<?php
/**
 * API: Lizenzverwaltung
 * GET  /api/licenses?class_id=X          → Lizenzen der Klasse (Lehrer)
 * GET  /api/licenses?admin=1             → Alle Lizenzen (Super-Admin)
 * POST /api/licenses {action}            → Lizenz einlösen/zuweisen/generieren
 */

$method = $_SERVER['REQUEST_METHOD'];
$db = Database::get();

// ─────────────────────────────────────────────────────────────────────
//  Vertriebs-Helfer (Chargen-Vergabe, Storno, Verlaengerung, Mail, Schutz)
// ─────────────────────────────────────────────────────────────────────
const LIC_TYPES = ['marktplatz', 'direktvertrieb', 'privat'];

/** Neuer Lizenzcode: 5×4 aus 32er-Alphabet (ohne I,O,0,1) = ~100 Bit Entropie. */
function lic_new_code(): string {
    $a = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789'; $n = strlen($a);
    $g = [];
    for ($i = 0; $i < 5; $i++) {
        $s = '';
        for ($k = 0; $k < 4; $k++) $s .= $a[random_int(0, $n - 1)];
        $g[] = $s;
    }
    return implode('-', $g); // XXXX-XXXX-XXXX-XXXX-XXXX (24 Zeichen)
}

/** Schuljahr-String "26/27" aus einem Datum (Schuljahr beginnt im August). */
function lic_school_year_from(?string $date): string {
    $ts = $date ? strtotime($date) : time();
    $y = (int)date('Y', $ts); $m = (int)date('n', $ts);
    $start = ($m >= 8) ? $y : $y - 1;
    return ($start % 100) . '/' . (($start % 100) + 1);
}

/** Sticky Default fuer Gueltig-bis: letzte verwendete, sonst 1. Okt End-Jahr Schuljahr. */
function lic_default_valid_until(Database $db): string {
    $last = $db->fetchOne("SELECT default_valid_until FROM license_batches WHERE default_valid_until IS NOT NULL ORDER BY id DESC LIMIT 1");
    if ($last && !empty($last['default_valid_until'])) return $last['default_valid_until'];
    $y = (int)date('Y'); $m = (int)date('n');
    $start = ($m >= 8) ? $y : $y - 1;
    return ($start + 1) . '-10-01';
}

/** Kunde finden (nach Kundennummer, dann Email) oder anlegen. Ergaenzt fehlende Felder. */
function lic_find_or_create_customer(Database $db, ?string $email, ?string $customerNo, ?string $name): ?int {
    $email = $email ? trim($email) : null;
    $customerNo = $customerNo ? trim($customerNo) : null;
    $name = $name ? trim($name) : null;
    if (!$email && !$customerNo && !$name) return null;
    $found = null;
    if ($customerNo) $found = $db->fetchOne("SELECT id FROM license_customers WHERE customer_no = ? LIMIT 1", [$customerNo]);
    if (!$found && $email) $found = $db->fetchOne("SELECT id FROM license_customers WHERE email = ? LIMIT 1", [$email]);
    if ($found) {
        $db->execute("UPDATE license_customers SET email = COALESCE(email, ?), customer_no = COALESCE(customer_no, ?), name = COALESCE(name, ?) WHERE id = ?",
            [$email, $customerNo, $name, $found['id']]);
        return (int)$found['id'];
    }
    $db->execute("INSERT INTO license_customers (customer_no, email, name) VALUES (?,?,?)", [$customerNo, $email, $name]);
    return (int)$db->lastInsertId();
}

/** Audit-Eintrag (erzeugt/verlaengert/storniert/gemailt/eingeloest). */
function lic_event(Database $db, ?int $batchId, ?int $licenseId, string $event, ?string $detail, ?int $adminId): void {
    $db->execute("INSERT INTO license_events (batch_id, license_id, event, detail, admin_id) VALUES (?,?,?,?,?)",
        [$batchId, $licenseId, $event, $detail, $adminId]);
}

