<?php
/**
 * API: Klassen-Simulationen (Aufgaben/Hausübungen)
 * GET  /api/assignments?class_id=X         → Aktive Aufgaben einer Klasse
 * GET  /api/assignments?student=1          → Aufgaben für eingeloggten Schüler*in
 * POST /api/assignments {action}           → Aufgabe erstellen/beenden
 */

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

if ($method === 'GET') {
    // Schüler*innen-Ansicht
    if (isset($_GET['student']) && $_GET['student'] === '1') {
        $sessionId = Session::requireStudent();
        $session = $db->fetchOne('SELECT class_id FROM student_sessions WHERE id = ?', [$sessionId]);
        if (!$session || !$session['class_id']) Response::ok([]);

        $assignments = $db->fetchAll(
            'SELECT a.id, a.module_id, a.level, a.starts_at, a.ends_at, a.created_at
             FROM class_assignments a
             WHERE a.class_id = ? AND a.active = 1 AND a.starts_at <= NOW() AND (a.ends_at IS NULL OR a.ends_at > NOW())
             ORDER BY a.created_at DESC',
            [$session['class_id']]
        );
        Response::ok($assignments);
    }

    // Lehrperson-Ansicht
    $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);

    $assignments = $db->fetchAll(
        'SELECT id, module_id, level, starts_at, ends_at, active, created_at FROM class_assignments WHERE class_id = ? ORDER BY created_at DESC',
        [$classId]
    );
    Response::ok($assignments);
}

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

    if ($action === 'create') {
        $classId = (int)($body['classId'] ?? 0);
        $moduleId = $body['moduleId'] ?? '';
        $level = max(1, min(5, (int)($body['level'] ?? 1)));
        // datetime-local liefert 'YYYY-MM-DDTHH:MM' → 'T' für MySQL zu Leerzeichen.
        $endsAt   = !empty($body['endsAt'])   ? str_replace('T', ' ', $body['endsAt'])   : null;
        $startsAt = !empty($body['startsAt']) ? str_replace('T', ' ', $body['startsAt']) : null;

        if (!$classId || !$moduleId) Response::error('classId und moduleId erforderlich');

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

        // Vorherige aktive Aufgabe für dieses Modul deaktivieren
        $db->execute(
            'UPDATE class_assignments SET active = 0 WHERE class_id = ? AND module_id = ? AND active = 1',
            [$classId, $moduleId]
        );

        if ($startsAt) {
            $db->execute(
                'INSERT INTO class_assignments (class_id, teacher_id, module_id, level, starts_at, ends_at) VALUES (?, ?, ?, ?, ?, ?)',
                [$classId, $teacherId, $moduleId, $level, $startsAt, $endsAt]
            );
        } else {
            $db->execute(
                'INSERT INTO class_assignments (class_id, teacher_id, module_id, level, starts_at, ends_at) VALUES (?, ?, ?, ?, NOW(), ?)',
                [$classId, $teacherId, $moduleId, $level, $endsAt]
            );
        }
        Response::ok(['id' => (int)$db->lastInsertId()]);
    }

    if ($action === 'stop') {
        $assignmentId = (int)($body['assignmentId'] ?? 0);
        if (!$assignmentId) Response::error('assignmentId erforderlich');
        // Zugehörige Klasse+Modul holen (für die class_modules-Bereinigung)
        $row = $db->fetchOne(
            'SELECT class_id, module_id FROM class_assignments WHERE id = ? AND teacher_id = ?',
            [$assignmentId, $teacherId]
        );
        $db->execute(
            'UPDATE class_assignments SET active = 0, ends_at = NOW() WHERE id = ? AND teacher_id = ?',
            [$assignmentId, $teacherId]
        );
        // Auftrag beenden = class_modules aus 'teacher_started' zurück auf 'free',
        // sonst sieht die Schüler-Ansicht (liest class_modules) die Aufgabe weiter.
        if ($row) {
            $db->execute(
                "UPDATE class_modules SET mode = 'free', paused = 0, started_at = NULL
                  WHERE class_id = ? AND module_id = ? AND mode = 'teacher_started'",
                [(int)$row['class_id'], $row['module_id']]
            );
        }
        Response::ok();
    }

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

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