[CMSP-1140] Fix core resource URLs for non-main sites in subdirectory…

… multisite network (#130)

* add filter to correct the path for core resources
for non-main sites on subdirectory multisites

* lower priority
so it's easier to override

* loop through filter hooks rather than explicitly adding individually

Co-authored-by: Phil Tyler <[email protected]>

* remove if/else chain and replace with an array to loop through

Co-authored-by: Phil Tyler <[email protected]>

---------

Co-authored-by: Phil Tyler <[email protected]>

web/app/mu-plugins/filters.php

@@ -28,3 +28,65 @@
 add_filter( 'pantheon.multisite.config_filename', function ( $config_filename ) {
     return 'config/application.php';
 } );
+
+/**
+ * Correct core resource URLs for non-main sites in a subdirectory multisite network.
+ *
+ * @param string $url The URL to fix.
+ * @return string The fixed URL.
+ */
+function fix_core_resource_urls( $url ) {
+    $main_site_url = trailingslashit( network_site_url( '/' ) );
+    $current_site_path = trailingslashit( get_blog_details()->path );
+
+    // Parse the URL to get its components.
+    $parsed_url = parse_url( $url );
+
+    // If there is no path in the URL, return it as is.
+    if ( ! isset( $parsed_url['path'] ) || $parsed_url['path'] === '/' ) {
+        return $url;
+    }
+
+$core_paths = [ 'wp-includes/', 'wp-admin/', 'wp-content/' ];
+$path_modified = false;
+
+foreach ( $core_paths as $core_path ) {
+    if ( strpos( $path, $current_site_path . $core_path ) !== false ) {
+        $path = str_replace( $current_site_path . $core_path, $core_path, $path );
+        $path_modified = true;
+        break;
+    }
+}
+
+// If the path was not modified, return the original URL.
+if ( ! $path_modified ) {
+    return $url;
+}
+
+    // Prepend the main site URL to the modified path.
+    $new_url = $main_site_url . ltrim( $path, '/' );
+
+    // Append any query strings if they existed in the original URL.
+    if ( isset( $parsed_url['query'] ) ) {
+        $new_url .= '?' . $parsed_url['query'];
+    }
+
+    return $new_url;
+}
+
+// Only run the filter on non-main sites in a subdirectory multisite network.
+if ( is_multisite() && ! is_subdomain_install() && ! is_main_site() ) {
+$filters = [
+    'script_loader_src',
+    'style_loader_src',
+    'plugins_url',
+    'theme_file_uri',
+    'stylesheet_directory_uri',
+    'template_directory_uri',
+    'site_url',
+    'content_url'
+];
+foreach ( $filters as $filter ) {
+    add_filter( $filter, 'fix_core_resource_urls', 9 );
+}
+}