Adds a post class that matches the event's status code

event_status_post_class.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

add_filter( 'post_class', 'my_ee_event_status_post_class' );
function my_ee_event_status_post_class( $classes ) {
  global $post;
  if ( 'espresso_events' == get_post_type() ) {
    $event_obj = $post->EE_Event;
    if ( $event_obj instanceof EE_Event ) {
      $classes[] = $event_obj->get_active_status();
    }
  }
  return $classes;
}