body-class-event.php

/**
 * A function which adds classes to event pages corresponding to the event
 * E.g. adds 'eo-event-cat-[cat slug]' class for each category the event belongs to.
 * Adds 'eo-event-venue-[venue slug]' if the event has a venue
 * Adds time based class: eo-event-future/past/running for future/past/running events
 *
 * @url http://wordpress.org/support/topic/problem-with-highlight-in-menu-change-url-of-events?replies=8#post-3458829
 * Not tested
*/
add_filter( 'body_class', 'my_event_organiser_add_classes_to_event_body');
function my_event_organiser_add_classes_to_event_body($classes){

     if( !is_singular('event') )
          return $classes;

     //Add category classes
     $cats= get_the_terms(get_the_ID(), 'event-category');
     if( $cats ){	
          foreach ($cats as $cat)
               $classes[] = esc_attr('eo-event-cat-'.$cat->slug);
     }

     //Add venue class
     if( eo_get_venue_slug() )
          $classes[] = esc_attr('eo-event-venue-'.eo_get_venue_slug());

     $start = eo_get_the_start(DATETIMEOBJ);
     $end= eo_get_the_end(DATETIMEOBJ);
     $now = new DateTime('now',eo_get_blog_timezone());

     //Add 'time' class
     if( $start > $now ){
        $classes[] = 'eo-event-future';
     }elseif( $end < $now ){
        $classes[] = 'eo-event-past';
     }else{
        $classes[] = 'eo-event-running';
     }
     return $classes;
}