<?php
require_once '../include/init.php';
require_once '../include/auth.php';

// --- Security Check: Only Admin can access this API ---
if (!isAdmin()) {
    http_response_code(403); // Forbidden
    echo json_encode(['error' => 'Permission denied.']);
    exit;
}

header('Content-Type: application/json');
$method = $_SERVER['REQUEST_METHOD'];
$response = [];

try {
    if ($method === 'GET') {
        $tab_id = filter_input(INPUT_GET, 'tab_id', FILTER_VALIDATE_INT);
        if ($tab_id) {
            $stmt = $pdo->prepare("SELECT user_id FROM tab_viewer_access WHERE tab_id = ?");
            $stmt->execute([$tab_id]);
            // Fetch just the user_id column into a simple array
            $response = $stmt->fetchAll(PDO::FETCH_COLUMN, 0); 
        } else {
            http_response_code(400); // Bad Request
            $response = ['error' => 'Tab ID is required.'];
        }
    } elseif ($method === 'POST') {
        $data = json_decode(file_get_contents('php://input'), true);
        $tab_id = $data['tab_id'] ?? null;
        $viewer_ids = $data['viewer_ids'] ?? [];

        if ($tab_id && is_array($viewer_ids)) {
            // Start transaction
            $pdo->beginTransaction();

            // 1. Delete existing entries for this tab
            $delete_stmt = $pdo->prepare("DELETE FROM tab_viewer_access WHERE tab_id = ?");
            $delete_stmt->execute([$tab_id]);

            // 2. Insert new entries
            if (!empty($viewer_ids)) {
                $insert_stmt = $pdo->prepare("INSERT INTO tab_viewer_access (tab_id, user_id) VALUES (?, ?)");
                foreach ($viewer_ids as $user_id) {
                    $insert_stmt->execute([$tab_id, $user_id]);
                }
            }
            
            // Commit transaction
            $pdo->commit();
            $response = ['success' => true];
        } else {
            http_response_code(400); // Bad Request
            $response = ['error' => 'Tab ID and a list of viewer IDs are required.'];
        }
    } else {
        http_response_code(405); // Method Not Allowed
        $response = ['error' => 'Method not allowed'];
    }
} catch (PDOException $e) {
    if ($pdo->inTransaction()) {
        $pdo->rollBack();
    }
    http_response_code(500); // Internal Server Error
    $response = ['error' => 'Database error: ' . $e->getMessage()];
}

echo json_encode($response);