public function add( $args, $_ ) {

		$successes = 0;
		$errors    = 0;
		$users     = $this->fetcher->get_many( $args );
		if ( count( $users ) !== count( $args ) ) {
			$errors = count( $args ) - count( $users );
		}
		$user_logins      = wp_list_pluck( $users, 'user_login' );
		$super_admins     = self::get_admins();
		$num_super_admins = count( $super_admins );

		foreach ( $user_logins as $user_login ) {
			if ( in_array( $user_login, $super_admins, true ) ) {
				WP_CLI::warning( "User '{$user_login}' already has super-admin capabilities." );
				continue;
			}

			$super_admins[] = $user_login;
			$successes++;
		}

		if ( count( $super_admins ) === $num_super_admins ) {
			if ( $errors ) {
				$user_count = count( $args );
				WP_CLI::error( "Couldn't grant super-admin capabilities to {$errors} of {$user_count} users." );
			} else {
				WP_CLI::success( 'Super admins remain unchanged.' );
			}
		} else {
			if ( update_site_option( 'site_admins', $super_admins ) ) {
				if ( $errors ) {
					$user_count = count( $args );
					WP_CLI::error( "Only granted super-admin capabilities to {$successes} of {$user_count} users." );
				} else {
					$message = $successes > 1 ? 'users' : 'user';
					WP_CLI::success( "Granted super-admin capabilities to {$successes} {$message}." );
				}
			} else {
				WP_CLI::error( 'Site options update failed.' );
			}
		}
	}