookieName];
    $parts = explode('.', $cookieValue, 2);
    if (count($parts) !== 2) {
        return [];
    }

    $encodedPayload = $parts[0];
    $signature = $parts[1];
    if ($encodedPayload === '' || $signature === '') {
        return [];
    }

    $expectedSignature = hash_hmac('sha256', $encodedPayload, $secret);
    if (!hash_equals($expectedSignature, $signature)) {
        return [];
    }

    $payloadJson = base64UrlDecode($encodedPayload);
    if ($payloadJson === null) {
        return [];
    }

    $payload = json_decode($payloadJson, true);
    if (!is_array($payload)) {
        return [];
    }

    $version = isset($payload['v']) ? (int)$payload['v'] : 0;
    if ($version !== 1) {
        return [];
    }

    $ids = isset($payload['ids']) && is_array($payload['ids']) ? $payload['ids'] : [];
    return sanitizeOrderHistoryIds($ids);
}

/**
 * Write signed browser order history cookie.
 */
function writeSignedOrderHistoryCookie(array $ids): void {
    if (headers_sent()) {
        return;
    }

    $secret = getOrderHistorySecret();
    if ($secret === '') {
        return;
    }

    $sanitizedIds = sanitizeOrderHistoryIds($ids);
    $payload = [
        'v' => 1,
        'ids' => $sanitizedIds,
        'iat' => time()
    ];

    $payloadJson = json_encode($payload, JSON_UNESCAPED_UNICODE);
    if ($payloadJson === false) {
        return;
    }

    $encodedPayload = base64UrlEncode($payloadJson);
    $signature = hash_hmac('sha256', $encodedPayload, $secret);
    $cookieValue = $encodedPayload . '.' . $signature;

    $expires = time() + (getOrderHistoryTtlDays() * 86400);
    $success = setcookie(getOrderHistoryCookieName(), $cookieValue, [
        'expires' => $expires,
        'path' => getOrderHistoryCookiePath(),
        'secure' => isHttpsRequest(),
        'httponly' => true,
        'samesite' => 'Lax'
    ]);

    if ($success) {
        $_COOKIE[getOrderHistoryCookieName()] = $cookieValue;
    }
}

/**
 * Build a safe, deduplicated order history ID list.
 */
function sanitizeOrderHistoryIds(array $ids): array {
    $result = [];
    $seen = [];
    $maxIds = getOrderHistoryMaxIds();

    foreach ($ids as $id) {
        if (!is_string($id) || !isValidOrderHistoryOrderId($id)) {
            continue;
        }
        if (isset($seen[$id])) {
            continue;
        }
        $seen[$id] = true;
        $result[] = $id;

        if (count($result) >= $maxIds) {
            break;
        }
    }

    return $result;
}

/**
 * Check if order ID matches configured pattern.
 */
function isValidOrderHistoryOrderId($orderId): bool {
    if (!is_string($orderId) || $orderId === '') {
        return false;
    }

    $prefix = defined('ORDER_PREFIX') ? ORDER_PREFIX : 'ORD';
    $pattern = '/^' . preg_quote($prefix, '/') . '-\d{4}-\d+$/';
    return preg_match($pattern, $orderId) === 1;
}

/**
 * Base64url encode helper.
 */
function base64UrlEncode(string $data): string {
    return rtrim(strtr(base64_encode($data), '+/', '-_'), '=');
}

/**
 * Base64url decode helper.
 */
function base64UrlDecode(string $data): ?string {
    $remainder = strlen($data) % 4;
    if ($remainder > 0) {
        $data .= str_repeat('=', 4 - $remainder);
    }

    $decoded = base64_decode(strtr($data, '-_', '+/'), true);
    if ($decoded === false) {
        return null;
    }
    return $decoded;
}

/**
 * Get cookie name for order history.
 */
function getOrderHistoryCookieName(): string {
    return defined('ORDER_HISTORY_COOKIE_NAME') ? ORDER_HISTORY_COOKIE_NAME : 'order_history';
}

/**
 * Get secret for order history cookie signing.
 */
function getOrderHistorySecret(): string {
    return defined('ORDER_HISTORY_COOKIE_SECRET') ? (string) ORDER_HISTORY_COOKIE_SECRET : '';
}

