edit_message.php

<?php
session_start();
include 'includes/db_connect.php';

if (!isset($_SESSION['user_id'])) {
    die("unauthorized");
}

if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_POST['message_id'], $_POST['new_message'])) {
    $message_id = intval($_POST['message_id']);
    $new_message = trim($_POST['new_message']);
    $user_id = $_SESSION['user_id'];

    $stmt = $conn->prepare("SELECT sender_id FROM chat_messages WHERE id = ?");
    $stmt->bind_param("i", $message_id);
    $stmt->execute();
    $msg = $stmt->get_result()->fetch_assoc();
    $stmt->close();

    if ($msg && $msg['sender_id'] == $user_id) {
        $update = $conn->prepare("UPDATE chat_messages SET message = ? WHERE id = ?");
        $update->bind_param("si", $new_message, $message_id);
        $update->execute();
        $update->close();
        echo "success";
    } else {
        echo "unauthorized";
    }
}
?>