<?php
    if ($_SERVER['HTTP_REFERER'] == "http://what-ch.mooo.com/test-php/dark.php") {
        header('Location: http://what-ch.mooo.com/test-php/dark.php');
    } else {
        header('Location: http://what-ch.mooo.com/test-php/index.php');
    }

    $post = $_POST['content'];
    $post = htmlspecialchars($post);
    $post = filter_var($post, FILTER_SANITIZE_STRING, FILTER_FLAG_STRIP_HIGH);

    if ($post !== "" && strlen($post) <= 200) {
        file_put_contents("content.txt", $post . "\n" . file_get_contents("content.txt"));
    }
?>