<?php
/**
 * AJAX API voor Dagplanning & Taken
 */

require_once __DIR__ . '/../includes/auth.php';
require_once __DIR__ . '/../includes/settings.php';
require_once __DIR__ . '/../includes/integrations/microsoft.php';
$user = require_auth(true);
$db = get_db_connection();

header('Content-Type: application/json');

$action = $_GET['action'] ?? ($_POST['action'] ?? '');
$today = date('Y-m-d');

try {
    // 1. Dagdoel of notities opslaan
    if ($action === 'save_goal') {
        $data = json_decode(file_get_contents('php://input'), true);
        $date = $data['date'] ?? $today;
        $focusGoal = $data['focus_goal'] ?? '';
        $notes = $data['notes'] ?? '';

        $stmt = $db->prepare("
            INSERT INTO daily_plans (user_id, plan_date, focus_goal, notes)
            VALUES (?, ?, ?, ?)
            ON DUPLICATE KEY UPDATE focus_goal = VALUES(focus_goal), notes = VALUES(notes)
        ");
        $stmt->execute([$user['id'], $date, $focusGoal, $notes]);

        echo json_encode(['success' => true]);
        exit;
    }

    // 1b. Widget layout opslaan
    if ($action === 'save_widget_layout') {
        $data = json_decode(file_get_contents('php://input'), true);
        $layout = $data['layout'] ?? null;

        if (!is_array($layout)) {
            echo json_encode(['success' => false, 'error' => 'Ongeldig layout formaat']);
            exit;
        }

        // Valideer en sanitize layout items inclusief optionele custom widget titel
        $cleanedLayout = [];
        foreach ($layout as $item) {
            if (!is_array($item) || empty($item['id'])) continue;
            $cleaned = [
                'id'       => substr(trim((string)$item['id']), 0, 64),
                'enabled'  => !empty($item['enabled']),
                'col_span' => in_array((int)($item['col_span'] ?? 6), [4, 5, 6, 7, 8, 12]) ? (int)$item['col_span'] : 6,
                'order'    => (int)($item['order'] ?? 1),
            ];
            if (!empty($item['custom_title'])) {
                $customTitle = trim(strip_tags((string)$item['custom_title']));
                if ($customTitle !== '') {
                    $cleaned['custom_title'] = substr($customTitle, 0, 50);
                }
            }
            $cleanedLayout[] = $cleaned;
        }

        $stmt = $db->prepare("UPDATE users SET fociz_widget_layout = ? WHERE id = ?");
        $stmt->execute([json_encode($cleanedLayout, JSON_UNESCAPED_UNICODE), $user['id']]);

        echo json_encode(['success' => true, 'message' => 'Widget indeling succesvol opgeslagen']);
        exit;
    }

    // 1c. Scratchpad snelle notities opslaan
    if ($action === 'save_scratchpad') {
        $data = json_decode(file_get_contents('php://input'), true);
        $date = $data['date'] ?? $today;
        $notes = $data['notes'] ?? '';

        $stmt = $db->prepare("
            INSERT INTO daily_plans (user_id, plan_date, notes)
            VALUES (?, ?, ?)
            ON DUPLICATE KEY UPDATE notes = VALUES(notes)
        ");
        $stmt->execute([$user['id'], $date, $notes]);

        echo json_encode(['success' => true]);
        exit;
    }

    // 2. Taak toevoegen
    if ($action === 'add_task') {
        $data = json_decode(file_get_contents('php://input'), true);
        $title = trim($data['title'] ?? '');
        $priority = in_array($data['priority'] ?? '', ['P1', 'P2', 'P3']) ? $data['priority'] : 'P2';
        $timeBlockStart = !empty($data['time_block_start']) ? trim($data['time_block_start']) : null;
        $timeBlockEnd = !empty($data['time_block_end']) ? trim($data['time_block_end']) : null;
        $durationMinutes = (int)($data['duration_minutes'] ?? 0);
        $date = !empty($data['date']) ? trim($data['date']) : $today;
        $syncOutlook = !empty($data['sync_to_outlook']);

        if (empty($title)) {
            echo json_encode(['error' => 'Titel is verplicht']);
            exit;
        }

