PHP: Запись в файл по клику на checkbox

<?php
if(isset($_POST['inputtags']))
{
 $f=fopen($_SERVER['DOCUMENT_ROOT']."/engine/inputtags.txt","w");
 fwrite($f,"1");
 fclose($f);
}
else
{
$f=fopen($_SERVER['DOCUMENT_ROOT']."/engine/inputtags.txt","w");
 fwrite($f,"0");
 fclose($f);
}

$check_tags=file($_SERVER['DOCUMENT_ROOT']."/engine/inputtags.txt");
if($check_tags[0]==1)$check_tags="checked";
else $check_tags="";
?>

<form action method="post" name="rectags">
<input type="checkbox" id="humantags" name="inputtags" onclick="rectags.submit();" <?php echo $check_tags?>>
<label for="humantags">1 или 0</label>
</form>