PHP chatroom

<?php session_start(); ob_start(); header("Content-type: application/json"); date_default_timezone_set('UTC'); //connect to database $db = mysqli_connect('localhost', 'micdim1_poll', 'Dallas@1997', 'micdim1_poll'); if (mysqli_connect_errno()) { echo '<p>Error: Could not connect to database.<br/> Please try again later.</p>'; exit; } try { $currentTime = time(); $session_id = session_id(); $lastPoll = isset($_SESSION['last_poll']) ? $_SESSION['last_poll'] : $currentTime; $action = isset($_SERVER['REQUEST_METHOD']) && ($_SERVER['REQUEST_METHOD'] == 'POST') ? 'send' : 'poll'; switch($action) { case 'poll': $query = "SELECT * FROM chatlog WHERE date_created >= ?"; $stmt = $db->prepare($query); $stmt->bind_param('s', $lastPoll); $stmt->execute(); $stmt->bind_result($id, $message, $session_id, $date_created); $result = $stmt->get_result(); $newChats = []; while($chat = $result->fetch_assoc()) { if($session_id == $chat['sent_by']) { $chat['sent_by'] = 'self'; } else { $chat['sent_by'] = 'other'; } $newChats[] = $chat; } $_SESSION['last_poll'] = $currentTime; print json_encode([ 'success' => true, 'messages' => $newChats ]); exit; case 'send': $message = isset($_POST['message']) ? $_POST['message'] : ''; $message = strip_tags($message); $query = "INSERT INTO chatlog (message, sent_by, date_created) VALUES(?, ?, ?)"; $stmt = $db->prepare($query); $stmt->bind_param('ssi', $message, $session_id, $currentTime); $stmt->execute(); print json_encode(['success' => true]); exit; } } catch(\Exception $e) { print json_encode([ 'success' => false, 'error' => $e->getMessage() ]); }