/**
 * Get maximum number of remembered order IDs.
 */
function getOrderHistoryMaxIds(): int {
    $maxIds = defined('ORDER_HISTORY_MAX_IDS') ? (int) ORDER_HISTORY_MAX_IDS : 10;
    return $maxIds > 0 ? $maxIds : 10;
}

/**
 * Get order history cookie retention days.
 */
function getOrderHistoryTtlDays(): int {
    $ttlDays = defined('ORDER_HISTORY_COOKIE_TTL_DAYS') ? (int) ORDER_HISTORY_COOKIE_TTL_DAYS : 365;
    return $ttlDays > 0 ? $ttlDays : 365;
}

/**
 * Get cookie path from SITE_URL.
 */
function getOrderHistoryCookiePath(): string {
    $siteUrl = defined('SITE_URL') ? trim((string) SITE_URL) : '';
    if (strpos($siteUrl, '://') !== false) {
        $parsedPath = parse_url($siteUrl, PHP_URL_PATH);
        $siteUrl = is_string($parsedPath) ? $parsedPath : '';
    }

    if ($siteUrl === '' || $siteUrl === '/') {
        return '/';
    }

    if ($siteUrl[0] !== '/') {
        $siteUrl = '/' . $siteUrl;
    }

    return rtrim($siteUrl, '/');
}

/**
 * Detect whether current request uses HTTPS.
 */
function isHttpsRequest(): bool {
    if (!empty($_SERVER['HTTPS']) && strtolower((string) $_SERVER['HTTPS']) !== 'off') {
        return true;
    }
    if (isset($_SERVER['SERVER_PORT']) && (int) $_SERVER['SERVER_PORT'] === 443) {
        return true;
    }
    if (!empty($_SERVER['HTTP_X_FORWARDED_PROTO']) && strtolower((string) $_SERVER['HTTP_X_FORWARDED_PROTO']) === 'https') {
        return true;
    }
    return false;
}

/**
 * Check if reservation is hidden (spam/deleted)
 */
function isReservationHidden($reservation) {
    return isset($reservation['is_hidden']) && $reservation['is_hidden'] === true;
}

/**
 * Save reservations
 */
function saveReservations($reservations) {
    $data = ['reservations' => $reservations];
    writeJsonFile(RESERVATIONS_FILE, $data);
}

/**
 * Generate order number
 * Pattern: PREFIX-YEAR-SEQ
 */
function generateReservationId() {
    $reservations = getReservations();
    $year = date('Y');
    $prefix = defined('ORDER_PREFIX') ? ORDER_PREFIX : 'ORD';
    $max = 0;
    $pattern = '/^' . preg_quote($prefix, '/') . '-\\d{4}-(\\d+)$/';

    foreach ($reservations as $reservation) {
        if (!isset($reservation['id'])) {
            continue;
        }
        if (preg_match($pattern, $reservation['id'], $matches)) {
            $num = (int)$matches[1];
            if ($num > $max) {
                $max = $num;
            }
        }
    }

    $next = $max + 1;
    return sprintf('%s-%s-%03d', $prefix, $year, $next);
}

/**
 * Check if product has enough stock
 * For apparel: checks stock for specific size
 * For merch: checks general stock
 */
function checkStock($productId, $quantity, $size = null) {
    $product = getProductById($productId);
    if (!$product) {
        return false;
    }
    
    // For apparel with sizes, check stock per size
    if ($product['category'] === 'apparel' && !empty($product['sizes']) && $size !== null) {
        if (!isset($product['stock_by_size']) || !is_array($product['stock_by_size'])) {
            return false;
        }
        $sizeStock = isset($product['stock_by_size'][$size]) ? (int)$product['stock_by_size'][$size] : 0;
        return $sizeStock >= $quantity;
    }
    
    // For merch or apparel without size-specific stock, use general stock
    $stock = isset($product['stock']) ? (int)$product['stock'] : 0;
    return $stock >= $quantity;
}

