save_note.php

<?php
require_once '/home/chzruk/public_html/public/bootstrap.php';

if (!isset($_SESSION['user_id']) || !is_numeric($_SESSION['user_id'])) {
    http_response_code(403);
    exit("Not authenticated");
}

$user_id = (int)$_SESSION['user_id'];

$conn = new mysqli('', '', '', '');
if ($conn->connect_error) {
    http_response_code(500);
    exit("Connection failed");
}

if (!isset($_POST['content'])) {
    http_response_code(400);
    exit("No content");
}

$content = $_POST['content'];

// INSERT or UPDATE (requires UNIQUE INDEX on user_id)
$stmt = $conn->prepare("
    INSERT INTO note (user_id, content, updated_at)
    VALUES (?, ?, NOW())
    ON DUPLICATE KEY UPDATE
        content = ?,
        updated_at = NOW()
");

$stmt->bind_param("iss", $user_id, $content, $content);

$success = $stmt->execute();

echo $success ? "Note saved" : "Save failed";
$stmt->close();
$conn->close();