<?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();

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

        $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');

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

        $db->execute('UPDATE licenses SET teacher_id = ?, redeemed_at = NOW() WHERE id = ?', [$teacherId, $license['id']]);
        Response::ok(['licenseId' => (int)$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');

        $redeemed = 0;
        $errors = [];
        foreach ($codes as $code) {
            $code = strtoupper(trim($code));
            if (!$code) continue;
            $license = $db->fetchOne('SELECT id, student_id, teacher_id FROM licenses WHERE code = ?', [$code]);
            if (!$license) { $errors[] = "$code: ungültig"; continue; }
            if ($license['student_id']) { $errors[] = "$code: bereits zugewiesen"; continue; }
            if ($license['teacher_id'] && $license['teacher_id'] != $teacherId) { $errors[] = "$code: gehört anderer Lehrperson"; continue; }
            $db->execute('UPDATE licenses SET teacher_id = ?, redeemed_at = NOW() WHERE id = ?', [$teacherId, $license['id']]);
            $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
    if ($action === 'generate') {
        $teacherId = Session::requireTeacher();
        $count = min(1000, max(1, (int)($body['count'] ?? 100)));
        $year = (int)($body['year'] ?? date('Y'));
        $schoolYear = ($year % 100) . '/' . (($year % 100) + 1);

        $chars = 'ABCDEFGHJKLMNPQRSTUVWXYZ23456789';
        $generated = 0;
        for ($i = 0; $i < $count; $i++) {
            $code = '';
            for ($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) {
                $i--; // Collision, retry
            }
        }
        Response::ok(['generated' => $generated]);
    }

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

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