/**
 * Get stock for a product (per size for apparel, general for merch)
 */
function getStock($product, $size = null) {
    if ($product['category'] === 'apparel' && !empty($product['sizes']) && $size !== null) {
        if (isset($product['stock_by_size']) && is_array($product['stock_by_size'])) {
            return isset($product['stock_by_size'][$size]) ? (int)$product['stock_by_size'][$size] : 0;
        }
    }
    return isset($product['stock']) ? (int)$product['stock'] : 0;
}

/**
 * Get total stock for a product (sum of all sizes for apparel)
 */
function getTotalStock($product) {
    if ($product['category'] === 'apparel' && isset($product['stock_by_size']) && is_array($product['stock_by_size'])) {
        return array_sum($product['stock_by_size']);
    }
    return isset($product['stock']) ? (int)$product['stock'] : 0;
}

/**
 * Allocate stock for reservation
 */
function allocateStock($productId, $quantity, $size = null) {
    $products = getProducts();
    foreach ($products as &$product) {
        if ($product['id'] == $productId) {
            // For apparel with sizes, allocate per size
            if ($product['category'] === 'apparel' && !empty($product['sizes']) && $size !== null) {
                if (!isset($product['stock_by_size']) || !is_array($product['stock_by_size'])) {
                    $product['stock_by_size'] = [];
                }
                if (!isset($product['stock_by_size'][$size])) {
                    $product['stock_by_size'][$size] = 0;
                }
                $product['stock_by_size'][$size] -= $quantity;
                if ($product['stock_by_size'][$size] < 0) {
                    $product['stock_by_size'][$size] = 0;
                }
            } else {
                // For merch or general stock
                if (!isset($product['stock'])) {
                    $product['stock'] = 0;
                }
                $product['stock'] -= $quantity;
                if ($product['stock'] < 0) {
                    $product['stock'] = 0;
                }
            }
            break;
        }
    }
    saveProducts($products);
}

/**
 * Release stock from reservation
 */
function releaseStock($productId, $quantity, $size = null) {
    $products = getProducts();
    foreach ($products as &$product) {
        if ($product['id'] == $productId) {
            // For apparel with sizes, release per size
            if ($product['category'] === 'apparel' && !empty($product['sizes']) && $size !== null) {
                if (!isset($product['stock_by_size']) || !is_array($product['stock_by_size'])) {
                    $product['stock_by_size'] = [];
                }
                if (!isset($product['stock_by_size'][$size])) {
                    $product['stock_by_size'][$size] = 0;
                }
                $product['stock_by_size'][$size] += $quantity;
            } else {
                // For merch or general stock
                if (!isset($product['stock'])) {
                    $product['stock'] = 0;
                }
                $product['stock'] += $quantity;
            }
            break;
        }
    }
    saveProducts($products);
}

/**
 * Create new reservation
 */
function createReservation($customerName, $customerEmail, $items) {
    $reservations = getReservations();
    
    // Validate stock for all items
    foreach ($items as $item) {
        $size = isset($item['size']) ? $item['size'] : null;
        if (!checkStock($item['product_id'], $item['quantity'], $size)) {
            $product = getProductById($item['product_id']);
            $productName = $product ? $product['name'] : 'Produkt';
            $sizeInfo = $size ? " (Größe: $size)" : '';
            return ['success' => false, 'message' => "Nicht genügend Lagerbestand für: $productName$sizeInfo"];
        }
    }
    
    // Allocate stock
    foreach ($items as $item) {
        $size = isset($item['size']) ? $item['size'] : null;
        allocateStock($item['product_id'], $item['quantity'], $size);
    }
    
    // Create reservation
    $now = new DateTime();
    $expires = clone $now;
    $expires->modify('+' . RESERVATION_EXPIRY_DAYS . ' days');
    
    $reservation = [
        'id' => generateReservationId(),
        'customer_name' => $customerName,
        'customer_email' => $customerEmail,
        'items' => $items,
        'created' => $now->format('Y-m-d H:i:s'),
        'expires' => $expires->format('Y-m-d H:i:s'),
        'status' => 'open',
        'picked_up' => false,
        'type' => 'regular',
        'is_hidden' => false
    ];
    
    $reservations[] = $reservation;
    saveReservations($reservations);
    