/** Brute-Force-Bremse beim Einloesen: 10 Fehlversuche/10min pro IP, 20 pro Lehrer. */
function lic_throttle_check(Database $db, ?int $teacherId): void {
    $ip = $_SERVER['REMOTE_ADDR'] ?? '';
    if ($ip !== '') {
        $r = $db->fetchOne("SELECT COUNT(*) c FROM license_redeem_attempts WHERE ok=0 AND ip=INET6_ATON(?) AND created_at > (NOW() - INTERVAL 10 MINUTE)", [$ip]);
        if ($r && (int)$r['c'] >= 10) Response::error('Zu viele Fehlversuche. Bitte in ein paar Minuten erneut.', 429);
    }
    if ($teacherId) {
        $r = $db->fetchOne("SELECT COUNT(*) c FROM license_redeem_attempts WHERE ok=0 AND teacher_id=? AND created_at > (NOW() - INTERVAL 10 MINUTE)", [$teacherId]);
        if ($r && (int)$r['c'] >= 20) Response::error('Zu viele Fehlversuche. Bitte spaeter erneut.', 429);
    }
}

/** Einloese-Versuch protokollieren (fuer Schutz + Audit). */
function lic_attempt(Database $db, ?int $teacherId, string $code, bool $ok): void {
    $ip = $_SERVER['REMOTE_ADDR'] ?? '';
    $db->execute("INSERT INTO license_redeem_attempts (ip, teacher_id, code_tried, ok) VALUES (INET6_ATON(?), ?, ?, ?)",
        [$ip !== '' ? $ip : null, $teacherId, substr($code, 0, 32), $ok ? 1 : 0]);
}

// === GET ===
if ($method === 'GET') {
    // Super-Admin: alle Lizenzen
    if (isset($_GET['admin']) && $_GET['admin'] === '1') {
        $adminId = Session::adminId();
        if (!$adminId) {
            Response::error('Nicht autorisiert', 401);
        }

        // Vorbelegung fuer das Ausgabe-Formular (Sticky Gueltig-bis + Typen)
        if (isset($_GET['sales_default'])) {
            Response::ok([
                'valid_from'  => date('Y-m-d'),
                'valid_until' => lic_default_valid_until($db),
                'types'       => LIC_TYPES,
            ]);
        }

        // Kunden-Autocomplete
        if (isset($_GET['customers'])) {
            $like = '%' . trim($_GET['customers']) . '%';
            $rows = $db->fetchAll(
                "SELECT id, customer_no, email, name FROM license_customers
                 WHERE email LIKE ? OR name LIKE ? OR customer_no LIKE ?
                 ORDER BY name, email LIMIT 10", [$like, $like, $like]);
            Response::ok(['customers' => $rows]);
        }

        // Chargen-Uebersicht (mit Aggregaten + Filter)
        if (($_GET['view'] ?? '') === 'batches') {
            $where = '1=1'; $p = [];
            if (!empty($_GET['type']))     { $where .= ' AND b.sales_type = ?';   $p[] = $_GET['type']; }
            if (!empty($_GET['order_no'])) { $where .= ' AND b.order_no LIKE ?';   $p[] = '%' . $_GET['order_no'] . '%'; }
            if (!empty($_GET['customer'])) { $q = '%' . $_GET['customer'] . '%'; $where .= ' AND (c.email LIKE ? OR c.name LIKE ? OR c.customer_no LIKE ?)'; $p[] = $q; $p[] = $q; $p[] = $q; }
            $batches = $db->fetchAll(
                "SELECT b.id, b.order_no, b.sales_type, b.qty, b.default_valid_from, b.default_valid_until,
                        b.redeem_token, b.created_at, b.canceled_at, b.note,
                        c.email AS customer_email, c.name AS customer_name, c.customer_no,
                        COUNT(l.id) AS n_total,
                        SUM(l.canceled_at IS NOT NULL) AS n_canceled,
                        SUM(l.redeemed_at IS NOT NULL AND l.canceled_at IS NULL) AS n_redeemed,
                        SUM(l.canceled_at IS NULL AND l.valid_until IS NOT NULL AND l.valid_until < CURDATE()) AS n_expired
                 FROM license_batches b
                 LEFT JOIN license_customers c ON c.id = b.customer_id
                 LEFT JOIN licenses l ON l.batch_id = b.id
                 WHERE $where
                 GROUP BY b.id
                 ORDER BY b.id DESC
                 LIMIT 300", $p);
            Response::ok(['batches' => $batches]);
        }

