[鹤城杯 2021]EasyP

<?php
include "utils.php";

if (isset($_POST["guess"])) {
    $guess = (string) $_POST["guess"];
    if ($guess === $secret) {
        $message = "Congratulations! The flag is: " . $flag;
    } else {
        $message = "Wrong. Try Again";
    }
}

if (preg_match("/utils.php/*$/i", $_SERVER["PHP_SELF"])) {
    exit("hacker :)");
}

if (preg_match("/show_source/", $_SERVER["REQUEST_URI"])){
    exit("hacker :)");
}

if (isset($_GET["show_source"])) {
    highlight_file(basename($_SERVER["PHP_SELF"]));
    exit();
}else{
    show_source(__FILE__);
}
?>