Drupal 8 file upload block

SiteLogoBlock.php

<?php

namespace Drupal\mymodule\Plugin\Block;

use Drupal\Core\Block\BlockBase;
use Drupal\Core\Form\FormStateInterface;
use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
use Drupal\file\Entity\File;
use Drupal\file\FileUsage\FileUsageInterface;
use Symfony\Component\DependencyInjection\ContainerInterface;

/**
 * Provides a 'Site Logo' Block.
 *
 * @Block(
 *   id = "mymodule_site_logo_block",
 *   admin_label = @Translation("Site Logo"),
 *   category = @Translation("Custom"),
 * )
 */
class SiteLogoBlock extends BlockBase implements ContainerFactoryPluginInterface {

  /**
   * The file usage interface.
   *
   * @var \Drupal\file\FileUsage\FileUsageInterface
   */
  protected $fileUsage;

  /**
   * SiteLogoBlock constructor.
   *
   * @param array $configuration
   *   A configuration array containing information about the plugin instance.
   * @param string $plugin_id
   *   The plugin_id for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\file\FileUsage\FileUsageInterface $file_usage
   *   File usage interface.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, FileUsageInterface $file_usage) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->fileUsage = $file_usage;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static(
      $configuration,
      $plugin_id,
      $plugin_definition,
      $container->get('file.usage')
    );
  }

  /**
   * {@inheritdoc}
   */
  public function defaultConfiguration() {
    return [
      'label_display' => FALSE,
      'primary_logo' => '',
      'secondary_logo' => '',
    ];
  }

  /**
   * {@inheritdoc}
   */
  public function blockForm($form, FormStateInterface $form_state) {

    $form['logos'] = [
      '#type' => 'fieldset',
      '#title' => $this->t('Logos'),
    ];

    $primary_logo = $this->configuration['primary_logo'];
    $form['logos']['primary_logo'] = [
      '#type' => 'managed_file',
      '#title' => $this->t('Primary Logo'),
      '#default_value' => $primary_logo,
      '#upload_location' => 'public://site-logo/',
      '#upload_validators' => [
        'file_validate_extensions' => ['png'],
      ],
      '#description' => $this->t('Allowed extensions: png'),
    ];

    $form['logos']['primary_logo_fid_exists'] = [
      '#type' => 'value',
      '#value' => isset($primary_logo[0]) ? $primary_logo[0] : FALSE,
    ];

    $secondary_logo = $this->configuration['secondary_logo'];
    $form['logos']['secondary_logo'] = [
      '#type' => 'managed_file',
      '#title' => $this->t('Secondary Logo'),
      '#default_value' => $secondary_logo,
      '#upload_location' => 'public://site-logo/',
      '#upload_validators' => [
        'file_validate_extensions' => ['png'],
      ],
      '#description' => $this->t('Allowed extensions: png'),
    ];

    $form['logos']['secondary_logo_fid_exists'] = [
      '#type' => 'value',
      '#value' => isset($secondary_logo[0]) ? $secondary_logo[0] : FALSE,
    ];

    return $form;
  }

  /**
   * {@inheritdoc}
   */
  public function blockSubmit($form, FormStateInterface $form_state) {

    $logos = [
      'primary_logo',
      'secondary_logo',
    ];

    foreach ($logos as $logo) {
      // 1. Get form value and save it.
      $image = $form_state->getValue(['logos', $logo]);
      $this->configuration[$logo] = $image;

      // 2. Handle file upload.
      /** @var \Drupal\file\FileUsage\FileUsageInterface $file_usage */
      $file_usage = $this->fileUsage;
      if ($file_id = isset($image[0]) ? $image[0] : FALSE) {
        /** @var \Drupal\file\Entity\File $file */
        $file = File::load($file_id);
        $file->setPermanent();
        $file->save();
        $file_usage->add($file, 'ix_header', 'ix_header', $file->id());
      }
      if ($existing_fid = $form_state->getValue(['logos', "{$logo}_fid_exists",])) {
        /** @var \Drupal\file\Entity\File $existing_file */
        $existing_file = File::load($existing_fid);
        if ($existing_fid !== $file_id) {
          $file_usage->delete($existing_file, 'ix_header', 'ix_header', $existing_file->id(), 0);
        }
      }
    }
  }

  /**
   * {@inheritdoc}
   */
  public function build() {

    // mymodule/templates/mymodule-site-logo.html.twig.
    return [
      '#theme' => 'mymodule_site_logo',
      // @todo Pass images to template and render.
      //'#primary_logo' => $this->configuration['primary_logo'],
      //'#secondary_logo' => $this->configuration['secondary_logo'],
      '#primary_logo' => [],
      '#secondary_logo' => [],
    ];
  }

}