        // Detail einer Charge: Codes + Verlauf + Mails
        if (($_GET['view'] ?? '') === 'batch_detail') {
            $bid = (int)($_GET['batch_id'] ?? 0);
            $batch = $db->fetchOne(
                "SELECT b.*, c.email AS customer_email, c.name AS customer_name, c.customer_no
                 FROM license_batches b LEFT JOIN license_customers c ON c.id = b.customer_id
                 WHERE b.id = ?", [$bid]);
            if (!$batch) Response::error('Charge nicht gefunden', 404);
            $codes = $db->fetchAll(
                "SELECT l.id, l.code, l.valid_from, l.valid_until, l.issued_at, l.redeemed_at,
                        l.student_id, l.teacher_id, l.canceled_at, l.canceled_reason,
                        t.display_name AS teacher_name, s.username AS student_name
                 FROM licenses l
                 LEFT JOIN teachers t ON t.id = l.teacher_id
                 LEFT JOIN students s ON s.id = l.student_id
                 WHERE l.batch_id = ? ORDER BY l.id", [$bid]);
            $events = $db->fetchAll("SELECT event, detail, admin_id, created_at FROM license_events WHERE batch_id = ? ORDER BY id DESC LIMIT 100", [$bid]);
            $mails  = $db->fetchAll("SELECT id, to_email, subject, status, error, created_at, sent_at FROM license_mails WHERE batch_id = ? ORDER BY id DESC", [$bid]);
            Response::ok(['batch' => $batch, 'codes' => $codes, 'events' => $events, 'mails' => $mails]);
        }

        $year = $_GET['year'] ?? null;
        $status = $_GET['status'] ?? null; // 'free', 'used'

        $where = '1=1';
        $params = [];
        if ($year) { $where .= ' AND l.school_year = ?'; $params[] = $year; }
        if ($status === 'free') { $where .= ' AND l.student_id IS NULL'; }
        if ($status === 'used') { $where .= ' AND l.student_id IS NOT NULL'; }

        $total = $db->fetchOne("SELECT COUNT(*) as c FROM licenses l WHERE $where", $params);
        $free = $db->fetchOne("SELECT COUNT(*) as c FROM licenses l WHERE student_id IS NULL" . ($year ? " AND school_year = ?" : ""), $year ? [$year] : []);
        $used = $db->fetchOne("SELECT COUNT(*) as c FROM licenses l WHERE student_id IS NOT NULL" . ($year ? " AND school_year = ?" : ""), $year ? [$year] : []);

        $limit = (int)($_GET['limit'] ?? 100);
        $offset = (int)($_GET['offset'] ?? 0);

        $licenses = $db->fetchAll(
            "SELECT l.id, l.code, l.school_year, l.student_id, l.teacher_id, l.redeemed_at, l.created_at,
                    s.username as student_name, t.display_name as teacher_name
             FROM licenses l
             LEFT JOIN students s ON s.id = l.student_id
             LEFT JOIN teachers t ON t.id = l.teacher_id
             WHERE $where
             ORDER BY l.id DESC
             LIMIT $limit OFFSET $offset",
            $params
        );

        Response::ok([
            'total' => (int)$total['c'],
            'free' => (int)$free['c'],
            'used' => (int)$used['c'],
            'licenses' => $licenses
        ]);
    }

    // Lehrer: Lizenzen einer Klasse
    $teacherId = Session::requireTeacher();
    $classId = (int)($_GET['class_id'] ?? 0);
    if (!$classId) Response::error('class_id erforderlich');

    $class = $db->fetchOne('SELECT id FROM classes WHERE id = ? AND teacher_id = ?', [$classId, $teacherId]);
    if (!$class) Response::error('Klasse nicht gefunden', 404);

    $licenses = $db->fetchAll(
        'SELECT l.id, l.code, l.school_year, l.student_id, l.redeemed_at,
                s.username as student_name, s.display_name as student_display
         FROM licenses l
         JOIN students s ON s.id = l.student_id
         WHERE s.class_id = ?
         ORDER BY s.username',
        [$classId]
    );

    // Auch freie Lizenzen des Lehrers (noch nicht zugewiesen)
    $freeLicenses = $db->fetchAll(
        'SELECT id, code, school_year FROM licenses WHERE teacher_id = ? AND student_id IS NULL ORDER BY code',
        [$teacherId]
    );

    Response::ok(['assigned' => $licenses, 'free' => $freeLicenses]);
}

// === POST ===
if ($method === 'POST') {
    $body = json_decode(file_get_contents('php://input'), true);
    $action = $body['action'] ?? '';

