Show week numbers in month view

loop-grid.php

<?php
/**
 * Month View Grid Loop
 * This file sets up the structure for the month grid loop
 *
 * Override this template in your own theme by creating a file at [your-theme]/tribe-events/month/loop-grid.php
 *
 * @package TribeEventsCalendar
 * @version 4.6.19
 *
 */

if ( ! defined( 'ABSPATH' ) ) {
	die( '-1' );
} ?>

<?php
$days_of_week = tribe_events_get_days_of_week();
array_unshift( $days_of_week, 'Viikko' );
$week = 0;
global $wp_locale;
function tribe_get_week_num( $date ) {
	$date = new DateTime( $date ) ;
	$week = $date->format("W");
	return $week;
}

?>

<style>
	.week-num {
		text-align: center;
	}
</style>

<?php do_action( 'tribe_events_before_the_grid' ) ?>

	<h2 class="tribe-events-visuallyhidden"><?php printf( esc_html__( 'Calendar of %s', 'the-events-calendar' ), tribe_get_event_label_plural() ); ?></h2>

	<table class="tribe-events-calendar">
		<caption class="tribe-events-visuallyhidden"><?php printf( esc_html__( 'Calendar of %s', 'the-events-calendar' ), tribe_get_event_label_plural() ); ?></caption>
		<thead>
		<tr>
			<?php foreach ( $days_of_week as $day ) : ?>
				<th id="tribe-events-<?php echo esc_attr( strtolower( $day ) ); ?>" title="<?php echo esc_attr( $day ); ?>" data-day-abbr="<?php echo esc_attr( $wp_locale->get_weekday_abbrev( $day ) ); ?>"><?php echo $day ?></th>
			<?php endforeach; ?>
		</tr>
		</thead>
		<tbody>
		<tr>

			<?php $first_in_row = true; ?>
			<?php while ( tribe_events_have_month_days() ) : tribe_events_the_month_day(); ?>
			<?php if ( $week != tribe_events_get_current_week() ) : $week ++; $first_in_row = true; ?>
		</tr>
		<tr>
			<?php endif; ?>

			<?php
			// Get data for this day within the loop.
			$daydata = tribe_events_get_current_month_day(); ?>

			<?php // if this is the first column in the row, add week number ?>
			<?php if ( $first_in_row ) : ?>
			<td class="<?php tribe_events_the_month_day_classes() ?>">
				<?php echo '<p class="week-num" style="text-align: center;">' . tribe_get_week_num( $daydata['date'] ) . '</p>' ; ?>
			</td>
			<?php $first_in_row = false; ?>
			<?php endif; ?>

			<td class="<?php tribe_events_the_month_day_classes() ?>"
				data-day="<?php echo esc_attr( isset( $daydata['daynum'] ) ? $daydata['date'] : '' ); ?>"
				data-tribejson='<?php echo tribe_events_template_data( null, array( 'date_name' => tribe_format_date( $daydata['date'], false ) ) ); ?>'
				>
				<?php tribe_get_template_part( 'month/single', 'day' ) ?>
			</td>

			<?php endwhile; ?>
		</tr>
		</tbody>
	</table><!-- .tribe-events-calendar -->
<?php
do_action( 'tribe_events_after_the_grid' );