Adds "Today -" or "Tomorrow -" to the group by day header for Event Calendar Newsletter

ecn-group-by-day-prefix.php

<?php
/*
Plugin Name: Event Calendar Newsletter Pro Today/Tomorrow Prefix
Plugin URI: https://eventcalendarnewsletter.com
Description: Add today/tomorrow prefix to "group by day" header
Version: 1.0
Author: Brian Hogg
Author URI: https://brianhogg.com
Text Domain: event-calendar-newsletter-pro
License: GPL2
*/

/**
 * Add Tonight or Tomorrow depending on the date
 * @param $prefix string
 * @param $event ECNCalendarEvent
 * @param $args array
 * 
 * @return string
 */
function ecn_pro_add_group_by_day_prefix( $prefix, $event, $args ) {
	$today = new DateTime();
	$today->setTime( 0, 0, 0 );

	$match_date = new DateTime();
	$match_date->setTimestamp( $event->get_start_date() );
	$match_date->setTime( 0, 0, 0 ); // reset time part, to prevent partial comparison

	$diff = $today->diff( $match_date );
	$diff_in_days = (integer)$diff->format( "%R%a" ); // Extract days count in interval

	switch ( $diff_in_days ) {
		case 0:
			$prefix .= 'Today - ';
			break;
		case 1:
			$prefix .= 'Tomorrow - ';
			break;
	}
	return $prefix;
}
add_filter( 'ecn_pro_group_by_day_prefix', 'ecn_pro_add_group_by_day_prefix', 10, 3 );