    // Send confirmation emails
    sendReservationEmails($reservation);
    
    return ['success' => true, 'reservation' => $reservation];
}

/**
 * Create new backorder reservation
 */
function createBackorderReservation($customerName, $customerEmail, $items) {
    $reservations = getReservations();
    
    $now = new DateTime();
    
    $reservation = [
        'id' => generateReservationId(),
        'customer_name' => $customerName,
        'customer_email' => $customerEmail,
        'items' => $items,
        'created' => $now->format('Y-m-d H:i:s'),
        'expires' => '',
        'status' => 'open',
        'picked_up' => false,
        'type' => 'backorder',
        'backorder_status' => 'pending',
        'is_hidden' => false
    ];
    
    $reservations[] = $reservation;
    saveReservations($reservations);
    
    // Send confirmation emails
    sendBackorderEmails($reservation);
    
    return ['success' => true, 'reservation' => $reservation];
}

/**
 * Mark reservation as picked up
 */
function markReservationPickedUp($reservationId) {
    $reservations = getReservations();
    foreach ($reservations as &$reservation) {
        if ($reservation['id'] === $reservationId) {
            if (isReservationHidden($reservation)) {
                break;
            }
            $reservation['picked_up'] = true;
            $reservation['status'] = 'picked_up';
            break;
        }
    }
    saveReservations($reservations);
}

/**
 * Mark reservation/backorder as spam/deleted and hide it from non-admin views.
 * For open regular reservations we release stock, because the order is discarded.
 */
function markReservationHidden($reservationId) {
    $reservations = getReservations();
    foreach ($reservations as &$reservation) {
        if ($reservation['id'] !== $reservationId) {
            continue;
        }
        if (isReservationHidden($reservation)) {
            return ['success' => false, 'message' => 'Bestellung ist bereits als Spam/Gelöscht markiert.'];
        }

        $isBackorder = isset($reservation['type']) && $reservation['type'] === 'backorder';
        if (!$isBackorder && isset($reservation['status']) && $reservation['status'] === 'open' && empty($reservation['picked_up'])) {
            foreach ($reservation['items'] as $item) {
                $size = isset($item['size']) ? $item['size'] : null;
                releaseStock($item['product_id'], $item['quantity'], $size);
            }
            $reservation['status'] = 'deleted';
        }

        $reservation['is_hidden'] = true;
        $reservation['hidden_at'] = date('Y-m-d H:i:s');
        $reservation['hidden_reason'] = 'spam_deleted';
        saveReservations($reservations);

        return ['success' => true];
    }

    return ['success' => false, 'message' => 'Bestellung nicht gefunden.'];
}

/**
 * Check and expire old reservations
 */
function expireOldReservations() {
    $reservations = getReservations();
    $now = new DateTime();
    $changed = false;
    
    foreach ($reservations as &$reservation) {
        if (isReservationHidden($reservation)) {
            continue;
        }
        if ($reservation['status'] === 'open' && !$reservation['picked_up']) {
            if (isset($reservation['type']) && $reservation['type'] === 'backorder') {
                continue;
            }
            if (empty($reservation['expires'])) {
                continue;
            }
            $expires = new DateTime($reservation['expires']);
            if ($now > $expires) {
                $reservation['status'] = 'expired';
                // Release stock
                foreach ($reservation['items'] as $item) {
                    $size = isset($item['size']) ? $item['size'] : null;
                    releaseStock($item['product_id'], $item['quantity'], $size);
                }
                $changed = true;
            }
        }
    }
    
    if ($changed) {
        saveReservations($reservations);
    }
}

/**
 * Check if all items are in stock
 */
function canFulfillReservationItems($items) {
    foreach ($items as $item) {
        $size = isset($item['size']) ? $item['size'] : null;
        if (!checkStock($item['product_id'], $item['quantity'], $size)) {
            return false;
        }
    }
    return true;
}

