Add capacity control to services of WPMUDEV Appointments+ plugin

app-capacity-control.php

<?php
/*
Plugin Name: Appointments capacity control
Plugin URI: https://premium.wpmudev.org/
Description: Add capacity control to services
Author: Panos Lyrakis @ WPMUDEV
Author URI: https://premium.wpmudev.org/
License: GPLv2 or later
*/


/*
Requires to modify function apppointments_is_range_busy()
and add the following somwhere on the beginning :

=============

$force_availability = apply_filters( 'app-force_availability', false, $start, $end, $args );
if( $force_availability ){
$is_busy = apply_filters( 'app-is_busy_custom', false, $start, $end, $args );
return $is_busy;
}

============

*/

     if( ! class_exists( 'WPMUDEV_App_Capacity_Control' ) ){
     class WPMUDEV_App_Capacity_Control{
          private static $_instance = null;
          public $version;
          public static function get_instance() {
               if ( is_null( self::$_instance ) ) {
                    self::$_instance = new WPMUDEV_App_Capacity_Control();
               }
               return self::$_instance;
          }

          private function __construct(){

               add_filter( 'app-force_availability', array( $this, 'force_availability' ), 10, 4 );
               add_filter( 'app-is_busy_custom', array( $this, 'is_busy' ), 10, 4 );
               add_filter( 'app_additional_fields', array( $this, 'additional_field'), 10  );
               add_action( 'wpmudev_appointments_insert_appointment', array( $this, 'save_additional_fields' ), 10 );

               add_action( 'wp_ajax_pre_confirmation_slot_capacity', array( $this, 'ajax_slot_capacity' ) );
               add_action( 'wp_ajax_nopriv_pre_confirmation_slot_capacity', array( $this, 'ajax_slot_capacity' ) );

               /*
               //TODO
               add_filter('app_notification_message', array($this, 'expand_email_macros'), 10, 3);
     		add_filter('app_confirmation_message', array($this, 'expand_email_macros'), 10, 3);
     		add_filter('app_reminder_message', array($this, 'expand_email_macros'), 10, 3);
     		add_filter('app_removal_notification_message', array($this, 'expand_email_macros'), 10, 3);
               */

          }

          public function force_availability( $force_it, $start, $end, $args ){
               return true;
          }


          public function is_busy( $is_busy, $start, $end, $args ){

               $service_id 			     = (int)$args['service_id'];
               $start 					= date( 'Y-m-d H:i:s', $start );
               $end 					= date( 'Y-m-d H:i:s', $end );

               $av_args = array(
                    'service_id'   => $service_id,
                    'start'        => $start,
                    'end'          => $end
               );

               $service_capacity = $this->get_availability( $av_args );
               return ! $service_capacity > 0;

          }

          public function get_availability( $args ){

               global $wpdb;

               $service_id 			     = (int)$args['service_id'];
               $service                      = appointments_get_service( $service_id );
               $service_capacity 		     = (int)$service->capacity; //appointments_get_service_capacity( $service_id ); //(int)$args[ 'capacity' ];
/*
               $service_id 			     = (int)$args['service_id'];
               $start 					= (int)$args['start'];
               $end 					= (int)$args['end'];

               $un_args = array(
                    'service_id'   => $service_id,
                    'start'        => $start,
                    'end'          => $end
               );
               */
               $unavail = self::get_unavail( $args );

               if( is_numeric( $unavail ) && $unavail > 0 ){

                    $workers_count			= count( appointments_get_workers_by_service( $service_id ) );
                    $service_capacity 		= $workers_count * $service_capacity;
                    $service_capacity        -= $unavail;

                    //return ! $service_capacity > 0;
               }

               //return false;
               return $service_capacity;

          }


          public static function get_unavail( $args ){

               global $wpdb;

               $service_id 			     = $args[ 'service_id' ];
               $start 					= $args[ 'start' ];
               $end 					= $args[ 'end' ];

               $booked_query = "SELECT SUM( app_meta.meta_value ) AS unavail FROM {$wpdb->prefix}app_appointments as app
               LEFT JOIN {$wpdb->prefix}app_appointmentmeta AS app_meta ON app.ID = app_meta.app_appointment_id
               WHERE
               app.service={$service_id} AND app.status IN( 'pending','confirmed', 'paid' ) AND ( ( app.start BETWEEN '{$start}' AND '{$end}' ) OR ( app.end BETWEEN '{$start}' AND '{$end}' ) ) AND app_meta.meta_key = 'app_item_count'";

               return $wpdb->get_var( $booked_query );