    // Lizenz einlösen (Lehrer gibt Code ein → wird ihm zugeordnet)
    if ($action === 'redeem') {
        $teacherId = Session::requireTeacher();
        $code = strtoupper(trim($body['code'] ?? ''));
        if (!$code) Response::error('Lizenzcode erforderlich');
        lic_throttle_check($db, $teacherId);

        $license = $db->fetchOne('SELECT id, batch_id, student_id, teacher_id, canceled_at FROM licenses WHERE code = ?', [$code]);
        if (!$license)               { lic_attempt($db, $teacherId, $code, false); Response::error('Lizenzcode ungültig'); }
        if ($license['canceled_at']) { lic_attempt($db, $teacherId, $code, false); Response::error('Dieser Lizenzcode wurde storniert'); }
        if ($license['student_id'])  { lic_attempt($db, $teacherId, $code, false); Response::error('Diese Lizenz ist bereits zugewiesen'); }
        if ($license['teacher_id'] && $license['teacher_id'] != $teacherId) { lic_attempt($db, $teacherId, $code, false); Response::error('Diese Lizenz gehört einer anderen Lehrperson'); }

        $db->execute('UPDATE licenses SET teacher_id = ?, redeemed_at = NOW() WHERE id = ?', [$teacherId, $license['id']]);
        lic_attempt($db, $teacherId, $code, true);
        lic_event($db, $license['batch_id'] ? (int)$license['batch_id'] : null, (int)$license['id'], 'redeemed', 'durch Lehrer #' . $teacherId, null);
        Response::ok(['licenseId' => (int)$license['id']]);
    }

    // Mehrere Lizenzen auf einmal einlösen
    if ($action === 'redeem_batch') {
        $teacherId = Session::requireTeacher();
        $codes = $body['codes'] ?? [];
        if (!is_array($codes) || empty($codes)) Response::error('Lizenzcodes erforderlich');
        lic_throttle_check($db, $teacherId);

        $redeemed = 0;
        $errors = [];
        foreach ($codes as $code) {
            $code = strtoupper(trim($code));
            if (!$code) continue;
            $license = $db->fetchOne('SELECT id, student_id, teacher_id, canceled_at FROM licenses WHERE code = ?', [$code]);
            if (!$license)               { lic_attempt($db, $teacherId, $code, false); $errors[] = "$code: ungültig"; continue; }
            if ($license['canceled_at']) { lic_attempt($db, $teacherId, $code, false); $errors[] = "$code: storniert"; continue; }
            if ($license['student_id'])  { lic_attempt($db, $teacherId, $code, false); $errors[] = "$code: bereits zugewiesen"; continue; }
            if ($license['teacher_id'] && $license['teacher_id'] != $teacherId) { lic_attempt($db, $teacherId, $code, false); $errors[] = "$code: gehört anderer Lehrperson"; continue; }
            $db->execute('UPDATE licenses SET teacher_id = ?, redeemed_at = NOW() WHERE id = ?', [$teacherId, $license['id']]);
            lic_attempt($db, $teacherId, $code, true);
            $redeemed++;
        }
        Response::ok(['redeemed' => $redeemed, 'errors' => $errors]);
    }

    // Lizenz einem Schüler zuweisen
    if ($action === 'assign') {
        $teacherId = Session::requireTeacher();
        $licenseId = (int)($body['licenseId'] ?? 0);
        $studentId = (int)($body['studentId'] ?? 0);
        if (!$licenseId || !$studentId) Response::error('licenseId und studentId erforderlich');

        $license = $db->fetchOne('SELECT id, teacher_id FROM licenses WHERE id = ? AND student_id IS NULL', [$licenseId]);
        if (!$license) Response::error('Lizenz nicht gefunden oder bereits zugewiesen');
        if ($license['teacher_id'] && $license['teacher_id'] != $teacherId) Response::error('Lizenz gehört anderer Lehrperson');

        // Prüfen dass Schüler dem Lehrer gehört
        $student = $db->fetchOne(
            'SELECT s.id FROM students s JOIN classes c ON c.id = s.class_id WHERE s.id = ? AND c.teacher_id = ?',
            [$studentId, $teacherId]
        );
        if (!$student) Response::error('Schüler*in nicht gefunden');