/**
 * Mark backorder as available
 */
function markBackorderAvailable($reservationId) {
    $reservations = getReservations();
    foreach ($reservations as &$reservation) {
        if ($reservation['id'] === $reservationId) {
            if (isReservationHidden($reservation)) {
                return ['success' => false, 'message' => 'Diese Vorbestellung ist als Spam/Gelöscht markiert.'];
            }
            if (!isset($reservation['type']) || $reservation['type'] !== 'backorder') {
                return ['success' => false, 'message' => 'Diese Vorbestellung wurde bereits in eine Bestellung umgewandelt.'];
            }
            if (isset($reservation['backorder_status']) && $reservation['backorder_status'] === 'notified') {
                return ['success' => false, 'message' => 'Diese Vorbestellung wurde bereits informiert.'];
            }
            if (!canFulfillReservationItems($reservation['items'])) {
                return ['success' => false, 'message' => 'Nicht alle Artikel sind verfügbar.'];
            }
            
            foreach ($reservation['items'] as $item) {
                $size = isset($item['size']) ? $item['size'] : null;
                allocateStock($item['product_id'], $item['quantity'], $size);
            }

            $now = new DateTime();
            $expires = clone $now;
            $expires->modify('+' . RESERVATION_EXPIRY_DAYS . ' days');

            $reservation['type'] = 'regular';
            $reservation['status'] = 'open';
            $reservation['picked_up'] = false;
            $reservation['expires'] = $expires->format('Y-m-d H:i:s');
            if (isset($reservation['backorder_status'])) {
                unset($reservation['backorder_status']);
            }
            saveReservations($reservations);
            
            sendBackorderAvailableEmail($reservation);
            
            return ['success' => true, 'reservation' => $reservation];
        }
    }
    return ['success' => false, 'message' => 'Vorbestellung nicht gefunden.'];
}

/**
 * Sanitize input
 */
function sanitize($input) {
    return htmlspecialchars(strip_tags(trim($input)), ENT_QUOTES, 'UTF-8');
}

/**
 * Format price
 */
function formatPrice($price) {
    return number_format($price, 2, ',', '.') . ' €';
}

/**
 * Format date
 */
function formatDate($dateString) {
    $date = new DateTime($dateString);
    return $date->format('d.m.Y H:i');
}

/**
 * Send email
 */
function sendEmail($to, $subject, $message, $isHtml = true) {
    $headers = [];
    $headers[] = 'From: ' . FROM_NAME . ' <' . FROM_EMAIL . '>';
    $headers[] = 'Reply-To: ' . FROM_EMAIL;
    $headers[] = 'X-Mailer: PHP/' . phpversion();
    
    if ($isHtml) {
        $headers[] = 'MIME-Version: 1.0';
        $headers[] = 'Content-type: text/html; charset=UTF-8';
    }
    
    return mail($to, $subject, $message, implode("\r\n", $headers));
}

/**
 * Get all admin notification recipients from admin accounts.
 * Falls back to ADMIN_EMAIL if no account email is configured.
 */
function getAdminNotificationEmails() {
    $accounts = getAdminAccounts();
    $emails = [];

    foreach ($accounts as $account) {
        if (!isset($account['email'])) {
            continue;
        }

        $email = normalizeAdminEmail($account['email']);
        if (!isValidAdminEmail($email)) {
            continue;
        }
        $emails[] = $email;
    }

    if (empty($emails)) {
        $fallbackEmail = getDefaultAdminEmail();
        if ($fallbackEmail !== '') {
            $emails[] = $fallbackEmail;
        }
    }

    return array_values(array_unique($emails));
}

/**
 * Send admin notifications to all configured recipients.
 */
function sendAdminNotificationEmails($subject, $message, $isHtml = true) {
    $emails = getAdminNotificationEmails();

    if (empty($emails)) {
        return false;
    }

    $sent = false;
    foreach ($emails as $email) {
        $result = sendEmail($email, $subject, $message, $isHtml);
        if ($result) {
            $sent = true;
        }
    }

    return $sent;
}

/**
 * Send reservation confirmation emails
 */
function sendReservationEmails($reservation) {
    $products = getProducts();
    