        // Als zowel start- als eindtijd zijn opgegeven, bereken exact de minuten
        if (!empty($timeBlockStart) && !empty($timeBlockEnd)) {
            $t1 = strtotime("2000-01-01 {$timeBlockStart}");
            $t2 = strtotime("2000-01-01 {$timeBlockEnd}");
            if ($t1 !== false && $t2 !== false && $t2 > $t1) {
                $durationMinutes = (int)(($t2 - $t1) / 60);
            }
        }

        if ($durationMinutes <= 0) {
            $durationMinutes = 30;
        }

        // Als starttijd bekend is maar eindtijd nog niet, bereken eindtijd
        if (!empty($timeBlockStart) && empty($timeBlockEnd)) {
            try {
                $dtEnd = new DateTime("{$date} {$timeBlockStart}:00", new DateTimeZone('Europe/Amsterdam'));
                $dtEnd->modify("+{$durationMinutes} minutes");
                $timeBlockEnd = $dtEnd->format('H:i');
            } catch (Throwable $e) {
                // negeer
            }
        }
        // Haal of maak daily plan op
        $stmtPlan = $db->prepare("
            INSERT INTO daily_plans (user_id, plan_date)
            VALUES (?, ?)
            ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id)
        ");
        $stmtPlan->execute([$user['id'], $date]);
        $planId = $db->lastInsertId();

        $source = !empty($data['source']) ? substr(trim($data['source']), 0, 50) : 'FOCIZ';
        $externalId = !empty($data['external_id']) ? substr(trim($data['external_id']), 0, 255) : null;
        $externalUrl = !empty($data['external_url']) ? trim($data['external_url']) : null;
        $outlookSyncError = null;

        // Als synchronisatie naar Outlook gewenst is (of source is OUTLOOK) en nog geen extern ID heeft
        if (($syncOutlook || $source === 'OUTLOOK') && empty($externalId)) {
            // Als er geen starttijd is ingevuld maar wel sync gewenst is, gebruik 09:00 als veilige standaard
            if (empty($timeBlockStart)) {
                $timeBlockStart = '09:00';
            }

            $msResult = microsoft_create_event($user['id'], [
                'subject'          => $title,
                'description'      => "Gepland via Fociz Dagplanning ({$priority})",
                'date'             => $date,
                'start_time'       => $timeBlockStart,
                'end_time'         => $timeBlockEnd,
                'duration_minutes' => $durationMinutes,
            ]);

            if (!empty($msResult['success']) && !empty($msResult['event_id'])) {
                $source = 'OUTLOOK';
                $externalId = $msResult['event_id'];
                $externalUrl = $msResult['web_link'] ?? 'https://outlook.office.com';
                $timeBlockStart = $msResult['start_time'] ?? $timeBlockStart;
                $timeBlockEnd = $msResult['end_time'] ?? $timeBlockEnd;
            } else {
                $outlookSyncError = $msResult['error'] ?? 'Kon afspraak niet aanmaken in Microsoft Outlook';
            }
        }
        $stmt = $db->prepare("
            INSERT INTO tasks (user_id, daily_plan_id, title, priority, time_block_start, time_block_end, duration_minutes, status, source, external_id, external_url)
            VALUES (?, ?, ?, ?, ?, ?, ?, 'TODO', ?, ?, ?)
        ");
        $stmt->execute([$user['id'], $planId, $title, $priority, $timeBlockStart, $timeBlockEnd, $durationMinutes, $source, $externalId, $externalUrl]);
        $taskId = (int)$db->lastInsertId();

        echo json_encode([
            'success' => true,
            'task' => [
                'id' => $taskId,
                'title' => $title,
                'priority' => $priority,
                'time_block_start' => $timeBlockStart,
                'time_block_end' => $timeBlockEnd,
                'duration_minutes' => $durationMinutes,
                'is_completed' => 0,
                'status' => 'TODO',
                'source' => $source,
                'external_id' => $externalId,
                'external_url' => $externalUrl,
            ],
            'outlook_synced' => ($source === 'OUTLOOK' && !empty($externalId)),
            'outlook_error' => $outlookSyncError,
        ]);
        exit;
    }

    // 2b. Taak bewerken (titel, prioriteit, starttijd, eindtijd, duur)
    if ($action === 'update_task') {
        $data = json_decode(file_get_contents('php://input'), true);
        $taskId = (int)($data['task_id'] ?? 0);
        $title = trim($data['title'] ?? '');
        $priority = in_array($data['priority'] ?? '', ['P1', 'P2', 'P3']) ? $data['priority'] : 'P2';
        $timeBlockStart = !empty($data['time_block_start']) ? trim($data['time_block_start']) : null;
        $timeBlockEnd = !empty($data['time_block_end']) ? trim($data['time_block_end']) : null;
        $durationMinutes = (int)($data['duration_minutes'] ?? 0);

        if (empty($title)) {
            echo json_encode(['error' => 'Titel mag niet leeg zijn']);
            exit;
        }

