<?php
/**
 * API: Schueler-Verwaltung (nur fuer Lehrer)
 * GET    /api/students?class_id=X   → Alle Schueler einer Klasse
 * POST   /api/students {action}     → Schueler erstellen/bearbeiten/loeschen
 */

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

// Zufälliger Bild-Avatar im Plattform-Bildstil (siehe assets/img/avatars/).
// Slug-Liste deckungsgleich mit AVATAR_GROUPS in profil.html.
function ggs_random_avatar_slug(): string {
    static $slugs = [
        'pilotin','pilot','kartografin','geologe','meteorologin','stadtplaner','forscherin','forscher','taucherin','astronaut',
        'coole-girl','coole-boy','lustige-girl','lustige-boy','nerd-girl','sportlich-boy','kuenstlerin','musiker','gaertnerin','abenteurer',
        'fuchs-explorer','eule-prof','baer-foerster','pinguin-polar','affe-tropen','delfin-meer','adler-pilot','schildkroete-w','katze-stadt','biene-natur'
    ];
    return 'avatar:' . $slugs[array_rand($slugs)];
}

if ($method === 'GET') {
    $teacherId = Session::requireTeacher();
    $classId = (int)($_GET['class_id'] ?? 0);
    if (!$classId) Response::error('class_id erforderlich');

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

    $students = $db->fetchAll(
        'SELECT id, username, display_name, first_name, last_name, email, emoji_avatar, is_anonymous, easy_language, password_plaintext, created_at, last_login FROM students WHERE class_id = ? AND deleted_at IS NULL ORDER BY username',
        [$classId]
    );

    // Letzte Ergebnisse pro Schueler
    foreach ($students as &$s) {
        $s['results'] = $db->fetchAll(
            'SELECT module_id, score, balance_idx, completed_at FROM student_results WHERE student_id = ? ORDER BY completed_at DESC LIMIT 10',
            [$s['id']]
        );
        $s['total_score'] = $db->fetchOne(
            'SELECT AVG(score) as avg_score, COUNT(*) as count FROM student_results WHERE student_id = ?',
            [$s['id']]
        );
    }

    Response::ok($students);
}

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

    // === SCHUELER ERSTELLEN ===
    if ($action === 'create') {
        $classId = (int)($body['classId'] ?? 0);
        $username = mb_substr(trim($body['username'] ?? ''), 0, 64);
        $password = $body['password'] ?? '';
        $displayName = mb_substr(trim($body['displayName'] ?? ''), 0, 128);
        $firstName = mb_substr(trim($body['firstName'] ?? ''), 0, 64);
        $lastName = mb_substr(trim($body['lastName'] ?? ''), 0, 64);
        $email = trim($body['email'] ?? '');
        $isAnonymous = (bool)($body['isAnonymous'] ?? (!$firstName && !$lastName));

        if (!$classId || !$username || !$password) Response::error('classId, username und password erforderlich');
        if (strlen($password) < 4) Response::error('Passwort muss mindestens 4 Zeichen lang sein');
        if ($email && !filter_var($email, FILTER_VALIDATE_EMAIL)) Response::error('Ungültige E-Mail-Adresse');

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

        // Username eindeutig in Klasse?
        $existing = $db->fetchOne('SELECT id FROM students WHERE class_id = ? AND username = ?', [$classId, $username]);
        if ($existing) Response::error('Benutzername in dieser Klasse bereits vergeben');

        $hash = password_hash($password, PASSWORD_DEFAULT);
        $avatar = ggs_random_avatar_slug();
        $db->execute(
            'INSERT INTO students (class_id, username, password, password_plaintext, display_name, first_name, last_name, email, is_anonymous, emoji_avatar) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?)',
            [$classId, $username, $hash, $password, $displayName ?: null, $firstName ?: null, $lastName ?: null, $email ?: null, $isAnonymous ? 1 : 0, $avatar]
        );
        Response::ok(['id' => (int)$db->lastInsertId(), 'emoji_avatar' => $avatar]);
    }

    // === CSV-IMPORT — pro Zeile einen Schüler ===
    if ($action === 'create_csv') {
        $classId = (int)($body['classId'] ?? 0);
        $rows = $body['rows'] ?? [];
        if (!is_array($rows) || !$rows) Response::error('keine Zeilen');

