ci_views_query_date.module

<?php

/**
 * @file
 *  
 * @author Mike Chaplin, Circle Interactive
 *
 * To change the date in views query to allow chart grouping by year & month. 
 */
 
 use Drupal\views\ViewExecutable;
 use Drupal\views\Plugin\views\query\QueryPluginBase;
 use Drupal\Core\Database\Query\AlterableInterface;
 use Drupal\views\Plugin\views\cache\CachePluginBase;

/**
 *
 * Removing the group_by here allows the sort criteria to take over the grouping (take a look at the SQL in the view edit). 
 */ 
function ci_views_query_date_query_alter(Drupal\Core\Database\Query\AlterableInterface $query) {

  $targetViews = ['data_over_time_chart_updated', 'data_over_time_chart_month', 'data_over_time_chart_quarterly'];

  if ($query->getMetaData('view') && in_array($query->getMetaData('view')->id(),$targetViews) ) {
    
    $user = \Drupal::currentUser();
    if ($user->id()==1):
      $messenger = \Drupal::messenger(); 
      $messenger->addStatus(t('Admin only message: This view is being altered by custom code'));
    endif;     
    
    $group_by =& $query->getGroupBy();
    unset($group_by['node__field_activity_date_field_activity_date_value']);
  }
}

/**
 *
 * This harvests the quarterly months for a new result set, and sets a culmulative value. 
 */
function ci_views_query_date_views_post_render(ViewExecutable $view, array &$output, CachePluginBase $cache) {
  if ($view->id() == 'data_over_time_chart_quarterly'):
    
    $newResults = [];
    $tally = 0;
    $quarterMonths = ["03", "06", "09","12"];
        
    foreach ($view->result as $key => $object):
      $month = substr($object->node__field_activity_date_field_activity_date_value_month, -2);

      if (in_array($month, $quarterMonths)):
        $object->nid = intval($object->nid) + $tally;
        $tally = 0;
        $newResults[] = $view->result[$key];
      else:
        $tally = intval($object->nid) + $tally;
      endif; 

    endforeach;

    $view->result = $newResults;
   endif;
}