        // Haal bestaande taak op
        $stmtTask = $db->prepare("SELECT * FROM tasks WHERE id = ? AND user_id = ?");
        $stmtTask->execute([$taskId, $user['id']]);
        $existingTask = $stmtTask->fetch();

        if (!$existingTask) {
            echo json_encode(['error' => 'Taak niet gevonden']);
            exit;
        }

        if (!empty($timeBlockStart) && !empty($timeBlockEnd)) {
            $t1 = strtotime("2000-01-01 {$timeBlockStart}");
            $t2 = strtotime("2000-01-01 {$timeBlockEnd}");
            if ($t1 !== false && $t2 !== false && $t2 > $t1) {
                $durationMinutes = (int)(($t2 - $t1) / 60);
            }
        }

        if ($durationMinutes <= 0) {
            $durationMinutes = (int)($existingTask['duration_minutes'] ?: 30);
        }

        if (!empty($timeBlockStart) && empty($timeBlockEnd)) {
            try {
                $dtEnd = new DateTime("2000-01-01 {$timeBlockStart}:00", new DateTimeZone('Europe/Amsterdam'));
                $dtEnd->modify("+{$durationMinutes} minutes");
                $timeBlockEnd = $dtEnd->format('H:i');
            } catch (Throwable $e) {}
        }

        $targetDate = !empty($data['date']) ? trim($data['date']) : null;
        $planDate = null;
        $newPlanId = null;

        if ($targetDate && preg_match('/^\d{4}-\d{2}-\d{2}$/', $targetDate)) {
            $stmtPlan = $db->prepare("
                INSERT INTO daily_plans (user_id, plan_date)
                VALUES (?, ?)
                ON DUPLICATE KEY UPDATE id=LAST_INSERT_ID(id)
            ");
            $stmtPlan->execute([$user['id'], $targetDate]);
            $newPlanId = (int)$db->lastInsertId();
            $planDate = $targetDate;
        } else {
            $stmtPlan = $db->prepare("SELECT plan_date FROM daily_plans WHERE id = ?");
            $stmtPlan->execute([$existingTask['daily_plan_id']]);
            $planDate = $stmtPlan->fetchColumn() ?: date('Y-m-d');
        }

        // Indien gekoppeld aan Outlook, werk afspraak bij via Graph API
        if (!empty($existingTask['external_id']) && $existingTask['source'] === 'OUTLOOK') {
            try {
                microsoft_update_event($user['id'], $existingTask['external_id'], [
                    'subject'    => $title,
                    'date'       => $planDate,
                    'start_time' => $timeBlockStart ?: '09:00',
                    'end_time'   => $timeBlockEnd ?: '09:30',
                ]);
            } catch (Throwable $t) {
                error_log("Fout bij bijwerken Outlook event: " . $t->getMessage());
            }
        }

        if ($newPlanId) {
            $stmtUpdate = $db->prepare("
                UPDATE tasks 
                SET title = ?, priority = ?, time_block_start = ?, time_block_end = ?, duration_minutes = ?, daily_plan_id = ?
                WHERE id = ? AND user_id = ?
            ");
            $stmtUpdate->execute([$title, $priority, $timeBlockStart, $timeBlockEnd, $durationMinutes, $newPlanId, $taskId, $user['id']]);
        } else {
            $stmtUpdate = $db->prepare("
                UPDATE tasks 
                SET title = ?, priority = ?, time_block_start = ?, time_block_end = ?, duration_minutes = ?
                WHERE id = ? AND user_id = ?
            ");
            $stmtUpdate->execute([$title, $priority, $timeBlockStart, $timeBlockEnd, $durationMinutes, $taskId, $user['id']]);
        }

        echo json_encode([
            'success' => true,
            'time_block_start' => $timeBlockStart,
            'time_block_end' => $timeBlockEnd,
            'duration_minutes' => $durationMinutes,
            'date' => $planDate
        ]);
        exit;
    }

    // 3. Bestaande taak handmatig naar Microsoft Outlook synchroniseren
    if ($action === 'sync_task_to_outlook') {
        $data = json_decode(file_get_contents('php://input'), true);
        $taskId = (int)($data['task_id'] ?? 0);

        if (!$taskId) {
            echo json_encode(['error' => 'Geen taak-ID opgegeven']);
            exit;
        }

