Drupal 8 batch opertation

BatchController.php

<?php
namespace Drupal\my_module\Controller;

use Drupal\Core\Controller\ControllerBase;
use Drupal\Core\Url;

class BatchProcessController extends ControllerBase
{

  const OPERATION_CREATE = 0;
  const OPERATION_UPDATE = 1;
  const OPERATION_DELETE = 2;
  
  /**
   * Finish batch.
   */
  public static function finishBatch($success, $results, $operations)
  {
    // @todo we can use here the $results for displaying further information
    if ($success) {
      if (!empty($results['errors'])) {
        foreach ($results['errors'] as $error) {
          drupal_set_message($error, 'error');
          \Drupal::logger('json_migrate')->error($error);
        }
        drupal_set_message(\Drupal::translation()
          ->translate('The content was imported with errors.'), 'warning');
      }
      else {
        drupal_set_message(\Drupal::translation()
          ->translate('The content was imported successfully.'));
      }
    }
    else {
      // An error occurred.
      // $operations contains the operations that remained unprocessed.
      $error_operation = reset($operations);
      $message = \Drupal::translation()
        ->translate('An error occurred while processing %error_operation with arguments: @arguments', array(
          '%error_operation' => $error_operation[0],
          '@arguments' => print_r($error_operation[1], TRUE)
        ));
      drupal_set_message($message, 'error');
    }
  }
  
  /**
   * Merely displays a message, should be used for other purpose.
   * @return array
   */
  public function getResults()
  {
    return array(
      '#type' => 'markup',
      '#markup' => $this->t('Batch process finished'),
    );
  }

  /**
   * Processes the batch.
   *
   * @param int $amount
   *  Count of the contents.
   * @param int $operation
   *  Current operation to run the batch on.
   * @param string $content
   *   The content to import.
   * @param array $context
   *   The batch context.
   */
  public static function processBatch($amount, $operation, $content, &$context)
  {
    //@todo process here the heavy work on the content

    // cannot use dependency injection an need static call from a static context
    \Drupal::logger('json_migrate')->info(
      \Drupal::translation()
        ->translate('Imported content %content', array('%content' => $content))
    );
    //    review e.g. \Drupal\migrate_drupal_ui\MigrateUpgradeRunBatch
    //    if (!isset($context['sandbox']['current'])) {
    //      $context['sandbox']['current_id'] = $content->id; // @todo get id, e.g. nid
    //      $context['sandbox']['max'] = $amount;
    //      $context['sandbox']['num_processed'] = 0;
    //      $context['sandbox']['messages'] = [];
    //      $context['results']['failures'] = 0;
    //      $context['results']['successes'] = 0;
    //      $context['results']['operation'] = $operation;
    //    }
    //    else {
    //      $context['sandbox']['current_id'] = $content->id; // @todo get id, e.g. nid
    //      $context['sandbox']['num_processed']++;
    //      $context['results']['failures'] = 0; // @todo fetched from the result
    //      $context['sandbox']['messages'][] = ''; // @todo optional message
    //      $context['results']['successes']++; // @todo fetched from the result
    //    }

    //    Store some result for post-processing in the finished callback.
    //    $context['results'][] = $content;
    //    $context['message'] = t('Now processing %node', array('%node' => $content));

    //    if ($errors = $myWorkerClass->getErrors()) {
    //      if (!isset($context['results']['errors'])) {
    //        $context['results']['errors'] = array();
    //      }
    //      $context['results']['errors'] += $errors;
    //    }
  }

  public function initBatch()
  {
    try {
      // a list of contents to process
      $contentToMigrate = array(
        1,
        2,
        3,
        4,
        5
      );
      $batch = [
        'operations' => [],
        'finished' => [BatchFinishController::class, 'finishBatch'],
        'title' => $this->t('Migrating content'),
        'init_message' => $this->t('Starting content migration.'),
        'progress_message' => $this->t('Completed @current step of @total.'),
        'error_message' => $this->t('Content migration has encountered an error.'),
      ];
      $amount = count($contentToMigrate);
      $operation = BatchProcessController::OPERATION_CREATE;
      foreach ($contentToMigrate as $content) {
        $batch['operations'][] = [
          [get_class($this), 'processBatch'],
          [$amount, $operation, $content]
        ];
      }
      batch_set($batch);
    } // @todo custom exception
    catch (\Exception $e) {
      drupal_set_message($e->getMessage(), 'error');
    }

    $url = Url::fromRoute('json_migrate.batch_finish');
    return batch_process($url);
  }
}

my_module.routing.yml

my_module.batch_process:
  path: '/admin/my_module/batch/process'
  defaults:
    _controller: '\Drupal\my_module\Controller\BatchController::initBatch'
    _title: 'Batch init'
  requirements:
    _permission: 'administer site configuration'

my_module.batch_finish:
  path: '/admin/my_module/batch/finish'
  defaults:
    _controller: '\Drupal\my_module\Controller\BatchController::getResults'
    _title: 'Batch results'
  requirements:
    _permission: 'administer site configuration'