        $db->execute('UPDATE licenses SET student_id = ?, teacher_id = ? WHERE id = ?', [$studentId, $teacherId, $licenseId]);
        Response::ok();
    }

    // Auto-Assign: nächste freie Lizenz einem Schüler zuweisen
    if ($action === 'auto_assign') {
        $teacherId = Session::requireTeacher();
        $studentId = (int)($body['studentId'] ?? 0);
        if (!$studentId) Response::error('studentId erforderlich');

        $student = $db->fetchOne(
            'SELECT s.id FROM students s JOIN classes c ON c.id = s.class_id WHERE s.id = ? AND c.teacher_id = ?',
            [$studentId, $teacherId]
        );
        if (!$student) Response::error('Schüler*in nicht gefunden');

        // Nächste freie Lizenz des Lehrers
        $license = $db->fetchOne(
            'SELECT id FROM licenses WHERE teacher_id = ? AND student_id IS NULL ORDER BY id LIMIT 1',
            [$teacherId]
        );
        if (!$license) Response::error('Keine freien Lizenzen verfügbar');

        $db->execute('UPDATE licenses SET student_id = ? WHERE id = ?', [$studentId, $license['id']]);
        Response::ok(['licenseId' => (int)$license['id']]);
    }

    // Super-Admin: neue Lizenzen generieren (NUR echter Admin)
    if ($action === 'generate') {
        if (!Session::adminId()) Response::error('Nur Admin', 403);
        $count = min(1000, max(1, (int)($body['count'] ?? 100)));
        $year = (int)($body['year'] ?? date('Y'));
        $schoolYear = ($year % 100) . '/' . (($year % 100) + 1);

        $chars = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789';
        $generated = 0; $tries = 0; $maxTries = $count * 10 + 100;
        while ($generated < $count && $tries < $maxTries) {
            $tries++;
            $code = '';
            for ($j = 0; $j < 3; $j++) {
                if ($j > 0) $code .= '-';
                for ($k = 0; $k < 4; $k++) $code .= $chars[random_int(0, strlen($chars) - 1)];
            }
            $code .= '-' . $year;
            try {
                $db->execute('INSERT INTO licenses (code, school_year) VALUES (?, ?)', [$code, $schoolYear]);
                $generated++;
            } catch (\Exception $e) {
                // Kollision (unwahrscheinlich) → nächster Versuch; $maxTries schützt vor Endlosschleife
            }
        }
        Response::ok(['generated' => $generated]);
    }

    // ═══════════════ Vertrieb: Charge ausgeben ═══════════════
    if ($action === 'issue_batch') {
        $adminId = Session::adminId();
        if (!$adminId) Response::error('Nur Admin', 403);

        $count = (int)($body['count'] ?? 0);
        if ($count < 1 || $count > 5000) Response::error('Anzahl muss zwischen 1 und 5000 liegen');
        $type = in_array($body['sales_type'] ?? '', LIC_TYPES, true) ? $body['sales_type'] : 'privat';
        $orderNo = trim((string)($body['order_no'] ?? '')) ?: null;
        $note = trim((string)($body['note'] ?? '')) ?: null;
        $validFrom  = !empty($body['valid_from'])  ? $body['valid_from']  : date('Y-m-d');
        $validUntil = !empty($body['valid_until']) ? $body['valid_until'] : lic_default_valid_until($db);
        if (!strtotime($validFrom) || !strtotime($validUntil)) Response::error('Ungültiges Datum');
        if (strtotime($validUntil) < strtotime($validFrom)) Response::error('„Gültig bis" liegt vor „Gültig von"');

        $cust = is_array($body['customer'] ?? null) ? $body['customer'] : [];
        $customerId = lic_find_or_create_customer($db, $cust['email'] ?? null, $cust['customer_no'] ?? null, $cust['name'] ?? null);
        $schoolYear = lic_school_year_from($validFrom);
        $token = bin2hex(random_bytes(20));

        $db->begin();
        try {
            $db->execute(
                "INSERT INTO license_batches (customer_id, order_no, sales_type, qty, default_valid_from, default_valid_until, note, redeem_token, created_by)
                 VALUES (?,?,?,?,?,?,?,?,?)",
                [$customerId, $orderNo, $type, $count, $validFrom, $validUntil, $note, $token, $adminId]);
            $batchId = (int)$db->lastInsertId();