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

        $created = [];
        $skipped = [];
        foreach ($rows as $r) {
            $username    = mb_substr(trim($r['username']     ?? ''), 0, 64);
            $password    = trim($r['password']     ?? '');
            $displayName = mb_substr(trim($r['display_name'] ?? ''), 0, 128);
            $firstName   = mb_substr(trim($r['first_name']   ?? ''), 0, 64);
            $lastName    = mb_substr(trim($r['last_name']    ?? ''), 0, 64);
            $email       = trim($r['email']        ?? '');
            $easy        = !empty($r['easy']) && $r['easy'] !== '0';
            if (!$username) { $skipped[] = ['row' => $r, 'reason' => 'kein username']; continue; }
            if ($email && !filter_var($email, FILTER_VALIDATE_EMAIL)) { $skipped[] = ['row' => $r, 'reason' => 'ungueltige E-Mail']; continue; }
            $existing = $db->fetchOne('SELECT id FROM students WHERE class_id = ? AND username = ?', [$classId, $username]);
            if ($existing) { $skipped[] = ['row' => $r, 'reason' => 'username existiert bereits']; continue; }

            // Passwort: angegeben oder 4-Ziffern-Generat
            if (!$password) $password = str_pad((string)random_int(1000, 9999), 4, '0', STR_PAD_LEFT);
            if (strlen($password) < 4) { $skipped[] = ['row' => $r, 'reason' => 'Passwort zu kurz']; continue; }
            $hash = password_hash($password, PASSWORD_DEFAULT);

            $isAnonymous = !$firstName && !$lastName;
            $avatar = ggs_random_avatar_slug();
            $db->execute(
                'INSERT INTO students (class_id, username, password, password_plaintext, display_name, first_name, last_name, email, is_anonymous, easy_language, emoji_avatar) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)',
                [$classId, $username, $hash, $password, $displayName ?: $username, $firstName ?: null, $lastName ?: null, $email ?: null, $isAnonymous ? 1 : 0, $easy ? 1 : 0, $avatar]
            );
            $created[] = ['username' => $username, 'password' => $password, 'displayName' => $displayName ?: $username, 'id' => (int)$db->lastInsertId(), 'emoji_avatar' => $avatar];
        }
        Response::ok(['created' => $created, 'skipped' => $skipped]);
    }

    // === MEHRERE SCHUELER AUF EINMAL ERSTELLEN ===
    if ($action === 'create_batch') {
        $classId = (int)($body['classId'] ?? 0);
        $count = min(50, max(1, (int)($body['count'] ?? 10)));
        $prefix = mb_substr(trim($body['prefix'] ?? 'schueler'), 0, 20);

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

        $created = [];
        for ($i = 1; $i <= $count; $i++) {
            $username = $prefix . str_pad($i, 2, '0', STR_PAD_LEFT);
            // Einfaches Passwort generieren (4 Ziffern)
            $pw = str_pad(random_int(1000, 9999), 4, '0', STR_PAD_LEFT);
            $hash = password_hash($pw, PASSWORD_DEFAULT);

            $existing = $db->fetchOne('SELECT id FROM students WHERE class_id = ? AND username = ?', [$classId, $username]);
            if ($existing) continue; // Ueberspringen wenn schon vorhanden

            $avatar = ggs_random_avatar_slug();
            $db->execute(
                'INSERT INTO students (class_id, username, password, password_plaintext, display_name, is_anonymous, emoji_avatar) VALUES (?, ?, ?, ?, ?, 1, ?)',
                [$classId, $username, $hash, $pw, $username, $avatar]
            );
            $created[] = ['username' => $username, 'password' => $pw, 'id' => (int)$db->lastInsertId(), 'emoji_avatar' => $avatar];
        }
        Response::ok(['created' => $created]);
    }

    // === SCHUELER BEARBEITEN ===
    if ($action === 'update') {
        $studentId = (int)($body['studentId'] ?? 0);
        $displayName = mb_substr(trim($body['displayName'] ?? ''), 0, 128);
        $newPassword = $body['newPassword'] ?? '';

        // Schueler + Klasse pruefen
        $student = $db->fetchOne(
            'SELECT s.id, s.class_id FROM students s JOIN classes c ON c.id = s.class_id WHERE s.id = ? AND c.teacher_id = ?',
            [$studentId, $teacherId]
        );
        if (!$student) Response::error('Schüler nicht gefunden', 404);

