Wordpress Buffer HTML Cache - php

Question

I'm writing a plugin that writes the HTML output to the file and loads the site from that file, next time. It works flawlessly. But I can't cache the code after the wp_footer hook. I tried the "shutdown" hook that works after the wp_footer hook but it returns null. I don't know why it is returning null. But I need a hook that runs after the wp_footer hook, where I can cache all the code from 0 to 100.
<?php
$priority = 10;
add_action('template_redirect', function(){
if(!is_admin() && !is_user_logged_in()){
$cache_time = get_option('html_cache_time');
if(empty($cache_time)){
$cache_time = 60;
}
$current_url = get_site_url() . $_SERVER['REQUEST_URI'];
if(filter_var($current_url, FILTER_SANITIZE_URL)){
$parsed_url = parse_url($current_url);
$url_path = isset($parsed_url['path']) ? $parsed_url['path'] : false;
if(!empty($url_path)){
$cached_url = NGY_CACHE_DIR . 'app/cached/' . md5($url_path) . '.cache';
define('NOGAY_CACHED_URL', $cached_url);
$end_time = 60 * $cache_time;
if(file_exists($cached_url)){
if(time() - $end_time < filemtime($cached_url)){
readfile($cached_url);
exit;
}else{
unlink($cached_url);
}
}
}
}
ob_start();
}
}, $priority);
add_action('wp_footer', function(){
if(!is_admin() && !is_user_logged_in()){
$html = ob_get_clean();
if(!file_exists(NOGAY_CACHED_URL)){
echo $html;
}
$open_cached_file = fopen(NOGAY_CACHED_URL, 'w+');
fwrite($open_cached_file, $html);
fclose($open_cached_file);
ob_end_flush();
}
}, PHP_INT_MAX);
I tried another Wordpress hooks. (shutdown)