        // Haal taak inclusief plan datum op
        $stmtTask = $db->prepare("
            SELECT t.*, dp.plan_date
            FROM tasks t
            LEFT JOIN daily_plans dp ON t.daily_plan_id = dp.id
            WHERE t.id = ? AND t.user_id = ?
        ");
        $stmtTask->execute([$taskId, $user['id']]);
        $task = $stmtTask->fetch();

        if (!$task) {
            echo json_encode(['error' => 'Taak niet gevonden']);
            exit;
        }

        // Als al gesynchroniseerd
        if (!empty($task['external_id']) && $task['source'] === 'OUTLOOK') {
            echo json_encode([
                'success' => true,
                'already_synced' => true,
                'external_id' => $task['external_id'],
                'external_url' => $task['external_url']
            ]);
            exit;
        }

        $planDate = $task['plan_date'] ?: $today;
        $startTime = !empty($task['time_block_start']) ? $task['time_block_start'] : ($data['time_block_start'] ?? '09:00');
        $endTime = !empty($task['time_block_end']) ? $task['time_block_end'] : null;
        $duration = (int)($task['duration_minutes'] ?: 30);

        $msResult = microsoft_create_event($user['id'], [
            'subject'          => $task['title'],
            'description'      => "Gepland via Fociz Dagplanning (" . $task['priority'] . ")",
            'date'             => $planDate,
            'start_time'       => $startTime,
            'end_time'         => $endTime,
            'duration_minutes' => $duration,
        ]);

        if (empty($msResult['success']) || empty($msResult['event_id'])) {
            echo json_encode(['error' => $msResult['error'] ?? 'Kon afspraak niet aanmaken in Microsoft Outlook']);
            exit;
        }

        // Sla Outlook ID en bron op in de taak
        $stmtUp = $db->prepare("
            UPDATE tasks 
            SET source = 'OUTLOOK', 
                external_id = ?, 
                external_url = ?, 
                time_block_start = COALESCE(time_block_start, ?),
                time_block_end = ?
            WHERE id = ? AND user_id = ?
        ");
        $stmtUp->execute([
            $msResult['event_id'],
            $msResult['web_link'] ?? 'https://outlook.office.com',
            $msResult['start_time'],
            $msResult['end_time'],
            $taskId,
            $user['id']
        ]);

        echo json_encode([
            'success' => true,
            'external_id' => $msResult['event_id'],
            'external_url' => $msResult['web_link'] ?? 'https://outlook.office.com',
            'start_time' => $msResult['start_time'],
            'end_time' => $msResult['end_time'],
        ]);
        exit;
    }

    // 4. Taak status toggelen (voltooid / open)
    if ($action === 'toggle_task') {
        $data = json_decode(file_get_contents('php://input'), true);
        $taskId = (int)($data['task_id'] ?? 0);
        $isCompleted = !empty($data['is_completed']) ? 1 : 0;
        $status = $isCompleted ? 'DONE' : 'TODO';

        $stmt = $db->prepare("
            UPDATE tasks SET is_completed = ?, status = ?
            WHERE id = ? AND user_id = ?
        ");
        $stmt->execute([$isCompleted, $status, $taskId, $user['id']]);

        echo json_encode(['success' => true]);
        exit;
    }

    // 5. Taak verwijderen (verwijder ook eventueel gekoppelde Outlook afspraak)
    if ($action === 'delete_task') {
        $data = json_decode(file_get_contents('php://input'), true);
        $taskId = (int)($data['task_id'] ?? 0);

        // Haal eerst op of deze taak aan Outlook was gekoppeld
        $stmtCheck = $db->prepare("SELECT external_id, source FROM tasks WHERE id = ? AND user_id = ?");
        $stmtCheck->execute([$taskId, $user['id']]);
        $taskToDelete = $stmtCheck->fetch();

        if ($taskToDelete && !empty($taskToDelete['external_id']) && $taskToDelete['source'] === 'OUTLOOK') {
            try {
                microsoft_delete_event($user['id'], $taskToDelete['external_id']);
            } catch (Throwable $t) {
                error_log("Fout bij verwijderen Outlook afspraak voor taak {$taskId}: " . $t->getMessage());
            }
        }

