<?php
/**
 * Implements hook_search_api_alter_callback_info()
 * Add our own callback for Search API
 */
function search_api_combined_search_api_alter_callback_info() {
  $callbacks['search_api_alter_add_combined'] = array(
    'name' => t('Combined fields'),
    'description' => t('Gives you the ability to define additional fields, combining data from one or more other fields.'),
    'class' => 'SearchApiAlterAddCombined',
  );

  return $callbacks;
}

/**
 * Implements hook_facetapi_facet_info_alter to chance the field and type of the combined facets to
 * match the selected imitation
 * 
 * @param array $facet_info
 * @param array $searcher_info
 */
function search_api_combined_facetapi_facet_info_alter(array &$facet_info, array $searcher_info) {
  $processor_info = search_api_get_processors();
  $index = search_api_index_load($searcher_info['instance']);
  $options = empty($index->options) ? array() : $index->options;
  $callbacks = empty($options['data_alter_callbacks']) ? array() : $options['data_alter_callbacks'];
  $fields = $index->getFields(FALSE);
  
  if (TRUE === isset($callbacks['search_api_alter_add_combined']['settings']['fields']) && 1 == $callbacks['search_api_alter_add_combined']['status']) {
    foreach ($callbacks['search_api_alter_add_combined']['settings']['fields'] as $key => $combined) {
      if (FALSE === empty($combined['imitate']) && TRUE === isset($facet_info[$combined['imitate']])) {
        $facet_info[$key]['field type'] = $facet_info[$combined['imitate']]['field type'];
        $facet_info[$key]['map options']['field'] = array_merge($facet_info[$key]['map options']['field'], $facet_info[$combined['imitate']]['map options']['field']);
      }
    }
  }
}