          }

          public function ajax_slot_capacity(){

               $service_id              = (int)$_POST[ 'service_id' ];
               $start                   = date('Y-m-d H:i:s', $_POST[ 'start' ] );
               $end                     = date('Y-m-d H:i:s', $_POST[ 'end' ] );

               $args = array(
                    'service_id'   => $service_id,
                    'start'        => $start,
                    'end'          => $end
               );

               $availability = $this->get_availability( $args );
               $response = array( 'capacity' => $availability );

               wp_send_json( $response );

          }

          public function additional_field( $fields_html ){

               global $wpdb;

               //$services_capacities = $wpdb->get_results( "SELECT ID, capacity FROM {$wpdb->prefix}app_services", ARRAY_A );

               ob_start();
               ?>
               <div class="appointments-capacity-field">
				<label>
					<span>Select number</span>
                         <select name="app-service-capacity-select" id="app-service-capacity-select"></select>
				</label>
			</div>

               <script type="text/javascript">

                    (function($){
                         $(document).ready(function(){

                              $.ajaxSetup({
                         		beforeSend: function (jqxhr, settings) {
                         				settings.data += '&' + encodeURIComponent( 'app-service-capacity-select' ) + '=' + encodeURIComponent( $( '#app-service-capacity-select' ).val() );
                         		}
                         	});

                              //var services_capacities = JSON.parse( '<?php //echo json_encode( $services_capacities ); ?>' );

                              var $body = $('body');
                              var capacity_selector = $( '#app-service-capacity-select' );
                              $body.on( 'click', '.app_timetable_cell.free, .app_week_timetable_cell.free', function( $element ) {

                                   /*if( ! isNaN( selected_service ) ){
                                        return;
                                   }*/
                                   var confirmation_btn     = $( '.appointments-confirmation-button' );
                                   var selected_slot_meta   = $( this ).find( '.appointments_take_appointment' ).val();
                                   var selected_meta_parts  = selected_slot_meta.split(':');
                                   var selected_service     = selected_meta_parts[1];
                                   var start                = selected_meta_parts[3];
                                   var end                  = selected_meta_parts[4];

                                   var cap_data = {
                                        action              : "pre_confirmation_slot_capacity",
                                        nonce               : AppShortcodeConfirmation.nonce,
                                        service_id          : selected_service,
                                        start               : start,
                                        end                 : end
                                   };

                                   confirmation_btn.hide( 300 );

                                   $.post( AppShortcodeConfirmation.ajaxurl, cap_data, function( response ) {

                                        var capacity = 1;

                                        if ( response && response.error ) {
                                             //Just do nothing and leave capacity to 1
                                             //console.log( 'No capacity response' );
                                        }
                                        else{
                                             capacity = response.capacity;
                                        }

                                        var selector_options = '';
                                        for( var c = 1; c <= capacity; c++ ){
                                             selector_options += '<option value="' + c + '">' + c + '</option>';
                                        }

                                        capacity_selector.append( selector_options );

                                        confirmation_btn.show( 300 );

                                   }, 'json');

                                   /*$.each(services_capacities, function(i,item){
                                        if( item.ID == selected_service ){
                                             capacity = item.capacity;
                                        }
                                   });*/

                              } );

                         });
                    })(jQuery);

               </script>
               <?php
               $capacity_selector = ob_get_clean();

               return $fields_html . $capacity_selector;

          }

          public function save_additional_fields( $app_id ){

               if( ! isset( $_REQUEST[ 'app-service-capacity-select' ] ) || ! is_numeric( $_REQUEST[ 'app-service-capacity-select' ] ) ){
                    return;
               }

               $capacity_selected = (int)$_REQUEST['app-service-capacity-select'];

               update_metadata( 'app_appointment', $app_id, 'app_item_count', $capacity_selected );

          }

     }

     add_action( 'plugins_loaded', function(){
          $GLOBALS['WPMUDEV_App_Capacity_Control'] = WPMUDEV_App_Capacity_Control::get_instance();
     }, 10 );

}

In order the above to work on Appointments+ version 2.1.0 you need to modify file
includes/helpers.php
and add the following at the beginning of function apppointments_is_range_busy():

$force_availability = apply_filters( 'app-force_availability', false, $start, $end, $args ); if( $force_availability ){ $is_busy = apply_filters( 'app-is_busy_custom', false, $start, $end, $args ); return $is_busy; }