        $stmt = $db->prepare("DELETE FROM tasks WHERE id = ? AND user_id = ?");
        $stmt->execute([$taskId, $user['id']]);

        echo json_encode(['success' => true]);
        exit;
    }

    // 6. Realtime Outlook synchronisatie & controle op gewijzigde/gewiste items
    if ($action === 'check_outlook_sync') {
        $rawInput = file_get_contents('php://input');
        $data = !empty($rawInput) ? (json_decode($rawInput, true) ?: []) : [];
        if (empty($data)) {
            $data = $_GET;
        }

        $planDate = !empty($data['plan_date']) ? trim($data['plan_date']) : $today;
        $weekStart = !empty($data['week_start']) ? trim($data['week_start']) : date('Y-m-d', strtotime('monday this week', strtotime($planDate)));
        $weekEnd = !empty($data['week_end']) ? trim($data['week_end']) : date('Y-m-d', strtotime('sunday this week', strtotime($planDate)));
        $lastHash = !empty($data['last_hash']) ? trim($data['last_hash']) : '';

        // Controleer of Outlook gekoppeld is
        $stmtInt = $db->prepare("SELECT * FROM integrations WHERE user_id = ? AND provider = 'OUTLOOK' AND is_enabled = 1");
        $stmtInt->execute([$user['id']]);
        $integration = $stmtInt->fetch();

        if (!$integration || empty($integration['access_token']) || !empty($integration['is_demo_mode'])) {
            echo json_encode([
                'success'     => true,
                'connected'   => false,
                'has_changes' => false,
                'last_sync'   => date('H:i:s'),
            ]);
            exit;
        }

        // Haal live afspraken op voor de hele week
        $weekLiveEvents = microsoft_fetch_events_range($user['id'], $weekStart, $weekEnd);

        // Voer reconciliatie uit met de Fociz tasks tabel
        $reconcileRes = microsoft_reconcile_tasks_with_outlook($user['id'], $weekStart, $weekEnd, $weekLiveEvents);

        // Haal de geactualiseerde taken voor deze dag op
        $stmtPlan = $db->prepare("SELECT id FROM daily_plans WHERE user_id = ? AND plan_date = ?");
        $stmtPlan->execute([$user['id'], $planDate]);
        $planId = $stmtPlan->fetchColumn();

        $tasks = [];
        if ($planId) {
            $stmtTasks = $db->prepare("
                SELECT id, title, priority, time_block_start, time_block_end, duration_minutes, is_completed, status, source, external_id
                FROM tasks
                WHERE user_id = ? AND (daily_plan_id = ? " . ($planDate === $today ? "OR daily_plan_id IS NULL" : "") . ")
                ORDER BY is_completed ASC, priority ASC, time_block_start ASC, created_at DESC
            ");
            $stmtTasks->execute([$user['id'], $planId]);
            $tasks = $stmtTasks->fetchAll();
        }

        // Filter events voor de geselecteerde dag die geen gesynchroniseerde Fociz taak zijn
        $syncedIds = [];
        foreach ($tasks as $t) {
            if (!empty($t['external_id'])) {
                $syncedIds[$t['external_id']] = true;
            }
        }

        $dayEvents = [];
        foreach ($weekLiveEvents as $e) {
            if (($e['date'] ?? '') === $planDate) {
                if (!empty($e['id']) && isset($syncedIds[$e['id']])) {
                    continue;
                }
                $dayEvents[] = [
                    'id'      => $e['id'],
                    'start'   => $e['start'],
                    'end'     => $e['end'],
                    'subject' => $e['subject'],
                ];
            }
        }

        // Bereken status hash voor de dag
        $hashData = [
            'events' => $dayEvents,
            'tasks'  => array_map(function($t) {
                return [
                    'id'               => $t['id'],
                    'title'            => $t['title'],
                    'time_block_start' => $t['time_block_start'],
                    'time_block_end'   => $t['time_block_end'],
                    'is_completed'     => $t['is_completed'],
                ];
            }, $tasks)
        ];
        $currentHash = md5(json_encode($hashData));

        $hasChanges = ($reconcileRes['deleted'] > 0 || $reconcileRes['updated'] > 0);
        if (!empty($lastHash) && $lastHash !== $currentHash) {
            $hasChanges = true;
        }

        echo json_encode([
            'success'       => true,
            'connected'     => true,
            'has_changes'   => $hasChanges,
            'hash'          => $currentHash,
            'deleted_count' => $reconcileRes['deleted'],
            'updated_count' => $reconcileRes['updated'],
            'events_count'  => count($dayEvents),
            'tasks_count'   => count($tasks),
            'last_sync'     => date('H:i:s'),
        ]);
        exit;
    }