    // Build items list
    $itemsHtml = '<ul style="list-style: none; margin: 0; padding: 0;">';
    foreach ($reservation['items'] as $item) {
        $product = getProductById($item['product_id']);
        if ($product) {
            $sizeInfo = '';
            if (isset($item['size']) && !empty($item['size'])) {
                $sizeInfo = ' - Größe: ' . htmlspecialchars($item['size']);
            }
            $itemsHtml .= '<li style="margin: 0 0 0.6rem 0; padding: 0.75rem 0.9rem; background: #28292a; border: 1px solid #4a5263; border-radius: 6px;"><strong style="color: #cac300;">' . htmlspecialchars($product['name']) . '</strong>' . $sizeInfo . ' - Menge: <strong>' . (int) $item['quantity'] . '</strong></li>';
        }
    }
    $itemsHtml .= '</ul>';
    
    // Customer email
    $customerSubject = 'Ihre Reservierung bei ' . SITE_NAME;
    $customerMessage = '
    <html>
    <head>
        <meta charset="UTF-8">
    </head>
    <body style="font-family: Arial, sans-serif; line-height: 1.6; color: #f5f7fb; background: #28292a; padding: 1.5rem;">
        <div style="max-width: 640px; margin: 0 auto; background: #2f3541; padding: 1.5rem 2rem; border-radius: 10px; border: 1px solid #3b4252;">
            <h2 style="color: #cac300; margin-top: 0;">Reservierung bestätigt</h2>
            <p>Sehr geehrte/r ' . htmlspecialchars($reservation['customer_name']) . ',</p>
            <p>vielen Dank für Ihre Reservierung bei ' . SITE_NAME . '.</p>
            
            <div style="background: #28292a; border: 2px solid #cac300; padding: 1.5rem; margin: 1.5rem 0; border-radius: 8px; text-align: center;">
                <h3 style="margin-top: 0; color: #f5f7fb;">Ihre Bestellnummer:</h3>
                <p style="margin: 0; color: #cac300; font-family: monospace;">' . htmlspecialchars($reservation['id']) . '</p>
            </div>
            
            <h3>Reservierungsdetails:</h3>
            <p><strong>Bestellnummer:</strong> ' . htmlspecialchars($reservation['id']) . '</p>
            <p><strong>Erstellt am:</strong> ' . formatDate($reservation['created']) . '</p>
            <p><strong>Gültig bis:</strong> ' . formatDate($reservation['expires']) . '</p>
            
            <h3>Reservierte Artikel:</h3>
            <div style="background: #303745; border: 1px solid #4a5263; border-left: 4px solid #cac300; border-radius: 8px; padding: 1rem;">' . $itemsHtml . '</div>
            
            <p><strong>Wichtig:</strong> Bitte nennen Sie diese Bestellnummer bei der Abholung. Die Reservierung ist bis zum ' . formatDate($reservation['expires']) . ' gültig.</p>
            
            <p>Mit freundlichen Grüßen<br>' . SITE_NAME . '</p>
        </div>
    </body>
    </html>';
    
    sendEmail($reservation['customer_email'], $customerSubject, $customerMessage);
    
    // Admin email
    $adminSubject = 'Neue Reservierung: ' . $reservation['id'];
    $adminMessage = '
    <html>
    <head>
        <meta charset="UTF-8">
    </head>
    <body style="font-family: Arial, sans-serif; line-height: 1.6; color: #f5f7fb; background: #28292a; padding: 1.5rem;">
        <div style="max-width: 640px; margin: 0 auto; background: #2f3541; padding: 1.5rem 2rem; border-radius: 10px; border: 1px solid #3b4252;">
            <h2 style="color: #cac300; margin-top: 0;">Neue Reservierung</h2>
            <p>Eine neue Reservierung wurde erstellt:</p>
            
            <div style="background: #28292a; border: 2px solid #cac300; padding: 1.5rem; margin: 1.5rem 0; border-radius: 8px;">
                <h3 style="margin-top: 0;">Bestellnummer:</h3>
                <p style="margin: 0; color: #cac300; font-family: monospace;">' . htmlspecialchars($reservation['id']) . '</p>
            </div>
            
            <h3>Kundendaten:</h3>
            <p><strong>Name:</strong> ' . htmlspecialchars($reservation['customer_name']) . '</p>
            <p><strong>E-Mail:</strong> ' . htmlspecialchars($reservation['customer_email']) . '</p>
            