        $firstName = mb_substr(trim($body['firstName'] ?? ''), 0, 64);
        $lastName = mb_substr(trim($body['lastName'] ?? ''), 0, 64);
        $email = trim($body['email'] ?? '');
        $emojiAvatar = mb_substr(trim($body['emojiAvatar'] ?? ''), 0, 8);

        if ($displayName) {
            $db->execute('UPDATE students SET display_name = ? WHERE id = ?', [$displayName, $studentId]);
        }
        if ($firstName !== '') {
            $db->execute('UPDATE students SET first_name = ? WHERE id = ?', [$firstName, $studentId]);
        }
        if ($lastName !== '') {
            $db->execute('UPDATE students SET last_name = ? WHERE id = ?', [$lastName, $studentId]);
        }
        if ($email !== '') {
            if (!filter_var($email, FILTER_VALIDATE_EMAIL)) Response::error('Ungültige E-Mail-Adresse');
            $db->execute('UPDATE students SET email = ? WHERE id = ?', [$email, $studentId]);
        }
        if ($emojiAvatar !== '') {
            $db->execute('UPDATE students SET emoji_avatar = ? WHERE id = ?', [$emojiAvatar, $studentId]);
        }
        if ($newPassword && strlen($newPassword) >= 4) {
            $db->execute(
                'UPDATE students SET password = ?, password_plaintext = ? WHERE id = ?',
                [password_hash($newPassword, PASSWORD_DEFAULT), $newPassword, $studentId]
            );
        }
        // Leichte Sprache (nur setzen wenn Feld mitgeschickt)
        if (array_key_exists('easyLanguage', $body)) {
            $flag = !empty($body['easyLanguage']) ? 1 : 0;
            $db->execute('UPDATE students SET easy_language = ? WHERE id = ?', [$flag, $studentId]);
        }
        Response::ok();
    }

    // === PASSWORT EINES SCHUELERS ZURUECKSETZEN ===
    if ($action === 'reset_password') {
        $studentId = (int)($body['studentId'] ?? 0);
        $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 nicht gefunden', 404);

        $pw = str_pad((string)random_int(1000, 9999), 4, '0', STR_PAD_LEFT);
        $hash = password_hash($pw, PASSWORD_DEFAULT);
        $db->execute(
            'UPDATE students SET password = ?, password_plaintext = ? WHERE id = ?',
            [$hash, $pw, $studentId]
        );
        Response::ok(['password' => $pw]);
    }

    // === PASSWOERTER EINER AUSWAHL (oder alle der Klasse) ZURUECKSETZEN ===
    if ($action === 'reset_class_passwords') {
        $classId = (int)($body['classId'] ?? 0);
        $studentIds = $body['studentIds'] ?? null;  // optional: array von ids
        $class = $db->fetchOne('SELECT id FROM classes WHERE id = ? AND teacher_id = ?', [$classId, $teacherId]);
        if (!$class) Response::error('Klasse nicht gefunden', 404);

        if (is_array($studentIds) && $studentIds) {
            $studentIds = array_values(array_filter(array_map('intval', $studentIds)));
            if (!$studentIds) Response::error('Keine gültigen IDs');
            $placeholders = implode(',', array_fill(0, count($studentIds), '?'));
            $params = array_merge([$classId], $studentIds);
            $students = $db->fetchAll(
                "SELECT id, username, display_name, emoji_avatar FROM students
                 WHERE class_id = ? AND deleted_at IS NULL AND id IN ($placeholders) ORDER BY username",
                $params
            );
        } else {
            $students = $db->fetchAll(
                'SELECT id, username, display_name, emoji_avatar FROM students WHERE class_id = ? AND deleted_at IS NULL ORDER BY username',
                [$classId]
            );
        }
        $reset = [];
        foreach ($students as $s) {
            $pw = str_pad((string)random_int(1000, 9999), 4, '0', STR_PAD_LEFT);
            $hash = password_hash($pw, PASSWORD_DEFAULT);
            $db->execute(
                'UPDATE students SET password = ?, password_plaintext = ? WHERE id = ?',
                [$hash, $pw, $s['id']]
            );
            $reset[] = [
                'id' => (int)$s['id'],
                'username' => $s['username'],
                'displayName' => $s['display_name'] ?: $s['username'],
                'emoji' => $s['emoji_avatar'] ?: '🧑‍🎓',
                'password' => $pw,
            ];
        }
        Response::ok(['reset' => $reset]);
    }

    // === SCHUELER LOESCHEN ===
    if ($action === 'delete') {
        $studentId = (int)($body['studentId'] ?? 0);
        $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 nicht gefunden', 404);

        $db->execute('UPDATE students SET deleted_at = NOW() WHERE id = ?', [$studentId]);
        Response::ok();
    }

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

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