    // --- V2.0: Subtaken & Checklists ---

    // 7. Subtaak toevoegen aan een taak
    if ($action === 'add_subtask') {
        $data = json_decode(file_get_contents('php://input'), true);
        $taskId = (int)($data['task_id'] ?? 0);
        $title  = trim($data['title'] ?? '');

        if (!$taskId || empty($title)) {
            echo json_encode(['error' => 'Taak-ID en titel zijn verplicht']);
            exit;
        }

        // Controleer of de taak van deze gebruiker is
        $stmtCheck = $db->prepare("SELECT id FROM tasks WHERE id = ? AND user_id = ?");
        $stmtCheck->execute([$taskId, $user['id']]);
        if (!$stmtCheck->fetchColumn()) {
            echo json_encode(['error' => 'Taak niet gevonden']);
            exit;
        }

        // Bereken positie (achteraan)
        $stmtPos = $db->prepare("SELECT COALESCE(MAX(position), -1) + 1 FROM task_subtasks WHERE task_id = ?");
        $stmtPos->execute([$taskId]);
        $position = (int)$stmtPos->fetchColumn();

        $stmt = $db->prepare("
            INSERT INTO task_subtasks (task_id, user_id, title, is_completed, position)
            VALUES (?, ?, ?, 0, ?)
        ");
        $stmt->execute([$taskId, $user['id'], substr($title, 0, 255), $position]);
        $subtaskId = (int)$db->lastInsertId();

        echo json_encode([
            'success'  => true,
            'subtask'  => [
                'id'           => $subtaskId,
                'task_id'      => $taskId,
                'title'        => $title,
                'is_completed' => 0,
                'position'     => $position,
            ]
        ]);
        exit;
    }

    // 8. Subtaak afvinken / openzetten
    if ($action === 'toggle_subtask') {
        $data = json_decode(file_get_contents('php://input'), true);
        $subtaskId   = (int)($data['subtask_id'] ?? 0);
        $isCompleted = !empty($data['is_completed']) ? 1 : 0;

        if (!$subtaskId) {
            echo json_encode(['error' => 'Subtaak-ID ontbreekt']);
            exit;
        }

        $stmt = $db->prepare("
            UPDATE task_subtasks SET is_completed = ?
            WHERE id = ? AND user_id = ?
        ");
        $stmt->execute([$isCompleted, $subtaskId, $user['id']]);

        echo json_encode(['success' => true, 'is_completed' => $isCompleted]);
        exit;
    }

    // 9. Subtaak verwijderen
    if ($action === 'delete_subtask') {
        $data = json_decode(file_get_contents('php://input'), true);
        $subtaskId = (int)($data['subtask_id'] ?? 0);

        if (!$subtaskId) {
            echo json_encode(['error' => 'Subtaak-ID ontbreekt']);
            exit;
        }

        $stmt = $db->prepare("DELETE FROM task_subtasks WHERE id = ? AND user_id = ?");
        $stmt->execute([$subtaskId, $user['id']]);

        echo json_encode(['success' => true]);
        exit;
    }

    // 10. Subtaken ophalen voor een taak
    if ($action === 'get_subtasks') {
        $taskId = (int)($_GET['task_id'] ?? 0);

        if (!$taskId) {
            echo json_encode(['error' => 'Taak-ID ontbreekt']);
            exit;
        }

        // Controleer eigenaarschap
        $stmtCheck = $db->prepare("SELECT id FROM tasks WHERE id = ? AND user_id = ?");
        $stmtCheck->execute([$taskId, $user['id']]);
        if (!$stmtCheck->fetchColumn()) {
            echo json_encode(['error' => 'Taak niet gevonden']);
            exit;
        }

        $stmt = $db->prepare("
            SELECT id, task_id, title, is_completed, position
            FROM task_subtasks
            WHERE task_id = ? AND user_id = ?
            ORDER BY position ASC, created_at ASC
        ");
        $stmt->execute([$taskId, $user['id']]);
        $subtasks = $stmt->fetchAll();

        echo json_encode(['success' => true, 'subtasks' => $subtasks]);
        exit;
    }

    // 11. Zoek eerstvolgende vrije open blok binnen werktijden (Release v2.1)
    if ($action === 'find_next_free_slot') {
        $rawInput = json_decode(file_get_contents('php://input'), true);
        $data = is_array($rawInput) ? $rawInput : $_GET;
        $duration = max(5, (int)($data['duration_minutes'] ?? 30));
        $excludeTaskId = (int)($data['task_id'] ?? 0);
        $startFromNextWorkday = !empty($data['start_from_next_workday']);

