class ConfigImporterFieldPurger

class ConfigImporterFieldPurger {
    
    /**
     * Processes fields targeted for purge as part of a configuration sync.
     *
     * This takes care of deleting the field if necessary, and purging the data on
     * the fly.
     *
     * @param array $context
     *   The batch context.
     * @param \Drupal\Core\Config\ConfigImporter $config_importer
     *   The config importer.
     */
    public static function process(array &$context, ConfigImporter $config_importer) {
        if (!isset($context['sandbox']['field'])) {
            static::initializeSandbox($context, $config_importer);
        }
        // Get the list of field storages to purge.
        $field_storages = static::getFieldStoragesToPurge($context['sandbox']['field']['extensions'], $config_importer->getUnprocessedConfiguration('delete'));
        // Get the first field storage to process.
        $field_storage = reset($field_storages);
        if (!isset($context['sandbox']['field']['current_storage_id']) || $context['sandbox']['field']['current_storage_id'] != $field_storage->id()) {
            $context['sandbox']['field']['current_storage_id'] = $field_storage->id();
            // If the storage has not been deleted yet we need to do that. This is the
            // case when the storage deletion is staged.
            if (!$field_storage->isDeleted()) {
                $field_storage->delete();
            }
        }
        field_purge_batch($context['sandbox']['field']['purge_batch_size'], $field_storage->getUniqueStorageIdentifier());
        $context['sandbox']['field']['current_progress']++;
        $fields_to_delete_count = count(static::getFieldStoragesToPurge($context['sandbox']['field']['extensions'], $config_importer->getUnprocessedConfiguration('delete')));
        if ($fields_to_delete_count == 0) {
            $context['finished'] = 1;
        }
        else {
            $context['finished'] = $context['sandbox']['field']['current_progress'] / $context['sandbox']['field']['steps_to_delete'];
            $context['message'] = \Drupal::translation()->translate('Purging field @field_label', [
                '@field_label' => $field_storage->label(),
            ]);
        }
    }
    
    /**
     * Initializes the batch context sandbox for processing field deletions.
     *
     * This calculates the number of steps necessary to purge all the field data
     * and saves data for later use.
     *
     * @param array $context
     *   The batch context.
     * @param \Drupal\Core\Config\ConfigImporter $config_importer
     *   The config importer.
     */
    protected static function initializeSandbox(array &$context, ConfigImporter $config_importer) {
        $context['sandbox']['field']['purge_batch_size'] = \Drupal::config('field.settings')->get('purge_batch_size');
        // Save the future list of installed extensions to limit the amount of times
        // the configuration is read from disk.
        $context['sandbox']['field']['extensions'] = $config_importer->getStorageComparer()
            ->getSourceStorage()
            ->read('core.extension');
        $context['sandbox']['field']['steps_to_delete'] = 0;
        $fields = static::getFieldStoragesToPurge($context['sandbox']['field']['extensions'], $config_importer->getUnprocessedConfiguration('delete'));
        foreach ($fields as $field) {
            $row_count = \Drupal::entityTypeManager()->getStorage($field->getTargetEntityTypeId())
                ->countFieldData($field);
            if ($row_count > 0) {
                // The number of steps to delete each field is determined by the
                // purge_batch_size setting. For example if the field has 9 rows and the
                // batch size is 10 then this will add 1 step to $number_of_steps.
                $how_many_steps = ceil($row_count / $context['sandbox']['field']['purge_batch_size']);
                $context['sandbox']['field']['steps_to_delete'] += $how_many_steps;
            }
        }
        // Each field possibly needs one last field_purge_batch() call to remove the
        // last field and the field storage itself.
        $context['sandbox']['field']['steps_to_delete'] += count($fields);
        $context['sandbox']['field']['current_progress'] = 0;
    }
    
    /**
     * Gets the list of fields to purge before configuration synchronization.
     *
     * If, during a configuration synchronization, a field is being deleted and
     * the module that provides the field type is being uninstalled then the field
     * data must be purged before the module is uninstalled. Also, if deleted
     * fields exist whose field types are provided by modules that are being
     * uninstalled their data need to be purged too.
     *
     * @param array $extensions
     *   The list of extensions that will be enabled after the configuration
     *   synchronization has finished.
     * @param array $deletes
     *   The configuration that will be deleted by the configuration
     *   synchronization.
     *
     * @return \Drupal\field\Entity\FieldStorageConfig[]
     *   An array of field storages that need purging before configuration can be
     *   synchronized.
     */
    public static function getFieldStoragesToPurge(array $extensions, array $deletes) {
        $providers = array_keys($extensions['module']);
        $providers[] = 'core';
        $storages_to_delete = [];
        // Gather fields that will be deleted during configuration synchronization
        // where the module that provides the field type is also being uninstalled.
        $field_storage_ids = [];
        foreach ($deletes as $config_name) {
            $field_storage_config_prefix = \Drupal::entityTypeManager()->getDefinition('field_storage_config')
                ->getConfigPrefix();
            if (strpos($config_name, $field_storage_config_prefix . '.') === 0) {
                $field_storage_ids[] = ConfigEntityStorage::getIDFromConfigName($config_name, $field_storage_config_prefix);
            }
        }
        if (!empty($field_storage_ids)) {
            $field_storages = \Drupal::entityQuery('field_storage_config')->condition('id', $field_storage_ids, 'IN')
                ->condition('module', $providers, 'NOT IN')
                ->execute();
            if (!empty($field_storages)) {
                $storages_to_delete = FieldStorageConfig::loadMultiple($field_storages);
            }
        }
        // Gather deleted fields from modules that are being uninstalled.
        
        /** @var \Drupal\field\FieldStorageConfigInterface[] $deleted_storage_definitions */
        $deleted_storage_definitions = \Drupal::service('entity_field.deleted_fields_repository')->getFieldStorageDefinitions();
        foreach ($deleted_storage_definitions as $field_storage_definition) {
            if ($field_storage_definition instanceof FieldStorageConfigInterface && !in_array($field_storage_definition->getTypeProvider(), $providers)) {
                $storages_to_delete[$field_storage_definition->id()] = $field_storage_definition;
            }
        }
        return $storages_to_delete;
    }

}