function start_next_ical_update() {
  //fetch ical scheduled imports and get the ones that have not been manually imported for at least a day
  $args = array(
    'post_type' => 'tribe-ea-record',
    'post_status' => 'tribe-ea-schedule',
    'ping_status' => 'schedule',
    'post_mime_type' => 'ea/ical',
    'posts_per_page' => -1,
    'meta_query' => array(
        'relation' => 'OR',
        array(
            'key' => '_tribe_ics_hack',
            'value' => time()-86400,
            'compare' => ' '_tribe_ics_hack',
           'compare' => 'NOT EXISTS'
        )  ),
    'orderby' => '_tribe_ics_hack',
    'order' => 'ASC');
  $query = new WP_Query( $args );

  //start the update for the one that has not been updated the longest
  if($query->have_posts()) {
    $item = $query->posts[0];
    $meta = get_post_meta($item->ID);
    $url = $meta['_tribe_aggregator_source'][0];
    error_log('started '.$url);
    update_ical_events($url);
    update_post_meta( $item->ID, '_tribe_ics_hack', time());
  }
}

//use the tribe cron every 15 minutes to start the update function
add_action('tribe_aggregator_cron', 'start_next_ical_update', 10, 0);

//during debugging use the json api to start the update manually
//use curl http://your-domain.com/wp-json/pd/v1/updateevents
/*add_action( 'rest_api_init', function () {
  register_rest_route( 'pd/v1', '/updateevents', array(
    'methods' => 'GET',
    'callback' => 'start_next_ical_update',
  ) );
} );*/

function update_ical_events($url) {
  //get ics contents from url
  ini_set('user_agent','Mozilla/4.0 (compatible; MSIE 6.0)');

  try {
    $ics = get_file_contents($url);

    if ($ics === false) {
      return new WP_Error( 'import_error', 'File was empty.');
    }
  } catch (Exception $e) {
    return new WP_Error( 'import_error', 'URL could not be reached.');
  }

  //get wp upload dir and a filename for our ics
  $upload_dir = wp_upload_dir();
  /*preg_match('/[A-Za-z0-9]+\.?[A-Za-z0-9]*$/', $url, $name); */
  $basename = wp_unique_filename($upload_dir['path'], 'manual.ics');

  $file_abs = $upload_dir['path'].'/'.$basename;
  $file_url = $upload_dir['url'] . '/' . $basename;

  //save the ics content to a local file
  $f = fopen($file_abs, "w") or die("Unable to open file!");
  if ( !$f ) {
    return new WP_Error( 'import_error', 'File could not be written.');
  }
  fwrite($f, $ics);
  fclose($f);

  //set permissions
  $stat = stat( dirname( $file_abs ));
  $perms = $stat['mode'] & 0000666;
  chmod( $file_abs, $perms );

  //and add attachement metadata to the file to get it into wp media
  $type = wp_check_filetype( basename( $basename ), null );
  $attachment = array(
    'guid'           => $file_url,
    'post_mime_type' => $type['type'],
    'post_title'     => preg_replace( '/\.[^.]+$/', '', $basename ),
    'post_content'   => '',
    'post_status'    => 'inherit',
    'post_author'    => 1
  );
  $id = wp_insert_attachment( $attachment, $file_abs);
  require_once( ABSPATH . 'wp-admin/includes/image.php' );

  // Generate the metadata for the attachment, and update the database record.
  $attach_data = wp_generate_attachment_metadata( $id, $file_url );
  wp_update_attachment_metadata( $id, $attach_data );

  //prepare settings for event aggregator
  $meta = Array(
    'origin' => 'ics',
    'file' => $id,
    'type' => 'manual',
    'limit_type' => 'no_limit'
  );
  $args = array_merge($meta, Array(
    'allow_multiple_organizers' => true,
    'preview' => true
  ));

  //create new events aggregator import and get the data from the aggregator service
  $import = new Tribe__Events__Aggregator__API__Import();
  $response = $import->create($args);
  $response_data = $response->data;
  $meta['import_id'] = $response_data->import_id;

  //create and save new aggregator record
  $record = Tribe__Events__Aggregator__Records::instance()->get_by_origin( $meta['origin'] );
  $post = $record->create($meta['type'], $args, $meta);

  $record->set_status_as_pending();
  $record->update_meta( 'category', null);
  $record->update_meta( 'post_status', 'publish' );
    $record->finalize();

  //seems to be necessary for larger ics files, gets down failure rate
  sleep(5);

  //process the events and add them
  $result = $record->process_posts();
  $result->record = $record;

  return new WP_REST_Response( $result );
}

function get_file_contents($url, $post = null) {
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
    curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
    curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 0);
    if(!empty($post)) {
        curl_setopt($ch, CURLOPT_POST, true);
        curl_setopt($ch, CURLOPT_POSTFIELDS, $post);
    }
    $result = curl_exec($ch);
    curl_close($ch);
    return $result;
}