        $workdaySettings = get_workday_settings();
        $workdayStartStr = $workdaySettings['workday_start'] ?? '08:30';
        $workdayEndStr   = $workdaySettings['workday_end'] ?? '17:00';
        $lunchStartStr   = $workdaySettings['lunch_start'] ?? '12:30';
        $lunchEndStr     = $workdaySettings['lunch_end'] ?? '13:00';

        $toMins = function(string $timeStr): int {
            $parts = explode(':', trim($timeStr));
            return ((int)($parts[0] ?? 0) * 60) + (int)($parts[1] ?? 0);
        };

        $toTimeStr = function(int $mins): string {
            $h = (int)floor($mins / 60);
            $m = $mins % 60;
            return sprintf('%02d:%02d', $h, $m);
        };

        $workdayStartMin = $toMins($workdayStartStr);
        $workdayEndMin   = $toMins($workdayEndStr);
        $lunchStartMin   = $toMins($lunchStartStr);
        $lunchEndMin     = $toMins($lunchEndStr);

        $tz = new DateTimeZone('Europe/Amsterdam');
        $now = new DateTime('now', $tz);

        // Huidige tijd afronden naar hele kwartieren
        $nowH = (int)$now->format('G');
        $nowM = (int)$now->format('i');
        if ($nowM % 15 !== 0) {
            $nowM = (int)(ceil($nowM / 15) * 15);
            if ($nowM >= 60) {
                $nowH += (int)floor($nowM / 60);
                $nowM = $nowM % 60;
            }
        }
        $currentQuarterMin = $nowH * 60 + $nowM;

        $dutchDays = [1 => 'Maandag', 2 => 'Dinsdag', 3 => 'Woensdag', 4 => 'Donderdag', 5 => 'Vrijdag', 6 => 'Zaterdag', 7 => 'Zondag'];
        $dutchMonths = ['', 'jan', 'feb', 'mrt', 'apr', 'mei', 'jun', 'jul', 'aug', 'sep', 'okt', 'nov', 'dec'];

        $checkDate = clone $now;
        if ($startFromNextWorkday) {
            $checkDate->modify('+1 day');
            while ((int)$checkDate->format('N') >= 6) {
                $checkDate->modify('+1 day');
            }
        }
        $foundSlot = null;
        $maxDays = 14;
        $checkedDays = 0;

        // Bepaal het totale zoekvenster voor batch-ophalen (O(1) database & Graph API schaalbaarheid)
        $rangeStartDate = $checkDate->format('Y-m-d');
        $rangeEndObj = clone $checkDate;
        $rangeEndObj->modify('+21 days'); // ruim venster incl. weekenden
        $rangeEndDate = $rangeEndObj->format('Y-m-d');

        // 1. Batch SQL: haal alle bestaande taken van de gebruiker in 1 geoptimaliseerde query op
        $tasksByDate = [];
        $stmtTasks = $db->prepare("
            SELECT t.id, dp.plan_date, t.time_block_start, t.time_block_end, t.duration_minutes 
            FROM tasks t
            INNER JOIN daily_plans dp ON t.daily_plan_id = dp.id
            WHERE t.user_id = ? 
              AND dp.plan_date BETWEEN ? AND ?
              AND t.time_block_start IS NOT NULL 
              AND t.time_block_start != ''
              AND t.status != 'CANCELLED'
        ");
        $stmtTasks->execute([$user['id'], $rangeStartDate, $rangeEndDate]);
        while ($t = $stmtTasks->fetch()) {
            if ($excludeTaskId > 0 && (int)$t['id'] === $excludeTaskId) {
                continue;
            }
            $tasksByDate[$t['plan_date']][] = $t;
        }

        // 2. Batch Microsoft Graph: haal alle Outlook events in 1 API call op voor het gehele venster
        $outlookByDate = [];
        if (function_exists('microsoft_fetch_events_range')) {
            try {
                $allOutlookEvts = microsoft_fetch_events_range($user['id'], $rangeStartDate, $rangeEndDate, false);
                foreach ($allOutlookEvts as $oe) {
                    if (!empty($oe['date'])) {
                        $outlookByDate[$oe['date']][] = $oe;
                    }
                }
            } catch (Throwable $e) {}
        }

        while ($checkedDays < $maxDays) {
            $dayOfWeek = (int)$checkDate->format('N'); // 1 = Ma, 7 = Zo

