Page template for WordPress with caching

filters-for-simple-cache-template.php

<?php
add_action( 'save_post', 'clear_many_sites_transient', 10, 1 );
add_action( 'edit_post', 'clear_many_sites_transient', 10, 1 );

function clear_many_sites_transient( $post_id ){

	$post = get_post( $post_id );
	
	if( 'page' === $post->post_type )
		delete_transient( 'many_sites_in_one' );
		
	return $post_id;
	
}

simple-cache-template.php

<?php
/*
Template Name: Many sites in one (with caching)
*/

// set expiration of transient
/*
 * 86400 = 1 day
 * 604800 = 1 week
 * 2592000 = 1 month
 */
$expiration = 86400;

// create filepath for caching file
$upload_dir = wp_upload_dir();
$cache_file = $upload_dir['basedir'] . '/many_sites.cache';
$is_cached = file_exists( $cache_file ) && is_readable( $cache_file );

// get cache transient
if( ( TRUE === get_transient( 'many_sites_in_one' ) ) && $is_cached ){

	exit( file_get_contents( $cache_file ) );
	
} else {
	
	ob_start();
	
	/*
	 * create your site here
	 */
	 
	$content = ob_get_clean();
	 
	$filehandle = fopen( $cache_file, 'w+' );
	 
	if( $filehandle ){
		fwrite( $filehandle, $content );
		fclose( $filehandle );
	}
	
	$is_cached = file_exists( $cache_file ) && is_readable( $cache_file );
	
	set_transient( 'many_sites_in_one', $is_cached, $expiration );
	
	echo $content;
	
}