Specify default appointment service from shortcode

appointments_default_service.php

<?php

/**
* Plugin Name: Specify Default Appointment Service
* Plugin URI: https://premium.wpmudev.org/
* Description: Specify default appointment service from shortcode
* Author: Ariful Islam @ WPMUDEV
* Author URI: https://premium.wpmudev.org/profile/itsarifulislam
* License: GPLv2 or later
*/

/*
*
* Example of use: [app_services default="2"]
*
*/


if ( ! defined( 'ABSPATH' ) ) {
	exit;
}


if ( ! class_exists( 'Appointment_Default_Service' ) ) {

	class Appointment_Default_Service {

		private static $_instance = null;

		public static function get_instance() {

			if( is_null( self::$_instance ) ) {
				self::$_instance = new Appointment_Default_Service();
			}

			return self::$_instance;

		}


		private function __construct() {

			add_filter('appointments_services_shortcode_selected_service', array( $this, 'appointments_services_shortcode_selected_service' ), 10, 2);
			
		}


		public function appointments_services_shortcode_selected_service( $selected_service, $args ) {

			if ( isset( $args['default'] ) ) {
				$selected_service = $args['default'];
			}

			return $selected_service;

		}

	}


	function render_appointment_default_service(){

		$GLOBALS['Appointment_Default_Service'] = Appointment_Default_Service::get_instance();

	}

	add_action( 'plugins_loaded', 'render_appointment_default_service' );

}

Example of use: [app_services default="2"]