            <h3>Reservierungsdetails:</h3>
            <p><strong>Bestellnummer:</strong> ' . htmlspecialchars($reservation['id']) . '</p>
            <p><strong>Erstellt am:</strong> ' . formatDate($reservation['created']) . '</p>
            <p><strong>Gültig bis:</strong> ' . formatDate($reservation['expires']) . '</p>
            
            <h3>Reservierte Artikel:</h3>
            <div style="background: #303745; border: 1px solid #4a5263; border-left: 4px solid #cac300; border-radius: 8px; padding: 1rem;">' . $itemsHtml . '</div>
        </div>
    </body>
    </html>';
    
    sendAdminNotificationEmails($adminSubject, $adminMessage);
}

/**
 * Send backorder confirmation emails
 */
function sendBackorderEmails($reservation) {
    // Build items list
    $itemsHtml = '<ul style="list-style: none; margin: 0; padding: 0;">';
    foreach ($reservation['items'] as $item) {
        $product = getProductById($item['product_id']);
        if ($product) {
            $sizeInfo = '';
            if (isset($item['size']) && !empty($item['size'])) {
                $sizeInfo = ' - Größe: ' . htmlspecialchars($item['size']);
            }
            $itemsHtml .= '<li style="margin: 0 0 0.6rem 0; padding: 0.75rem 0.9rem; background: #28292a; border: 1px solid #4a5263; border-radius: 6px;"><strong style="color: #cac300;">' . htmlspecialchars($product['name']) . '</strong>' . $sizeInfo . ' - Menge: <strong>' . (int) $item['quantity'] . '</strong></li>';
        }
    }
    $itemsHtml .= '</ul>';
    
    // Customer email
    $customerSubject = 'Vorbestellung bei ' . SITE_NAME;
    $customerMessage = '
    <html>
    <head>
        <meta charset="UTF-8">
    </head>
    <body style="font-family: Arial, sans-serif; line-height: 1.6; color: #f5f7fb; background: #28292a; padding: 1.5rem;">
        <div style="max-width: 640px; margin: 0 auto; background: #2f3541; padding: 1.5rem 2rem; border-radius: 10px; border: 1px solid #3b4252;">
            <h2 style="color: #cac300; margin-top: 0;">Vorbestellung bestätigt</h2>
            <p>Sehr geehrte/r ' . htmlspecialchars($reservation['customer_name']) . ',</p>
            <p>vielen Dank für Ihre Vorbestellung bei ' . SITE_NAME . '.</p>
            
            <div style="background: #28292a; border: 2px solid #cac300; padding: 1.5rem; margin: 1.5rem 0; border-radius: 8px; text-align: center;">
                <h3 style="margin-top: 0; color: #f5f7fb;">Ihre Bestellnummer:</h3>
                <p style="margin: 0; color: #cac300; font-family: monospace;">' . htmlspecialchars($reservation['id']) . '</p>
            </div>
            
            <h3>Vorbestellungsdetails:</h3>
            <p><strong>Bestellnummer:</strong> ' . htmlspecialchars($reservation['id']) . '</p>
            <p><strong>Erstellt am:</strong> ' . formatDate($reservation['created']) . '</p>
            
            <h3>Vorbestellte Artikel:</h3>
            <div style="background: #303745; border: 1px solid #4a5263; border-left: 4px solid #cac300; border-radius: 8px; padding: 1rem;">' . $itemsHtml . '</div>
            
            <div style="background: #28292a; border: 2px solid #cf2e2e; padding: 1.5rem; margin: 1.5rem 0; border-radius: 8px;">
                <strong>Hinweis:</strong> Die Lieferzeiten sind nicht bekannt, da die Bestellung in Chargen erfolgt.
            </div>
            
            <p>Wir informieren Sie, sobald die komplette Vorbestellung zur Abholung bereit ist.</p>
            
            <p>Mit freundlichen Grüßen<br>' . SITE_NAME . '</p>
        </div>
    </body>
    </html>';
    
    sendEmail($reservation['customer_email'], $customerSubject, $customerMessage);
    