            $codes = []; $made = 0; $tries = 0; $maxTries = $count * 8 + 50;
            while ($made < $count && $tries < $maxTries) {
                $tries++;
                $code = lic_new_code();
                try {
                    $db->execute(
                        "INSERT INTO licenses (code, school_year, batch_id, issued_at, valid_from, valid_until) VALUES (?,?,?,NOW(),?,?)",
                        [$code, $schoolYear, $batchId, $validFrom, $validUntil]);
                    $codes[] = $code; $made++;
                } catch (\Throwable $e) { /* Code-Kollision (extrem selten) → neuer Versuch */ }
            }
            if ($made < $count) throw new \RuntimeException("Nur $made von $count Codes erzeugt");
            lic_event($db, $batchId, null, 'issued', "$count Codes, gültig $validFrom…$validUntil, Typ $type" . ($orderNo ? ", Best.-Nr. $orderNo" : ''), $adminId);
            $db->commit();
        } catch (\Throwable $e) {
            $db->rollBack();
            Response::error('Fehler beim Erzeugen: ' . $e->getMessage(), 500);
        }
        Response::ok([
            'batch_id' => $batchId, 'redeem_token' => $token,
            'valid_from' => $validFrom, 'valid_until' => $validUntil,
            'count' => $made, 'codes' => $codes,
        ]);
    }

    // ═══════════════ Storno ═══════════════
    if ($action === 'cancel_batch') {
        $adminId = Session::adminId(); if (!$adminId) Response::error('Nur Admin', 403);
        $bid = (int)($body['batch_id'] ?? 0); if (!$bid) Response::error('batch_id erforderlich');
        $reason = trim((string)($body['reason'] ?? '')) ?: null;
        $n = $db->execute("UPDATE licenses SET canceled_at = NOW(), canceled_reason = ? WHERE batch_id = ? AND canceled_at IS NULL", [$reason, $bid]);
        $db->execute("UPDATE license_batches SET canceled_at = NOW(), canceled_reason = ? WHERE id = ?", [$reason, $bid]);
        lic_event($db, $bid, null, 'canceled', "Charge storniert ($n Codes)" . ($reason ? ": $reason" : ''), $adminId);
        Response::ok(['canceled' => $n]);
    }

    if ($action === 'cancel_license') {
        $adminId = Session::adminId(); if (!$adminId) Response::error('Nur Admin', 403);
        $lid = (int)($body['license_id'] ?? 0); if (!$lid) Response::error('license_id erforderlich');
        $reason = trim((string)($body['reason'] ?? '')) ?: null;
        $lic = $db->fetchOne("SELECT batch_id FROM licenses WHERE id = ?", [$lid]);
        if (!$lic) Response::error('Code nicht gefunden', 404);
        $db->execute("UPDATE licenses SET canceled_at = NOW(), canceled_reason = ? WHERE id = ? AND canceled_at IS NULL", [$reason, $lid]);
        lic_event($db, $lic['batch_id'] ? (int)$lic['batch_id'] : null, $lid, 'canceled', 'Einzel-Storno' . ($reason ? ": $reason" : ''), $adminId);
        Response::ok();
    }

    // ═══════════════ Verlängern ═══════════════
    if ($action === 'extend_license') {
        $adminId = Session::adminId(); if (!$adminId) Response::error('Nur Admin', 403);
        $lid = (int)($body['license_id'] ?? 0); $vu = $body['valid_until'] ?? '';
        if (!$lid || !strtotime($vu)) Response::error('license_id + valid_until erforderlich');
        $lic = $db->fetchOne("SELECT batch_id, valid_until FROM licenses WHERE id = ?", [$lid]);
        if (!$lic) Response::error('Code nicht gefunden', 404);
        $db->execute("UPDATE licenses SET valid_until = ? WHERE id = ?", [$vu, $lid]);
        lic_event($db, $lic['batch_id'] ? (int)$lic['batch_id'] : null, $lid, 'extended', 'valid_until ' . ($lic['valid_until'] ?? '—') . " → $vu", $adminId);
        Response::ok();
    }

    if ($action === 'extend_batch') {
        $adminId = Session::adminId(); if (!$adminId) Response::error('Nur Admin', 403);
        $bid = (int)($body['batch_id'] ?? 0); $vu = $body['valid_until'] ?? '';
        if (!$bid || !strtotime($vu)) Response::error('batch_id + valid_until erforderlich');
        $n = $db->execute("UPDATE licenses SET valid_until = ? WHERE batch_id = ? AND canceled_at IS NULL", [$vu, $bid]);
        $db->execute("UPDATE license_batches SET default_valid_until = ? WHERE id = ?", [$vu, $bid]);
        lic_event($db, $bid, null, 'extended', "Charge verlängert auf $vu ($n Codes)", $adminId);
        Response::ok(['updated' => $n]);
    }

