Surge Modifier Proof of Concept

surge-modifier.php

<?php
/*
 * Plugin Name:       Surge Modifier
 * Description:       Modifies the behavior of the Surge caching plugin to aggressively invalidate a subsite's cache when content has changed
 * Version:           3
 * Author:            Jason LeMahieu
 * License:           GPL v2 or later
 * License URI:       https://www.gnu.org/licenses/gpl-2.0.html
 */

/* CHANGELOG
    3: Add save_post

*/

// NOTE: This gist is pending Surge developer feedback. Do not use yet (unless you know what you're doing more than I do)


 /* Flag each entry with the current network and blog id. This should invalidate an entire subsite's cache on any of the impacted actions
    Note: The actual expiring is done by this bit in Surge/includes/invalidate.php, by expiring everything with this same flag
    
    $expire_flag = is_multisite()
		? sprintf( 'network:%d:%d', get_current_network_id(), get_current_blog_id() )
		: '/';

	foreach ( $flush_actions as $action ) {
		if ( did_action( $action ) ) {
			expire( $expire_flag );
			break;
		}
	}
 */
 add_action( 'template_redirect', 'surge_modifier_template_redirect' );

function surge_modifier_template_redirect( ) {
    Surge\flag( sprintf( 'network:%d:%d', get_current_network_id(), get_current_blog_id() ) );
}




/* Invalidate an entire subsite's cache on additional actions */

add_filter( 'surge_flush_actions', 'ext_surge_modifier_filter_surge_flush_actions' );

function ext_surge_modifier_filter_surge_flush_actions( $actions ) {

    $actions[] = 'wp_update_nav_menu';
    $actions[] = 'wp_update_nav_menu_item';
    $actions[] = 'wp_add_nav_menu_item';
    $actions[] = 'delete_widget';
    $actions[] = 'save_post';

    return $actions;
}


/* This example was provided by the plugin author (https://github.com/kovshenin/surge/issues/29)

 // Flag each entry with the current blog id.
add_action( 'template_redirect', function() {
    Surge\flag( sprintf( 'blogid:%d', get_current_blog_id() ) );
} );

// Expire all subsite cache on certain events.
add_action( 'certain_event', function() {
    Surge\expire( sprintf( 'blogid:%d', get_current_blog_id() ) );
} );

*/