render

$post_type = $attributes['postType'];
$parent_post_id = isset( $attributes['postParent'] ) ? [ $attributes['postParent'] ] : [];

$events_query = new WP_Query(
    [
        'post_type'      => $post_type,
        'posts_per_page' => -1,
        'orderby'        => 'meta_value',
        'post_parent__in' => $parent_post_id,
        'meta_key'       => $post_type . '_date',
        'order'          => 'ASC',
    ]
);

if ( ! $events_query->have_posts() ) {
    return;
}

$events = [];

while ( $events_query->have_posts() ) {
    $events_query->the_post();

    $event_start_date = date( 'Y-m-d', strtotime( get_post_meta( get_the_ID(), $post_type . '_date', true ) ) );
    $event_end_date = date( 'Y-m-d H:i:s', strtotime( get_post_meta( get_the_ID(), $post_type . '_end_date', true ) . ' 23:59:59' ) );

    $recurrence_type = get_post_meta( get_the_ID(), $post_type . '_recurrence', true );
    $recurrence_end_date = get_post_meta( get_the_ID(), $post_type . '_recurrence_end', true );

    $custom_dates = get_post_meta( get_the_ID(), $post_type . '_custom_dates', true );

    $recurrence_end_timestamp = ! empty( $recurrence_end_date ) ? strtotime( $recurrence_end_date . ' 23:59:59' ) : null;
    $last_date_of_recurrance = ! empty( $recurrence_end_date ) ? date( 'Y-m-d', strtotime( $recurrence_end_date ) ) : '';

    switch ( $recurrence_type ) {
        case 'weekly':
            $i = 0;
            do {
                $next_start_date = date( 'Y-m-d', strtotime( $event_start_date . ' + ' . ( 7 * $i ) . ' days' ) );
                $next_end_date = date( 'Y-m-d H:i:s', strtotime( $event_end_date . ' + ' . ( 7 * $i ) . ' days' ) );

                if (
                    strtotime( $next_end_date ) >= strtotime( 'today' ) &&
                    ( ! $recurrence_end_timestamp || strtotime( $next_start_date ) <= $recurrence_end_timestamp )
                ) {
                    $events[] = [
                        'title' => get_the_title(),
                        'url'   => get_the_permalink(),
                        'start' => $next_start_date,
                        'end'   => $next_end_date,
                    ];
                }

                $i++;
            } while (
                ( $recurrence_end_timestamp && strtotime( $next_start_date ) <= $recurrence_end_timestamp ) ||
                ( ! $recurrence_end_timestamp && $i < 10 )
            );
            break;

        case 'monthly':
            $i = 0;
            do {
                $next_start_date = date( 'Y-m-d', strtotime( $event_start_date . ' + ' . $i . ' month' ) );
                $next_end_date = date( 'Y-m-d', strtotime( $event_end_date . ' + ' . $i . ' month' ) );

                if ( strtotime( $next_start_date ) >= strtotime( 'today' ) &&
                     ( ! $recurrence_end_timestamp || strtotime( $next_start_date ) <= $recurrence_end_timestamp ) ) {
                    $events[] = [
                        'title' => get_the_title(),
                        'url'   => get_the_permalink(),
                        'start' => $next_start_date,
                        'end'   => $next_end_date,
                    ];
                }

                $i++;
            } while (
                ( $recurrence_end_timestamp && strtotime( $next_start_date ) <= $recurrence_end_timestamp ) ||
                ( ! $recurrence_end_timestamp && $i < 10 )
            );
            break;

        case 'custom':
            if ( ! empty( $custom_dates ) ) {
                foreach ( $custom_dates as $custom_date ) {
                    $start = isset( $custom_date['start'] ) ? date( 'Y-m-d', strtotime( $custom_date['start'] ) ) : '';
                    $end = isset( $custom_date['end'] ) ? date( 'Y-m-d', strtotime( $custom_date['end'] . ' +1 day' ) ) : '';

                    if ( $start && ( empty( $recurrence_end_timestamp ) || strtotime( $start ) <= $recurrence_end_timestamp ) ) {
                        if ( strtotime( $end ) >= strtotime( 'today' ) ) {
                            $events[] = [
                                'title' => get_the_title(),
                                'url'   => get_the_permalink(),
                                'start' => $start,
                                'end'   => $end,
                            ];
                        }
                    }
                }
            }
            break;

        default:
            if ( strtotime( $event_end_date ) >= strtotime( 'today' ) ) {
                $events[] = [
                    'title' => get_the_title(),
                    'url'   => get_the_permalink(),
                    'start' => $event_start_date,
                    'end'   => $event_end_date,
                ];
            }
            break;
    }
}
wp_reset_postdata();
?>

<div <?php echo wp_kses_data( get_block_wrapper_attributes() ); ?>>
    <div id="event-calendar" data-events="<?php echo esc_attr( json_encode( $events ) ); ?>"></div>
</div>