<?php
/**
 * GET /api/teacher/live-stream?classId=42
 *
 * Server-Sent Events für Lehrer-Live-Dashboard.
 * Pollt regelmäßig die telemetry_events_v2 nach neuen Events der Klasse
 * und sendet sie als SSE.
 *
 * NOTE: Apache nutzt häufig prefork und blockiert lange Connections.
 * Für Produktion ggf. auf Long-Polling oder Websocket umstellen.
 */

declare(strict_types=1);
require_once __DIR__ . '/../../bootstrap.php';

v2_validate_method('GET');
$auth = v2_auth_require('teacher');
$teacherId = (int) ($auth['sub'] ?? 0);
$classId = (int) ($_GET['classId'] ?? 0);
if (!$classId) {
    v2_response_error(400, 'missing_classId', 'Parameter "classId" fehlt.');
}

// Lehrer-Berechtigung für die Klasse prüfen
$ok = v2_db_one("
    SELECT id FROM classes WHERE id = :cid AND teacher_id = :tid
", [':cid' => $classId, ':tid' => $teacherId]);
if (!$ok) {
    v2_response_error(403, 'forbidden', 'Diese Klasse gehört nicht dieser Lehrperson.');
}

// SSE-Header
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache');
header('X-Accel-Buffering: no');
ob_implicit_flush(true);
@ob_end_flush();

$lastId = 0;
$startTs = time();

// Initial dump: letzte 30 Events der Klasse, falls Lehrperson mitten in Stunde reinhängt
$initial = v2_db_all("
    SELECT id, student_id, module_slug, event_type, phase, phase_label, step,
           current_score, score_max, time_in_phase_s, milestone_id, milestone_label,
           idle_s, hint, blocker_type, ts
    FROM telemetry_events_v2
    WHERE class_id = :cid AND ts > NOW() - INTERVAL 5 MINUTE
    ORDER BY id ASC
    LIMIT 30
", [':cid' => $classId]);
foreach ($initial as $row) {
    echo "id: {$row['id']}\n";
    echo "event: telemetry\n";
    echo 'data: ' . json_encode($row, JSON_UNESCAPED_UNICODE) . "\n\n";
    $lastId = max($lastId, (int) $row['id']);
}

// Loop — max 60s, dann Client-Reconnect
while (time() - $startTs < 60) {
    if (connection_aborted()) break;

    $rows = v2_db_all("
        SELECT id, student_id, module_slug, event_type, phase, phase_label, step,
               current_score, score_max, time_in_phase_s, milestone_id, milestone_label,
               idle_s, hint, blocker_type, ts
        FROM telemetry_events_v2
        WHERE class_id = :cid AND id > :lid
        ORDER BY id ASC
        LIMIT 50
    ", [':cid' => $classId, ':lid' => $lastId]);

    foreach ($rows as $row) {
        echo "id: {$row['id']}\n";
        echo "event: telemetry\n";
        echo 'data: ' . json_encode($row, JSON_UNESCAPED_UNICODE) . "\n\n";
        $lastId = (int) $row['id'];
    }

    // Heartbeat-Comment damit Verbindung nicht abreißt
    echo ": ping\n\n";
    @flush();
    sleep(2);
}