guestbook/submit.php

<?php
class data {
	public $name;
	public $message;
	public $date;
	public $mlength;
	public $nlength;
	function set_date() {
		$this->date = date("Y M d");
	}
	function set_mlength() {
		$this->mlength = strlen($this->message);
	}
	function set_nlength() {
		$this->nlength = strlen($this->name);
	}
}
$ndata = new data();




$name = $ndata->name =  htmlspecialchars($_POST["fname"]);
$message = $ndata->message = htmlspecialchars($_POST["fmessage"]);
$ndata->set_date();
$ndata->set_mlength();
$ndata->set_nlength();
$mlength = $ndata->mlength;
$nlength = $ndata->nlength;

# Setup JSON

$newURL = "https://" . $_SERVER['SERVER_NAME'] . "/guestbook/index.html";

# Check name and message
if ($name == "") {
  header('Refresh:2; url=' . $newURL );
  echo "There is no name, Try again with a name";
  exit();
}
if ($message == "") {
  header('Refresh:2; url=' . $newURL );
  echo "There is no message, Try again with a message";
  exit();
}
if($mlength > 200) {
  header('Refresh:2; url=' . $newURL );
  echo "This message is too long";
  exit();
}
if($nlength > 25 ) {
  header('Refresh:2; url=' . $newURL );
  echo "The name is too long";
  exit();
}



$data = json_decode(file_get_contents('test.json'), true);


foreach($data as $post) {
	if ($post["message"] == $message) {
		echo "Another message with this text already exists";
  		header('Refresh:2; url=' . $newURL );
		exit();
	}
}


array_unshift($data , $ndata);
file_put_contents('test.json', json_encode($data, JSON_PRETTY_PRINT));

header('Refresh:2; url=' . $newURL );
echo "Your submisson has been added";
exit();