Function to Determine if Multisite is Active and Enabled

ms-detection.php

/**
 * Checks if the plugin is on a multisite install and if plugin is active for network.
 *
 * @param bool $network_admin Whether to check if in the network admin.
 * @param bool $network_activated Whether the plugin is active for the network.
 * @param mixed $plugin_file Path to the plugin file.
 *
 * @return bool True if multisite, false if not. If in network admin, true if plugin is active for network, false if not. If not in network admin, true if plugin is active for the site, false if not.
 */
function dlx_is_multisite( $network_admin = false, $network_activated = false, $plugin_file = __FILE__ ) {
	if ( ! function_exists( 'is_plugin_active_for_network' ) ) {
		require_once ABSPATH . '/wp-admin/includes/plugin.php';
	}
	if ( $network_admin ) {
		if ( is_network_admin() ) {
			if ( is_multisite() ) {
				if ( $network_activated ) {
					if ( is_plugin_active_for_network( plugin_basename( $plugin_file ) ) ) {
						return true;
					}
				} else {
					return true;
				}
			}
		} else {
			return false;
		}
	}
	if ( is_multisite() ) {
		if ( $network_activated ) {
			if ( is_plugin_active_for_network( plugin_basename( $plugin_file ) ) ) {
				return true;
			}
		} else {
			return true;
		}
	}
	return false;
}