Attach an iCal 'invite' to booking confirmation. Please note this snippet is for when you are selling tickets by **series** or you only have non-recurring events.

attach-ical-to-booking-confirmation.php

<?php

/**
 * Please note this snippet is for when you are selling tickets by **series** or you only have non-recurring events.
 * This is because the attached iCal file will detail all dates of the event booked for. 
 * 
 * If you are selling tickets by date, then you should change the get_ical() method so that it returns an iCal feed, which details
 * only the event (date) that has been booked
 *
 * 
 * ### Instructions ###
 * This snippet should go in a dedicated plug-in.
 * Alternatively, it will work in your theme's functions.php. 
 */

class Myprefix_iCal_Email_Attacher{
	
	protected $booking_id = false;
	
	function __construct(){
		add_filter( 'eventorganiser_booking_confirmed_email_attachments', array( $this, 'setup' ), 10, 2 );
	}
	
	function setup( $attachments, $booking_id ){
		$this->booking_id = $booking_id;
		add_action( 'phpmailer_init', array( $this, 'attach_ical' ), 10 );
		add_action( 'phpmailer_init', array( $this, 'cleanup' ), 11 );
		return $attachments;
	}
	
	function attach_ical( $phpmailer ){
		
		if( $this->booking_id ){
					
			$event_id    = eo_get_booking_meta( $this->booking_id , 'event_id' );
			$title       = esc_attr( get_the_title( $event_id ) );			
			$filename    = sanitize_file_name( $title.'-'.$this->booking_id.'.ics' );
			$ical_string = $this->get_ical( $event_id ); 
		
			$phpmailer->AddStringAttachment( $ical_string, $filename );
			
			$this->booking_id = false;
			
		}
		
	}
	
	function get_ical( $event_id ){
		
		//Generate ical string for this event.
		query_posts( array( 'post_type' => 'event', 'p' => $event_id, 'group_events_by' => 'series' ) );	
		ob_start();
		eo_locate_template( 'ical.php', true );;
		$string = ob_get_contents();	
		ob_end_clean();
		wp_reset_query();
		
		return $string;
		
	}
	
	function cleanup(){
		remove_action( 'phpmailer_init', array( $this, 'attach_ical' ), 10 );
	}
	
}
$ical_attacher = new Myprefix_iCal_Email_Attacher();