            // Weekend overslaan
            if ($dayOfWeek === 6 || $dayOfWeek === 7) {
                $checkDate->modify('+1 day');
                continue;
            }

            $dateStr = $checkDate->format('Y-m-d');
            $isToday = ($dateStr === $now->format('Y-m-d')) && !$startFromNextWorkday;

            // Bepaal vroegste startminuut voor deze dag (op hele kwartieren)
            if ($isToday) {
                $earliestMin = max($workdayStartMin, $currentQuarterMin);
                if ($earliestMin % 15 !== 0) {
                    $earliestMin = (int)(ceil($earliestMin / 15) * 15);
                }
            } else {
                $earliestMin = $workdayStartMin;
                if ($earliestMin % 15 !== 0) {
                    $earliestMin = (int)(ceil($earliestMin / 15) * 15);
                }
            }

            // Alleen zoeken als er binnen de werkdag nog voldoende tijd is voor duration
            if ($earliestMin + $duration <= $workdayEndMin) {
                $busyIntervals = [];

                // Lunchpauze
                if ($lunchEndMin > $lunchStartMin) {
                    $busyIntervals[] = [$lunchStartMin, $lunchEndMin];
                }

                // Bestaande taken voor deze datum uit het geheugen
                $dayTasks = $tasksByDate[$dateStr] ?? [];
                foreach ($dayTasks as $t) {
                    $tStart = $toMins($t['time_block_start']);
                    $tDur = (int)($t['duration_minutes'] ?: 30);
                    $tEnd = !empty($t['time_block_end']) ? $toMins($t['time_block_end']) : ($tStart + $tDur);
                    if ($tEnd > $tStart) {
                        $busyIntervals[] = [$tStart, $tEnd];
                    }
                }

                // Outlook afspraken voor deze datum uit het geheugen
                $dayOutlook = $outlookByDate[$dateStr] ?? [];
                foreach ($dayOutlook as $oe) {
                    if (!empty($oe['is_all_day'])) continue;
                    if (empty($oe['start']) || empty($oe['end'])) continue;
                    $oStart = $toMins($oe['start']);
                    $oEnd = $toMins($oe['end']);
                    if ($oEnd > $oStart) {
                        $busyIntervals[] = [$oStart, $oEnd];
                    }
                }

                // Doorzoek kwartierslots
                for ($slotStart = $earliestMin; ($slotStart + $duration) <= $workdayEndMin; $slotStart += 15) {
                    $slotEnd = $slotStart + $duration;
                    $hasCollision = false;

                    foreach ($busyIntervals as [$bStart, $bEnd]) {
                        if ($slotStart < $bEnd && $slotEnd > $bStart) {
                            $hasCollision = true;
                            break;
                        }
                    }

                    if (!$hasCollision) {
                        $foundSlot = [
                            'date'             => $dateStr,
                            'start'            => $toTimeStr($slotStart),
                            'end'              => $toTimeStr($slotEnd),
                            'duration_minutes' => $duration,
                            'is_today'         => $isToday,
                            'formatted_date'   => $isToday 
                                ? 'Vandaag (' . date('j', strtotime($dateStr)) . ' ' . $dutchMonths[(int)date('n', strtotime($dateStr))] . ')' 
                                : $dutchDays[(int)$checkDate->format('N')] . ' ' . date('j', strtotime($dateStr)) . ' ' . $dutchMonths[(int)date('n', strtotime($dateStr))],
                        ];
                        break 2;
                    }
                }
            }

            $checkDate->modify('+1 day');
            $checkedDays++;
        }

        if ($foundSlot) {
            echo json_encode([
                'success'       => true,
                'slot'          => $foundSlot,
                'workday_start' => $workdayStartStr,
                'workday_end'   => $workdayEndStr,
            ]);
        } else {
            echo json_encode([
                'success'       => false,
                'workday_start' => $workdayStartStr,
                'workday_end'   => $workdayEndStr,
                'error'         => "Geen vrij blok van {$duration} minuten gevonden binnen de gezette werktijden ({$workdayStartStr} - {$workdayEndStr}) voor de komende {$maxDays} werkdagen.",
            ]);
        }
        exit;
    }

    echo json_encode(['error' => 'Onbekende actie']);
} catch (Exception $e) {
    http_response_code(500);
    echo json_encode(['error' => $e->getMessage()]);
}