    // Admin email
    $adminSubject = 'Neue Vorbestellung: ' . $reservation['id'];
    $adminMessage = '
    <html>
    <head>
        <meta charset="UTF-8">
    </head>
    <body style="font-family: Arial, sans-serif; line-height: 1.6; color: #f5f7fb; background: #28292a; padding: 1.5rem;">
        <div style="max-width: 640px; margin: 0 auto; background: #2f3541; padding: 1.5rem 2rem; border-radius: 10px; border: 1px solid #3b4252;">
            <h2 style="color: #cac300; margin-top: 0;">Neue Vorbestellung</h2>
            <p>Eine neue Vorbestellung wurde erstellt:</p>
            
            <div style="background: #28292a; border: 2px solid #cac300; padding: 1.5rem; margin: 1.5rem 0; border-radius: 8px;">
                <h3 style="margin-top: 0;">Bestellnummer:</h3>
                <p style="margin: 0; color: #cac300; font-family: monospace;">' . htmlspecialchars($reservation['id']) . '</p>
            </div>
            
            <h3>Kundendaten:</h3>
            <p><strong>Name:</strong> ' . htmlspecialchars($reservation['customer_name']) . '</p>
            <p><strong>E-Mail:</strong> ' . htmlspecialchars($reservation['customer_email']) . '</p>
            
            <h3>Vorbestellungsdetails:</h3>
            <p><strong>Bestellnummer:</strong> ' . htmlspecialchars($reservation['id']) . '</p>
            <p><strong>Erstellt am:</strong> ' . formatDate($reservation['created']) . '</p>
            
            <h3>Vorbestellte Artikel:</h3>
            <div style="background: #303745; border: 1px solid #4a5263; border-left: 4px solid #cac300; border-radius: 8px; padding: 1rem;">' . $itemsHtml . '</div>
        </div>
    </body>
    </html>';
    
    sendAdminNotificationEmails($adminSubject, $adminMessage);
}

/**
 * Send backorder availability email
 */
function sendBackorderAvailableEmail($reservation) {
    $itemsHtml = '<ul>';
    foreach ($reservation['items'] as $item) {
        $product = getProductById($item['product_id']);
        if ($product) {
            $sizeInfo = '';
            if (isset($item['size']) && !empty($item['size'])) {
                $sizeInfo = ' - Größe: ' . htmlspecialchars($item['size']);
            }
            $itemsHtml .= '<li>' . htmlspecialchars($product['name']) . $sizeInfo . ' - Menge: ' . $item['quantity'] . '</li>';
        }
    }
    $itemsHtml .= '</ul>';
    
    $subject = 'Ihre Vorbestellung ist zur Abholung bereit';
    $message = '
    <html>
    <head>
        <meta charset="UTF-8">
    </head>
    <body style="font-family: Arial, sans-serif; line-height: 1.6; color: #f5f7fb; background: #28292a; padding: 1.5rem;">
        <div style="max-width: 640px; margin: 0 auto; background: #2f3541; padding: 1.5rem 2rem; border-radius: 10px; border: 1px solid #3b4252;">
            <h2 style="color: #cac300; margin-top: 0;">Vorbestellung zur Abholung bereit</h2>
            <p>Sehr geehrte/r ' . htmlspecialchars($reservation['customer_name']) . ',</p>
            <p>Ihre komplette Vorbestellung ist jetzt zur Abholung bereit.</p>
            
            <div style="background: #28292a; border: 2px solid #cac300; padding: 1.5rem; margin: 1.5rem 0; border-radius: 8px; text-align: center;">
                <h3 style="margin-top: 0; color: #f5f7fb;">Ihre Bestellnummer:</h3>
                <h2 style="font-size: 2rem; letter-spacing: 0.2rem; color: #cac300; font-family: monospace;">' . htmlspecialchars($reservation['id']) . '</h2>
            </div>
            
            <h3>Bereitliegende Artikel:</h3>
            ' . $itemsHtml . '
            
            <p>Bitte nennen Sie die Bestellnummer bei der Abholung.</p>
            
            <p>Mit freundlichen Grüßen<br>' . SITE_NAME . '</p>
        </div>
    </body>
    </html>';
    
    sendEmail($reservation['customer_email'], $subject, $message);
}