    // ═══════════════ Mailversand (Server-Treiber, archiviert) ═══════════════
    if ($action === 'send_batch_mail') {
        $adminId = Session::adminId(); if (!$adminId) Response::error('Nur Admin', 403);
        $bid = (int)($body['batch_id'] ?? 0); if (!$bid) Response::error('batch_id erforderlich');
        $to = trim((string)($body['to_email'] ?? ''));
        $subject = trim((string)($body['subject'] ?? '')) ?: 'Ihre GeoGraSim-Lizenzcodes';
        $textBody = (string)($body['body_text'] ?? '');
        if (!filter_var($to, FILTER_VALIDATE_EMAIL)) Response::error('Gültige Empfänger-Mailadresse erforderlich');
        if (trim($textBody) === '') Response::error('Mailtext ist leer');

        $codeRows = $db->fetchAll("SELECT code FROM licenses WHERE batch_id = ? AND canceled_at IS NULL ORDER BY id", [$bid]);
        $codeList = array_map(fn($r) => $r['code'], $codeRows);
        $html = Mailer::renderPlainBody($textBody);
        $attach = [];
        if (count($codeList) > 40) {
            $attach[] = ['content' => implode("\r\n", $codeList) . "\r\n", 'name' => 'lizenzcodes.txt', 'type' => 'text/plain'];
        }
        $db->execute(
            "INSERT INTO license_mails (batch_id, to_email, subject, body_text, body_html, provider, status, created_by) VALUES (?,?,?,?,?,?,?,?)",
            [$bid, $to, $subject, $textBody, $html, 'server', 'queued', $adminId]);
        $mailId = (int)$db->lastInsertId();
        try {
            Mailer::sendWithAttachments($to, $subject, $html, $textBody, $attach);
            $db->execute("UPDATE license_mails SET status='sent', sent_at=NOW() WHERE id=?", [$mailId]);
            lic_event($db, $bid, null, 'mailed', "an $to", $adminId);
            Response::ok(['mail_id' => $mailId, 'status' => 'sent']);
        } catch (\Throwable $e) {
            $db->execute("UPDATE license_mails SET status='failed', error=? WHERE id=?", [substr($e->getMessage(), 0, 240), $mailId]);
            Response::error('Versand fehlgeschlagen: ' . $e->getMessage(), 500);
        }
    }

    // ═══════════════ Sammel-Einlösen einer Charge (ein Link → alle Codes) ═══════════════
    if ($action === 'redeem_charge') {
        $teacherId = Session::requireTeacher();
        $token = trim((string)($body['token'] ?? ''));
        if ($token === '') Response::error('Token erforderlich');
        lic_throttle_check($db, $teacherId);
        $batch = $db->fetchOne("SELECT id FROM license_batches WHERE redeem_token = ? AND canceled_at IS NULL", [$token]);
        if (!$batch) { lic_attempt($db, $teacherId, 'charge:' . substr($token, 0, 24), false); Response::error('Einlöse-Link ungültig oder storniert'); }
        $n = $db->execute(
            "UPDATE licenses SET teacher_id = ?, redeemed_at = COALESCE(redeemed_at, NOW())
             WHERE batch_id = ? AND canceled_at IS NULL AND (teacher_id IS NULL OR teacher_id = ?)",
            [$teacherId, $batch['id'], $teacherId]);
        lic_attempt($db, $teacherId, 'charge:' . substr($token, 0, 24), true);
        lic_event($db, (int)$batch['id'], null, 'redeemed', "Charge-Sammellink durch Lehrer #$teacherId ($n Codes)", null);
        Response::ok(['redeemed' => $n]);
    }

    Response::error('Unbekannte Aktion');
}

Response::error('Methode nicht erlaubt', 405);