Prototype for patch https://www.drupal.org/node/2812659

gistfile1.txt

<?php

namespace Drupal\address\Plugin\search_api\processor;

use Drupal\Component\Utility\Html;
use Drupal\Component\Render\FormattableMarkup;
use Drupal\Core\Form\FormStateInterface;
use Drupal\search_api\Processor\FieldsProcessorPluginBase;

/**
 * Makes searches case-insensitive on selected fields.
 *
 * @SearchApiProcessor(
 *   id = "address_abbreviations_to_full_form",
 *   label = @Translation("Address Field : Convert Abbreviations into Full Text Form."),
 *   description = @Translation("Converts abbreviations to its full text form. Components supported are country_code, administrative_area, locality, and dependent_locality"),
 *   stages = {
 *     "pre_index_save" = 0,
 *     "preprocess_index" = -20,
 *     "preprocess_query" = -20
 *   }
 * )
 */
class AddressAbbreviationsToFullForm extends FieldsProcessorPluginBase {

  /**
   * The address format repository.
   *
   * @var \CommerceGuys\Addressing\AddressFormat\AddressFormatRepositoryInterface
   */
  protected $addressFormatRepository;

  /**
   * The subdivision repository.
   *
   * @var \CommerceGuys\Addressing\Country\CountryRepositoryInterface
   */
  protected $countryRepository;

  /**
   * The subdivision repository.
   *
   * @var \CommerceGuys\Addressing\Subdivision\SubdivisionRepositoryInterface
   */
  protected $subdivisionRepository;

  /**
   * The address module field list of compontents supported by this processor.
   *
   */
  protected $supportedComponents;

  /**
   * {@inheritdoc}
   */
  public function __construct(array $configuration, $plugin_id, array $plugin_definition) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->addressFormatRepository = \Drupal::service('address.address_format_repository');
    $this->countryRepository = \Drupal::service('address.country_repository');
    $this->subdivisionRepository = \Drupal::service('address.subdivision_repository');
    $this->supportedComponents = ['country_code', 'administrative_area', 'locality', 'dependent_locality'];
  }

  /**
   * {@inheritdoc}
   */
  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
    $fields = $this->index->getFields();
    $supported_fields = [];
    foreach ($fields as $name => $field) {
      $is_supported = FALSE;
      foreach ($this->supportedComponents as $compontent) {
        if ((strpos($field->getPropertyPath(), ':' . $compontent) !== FALSE)) {
          $is_supported = TRUE;
        }
      }
      if (!$is_supported) {
        continue;
      }
      $supported_field = $field->getPropertyPath();
      $form[$supported_field] = [
        '#type' => 'fieldset',
        '#title' => Html::escape($field->getPrefixedLabel()),
        '#collapsible' => FALSE,
        '#collapsed' => FALSE,
      ];
      $form[$supported_field]['enable'] = [
        '#type' => 'checkbox',
        '#title' => $this->t('Enable'),
        '#default_value' => $this->configuration[$supported_field]['enable'],
      ];
      $form[$supported_field]['concat'] = [
        '#type' => 'checkbox',
        '#title' => $this->t('Concat'),
        '#description' => $this->t('Combine code and full text using a dash separator. eg. {abbreviation} - {full text}'),
        '#default_value' => $this->configuration[$supported_field]['concat'],
      ];
    }
    return $form;
  }

  /**
   * Parses Plugin Configuration Form Values to usable plugin configuration array.
   *
   * @return array
   *   Plugin configuration values.
   */
  private function getPluginConfiguration() {
    $config_form_values = $this->configuration;
    $plugin_configuration = [];
    foreach ($config_form_values as $field_and_component => $configuration) {
      list($field, $component) = explode(':', $field_and_component);
      $plugin_configuration[$field][$component] = $configuration;
    }
    return $plugin_configuration;
  }

  /**
   * Retrieves full text value of an addressfield component.
   *
   * @return string
   *   Full text value of an addressfield component code value.
   */
  private function triangulateCodeToFulltext($field_value, $target, $configuration) {
    $addressFormat = $this->addressFormatRepository->get($field_value['country_code']);
    $current = $result = $field_value[$target];
    $countries = $subdivisions = [];
    switch ($target) {
      case 'country_code':
        $countries = $this->countryRepository->getAll();
        break;
      case 'administrative_area':
        $subdivisions = $this->subdivisionRepository->getAll([$field_value['country_code']]);
        break;
      case 'locality':
        $subdivisions = $this->subdivisionRepository->getAll([$field_value['country_code'], $field_value['administrative_area']]);
        break;
      case 'dependent_locality':
        $subdivisions = $this->subdivisionRepository->getAll([$field_value['country_code'], $field_value['administrative_area'], $field_value['locality']]);
        break;
    }
    if ($target == 'country_code') {
      if (empty($countries[$current])) {
        return $result;
      }
      $code = $countries[$current]->getCountryCode();
      $name = $countries[$current]->getName();
    }
    elseif (in_array($target, ['administrative_area', 'locality', 'dependent_locality'])) {
      if (empty($subdivisions[$current])) {
        return $result;
      }
      $code = $subdivisions[$current]->getCode();
      $name = $subdivisions[$current]->getName();
    }
    if ($configuration['concat'] && ($current != $name)) {
      $result = $code . ' - ' . $name;
    }
    elseif (!$configuration['concat'] && ($current != $name)) {
      $result = $name;
    }
    return $result;
  }

  /**
   * {@inheritdoc}
   */
  public function preprocessIndexItems(array $items) {
    $plugin_configuration = $this->getPluginConfiguration();
    foreach ($items as $item) {
      foreach ($item->getFields() as $name => $field) {
        list($field_name, $component) = explode(":", $field->getPropertyPath());
        if (!isset($plugin_configuration[$field_name]) ||
          !isset($plugin_configuration[$field_name][$component]) ||
          empty($plugin_configuration[$field_name][$component]['enable'])
          ) {
          continue;
        }
        $entity_adapter = $item->getOriginalObject();
        $entity = $entity_adapter->getValue();
        $field_values = $entity->get($field_name)->getValue();
        $new_data = [];
        foreach ($field_values as $delta => $field_value) {
          // override targeted component code value with full text value.
          $new_data[$delta] = $this->triangulateCodeToFulltext($field_value, $component, $plugin_configuration[$field_name][$component]);
        }
        $field->setValues($new_data);
        if ($this->testField($name, $field)) {
          $this->processField($field);
        }
      }
    }
  }

}