class BlockRepository

class BlockRepository implements BlockRepositoryInterface {
    
    /**
     * The block storage.
     *
     * @var \Drupal\Core\Entity\EntityStorageInterface
     */
    protected $blockStorage;
    
    /**
     * The theme manager.
     *
     * @var \Drupal\Core\Theme\ThemeManagerInterface
     */
    protected $themeManager;
    
    /**
     * The context handler.
     *
     * @var \Drupal\Core\Plugin\Context\ContextHandlerInterface
     */
    protected $contextHandler;
    
    /**
     * Constructs a new BlockRepository.
     *
     * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
     *   The entity type manager service.
     * @param \Drupal\Core\Theme\ThemeManagerInterface $theme_manager
     *   The theme manager.
     * @param \Drupal\Core\Plugin\Context\ContextHandlerInterface $context_handler
     *   The plugin context handler.
     */
    public function __construct(EntityTypeManagerInterface $entity_type_manager, ThemeManagerInterface $theme_manager, ContextHandlerInterface $context_handler) {
        $this->blockStorage = $entity_type_manager->getStorage('block');
        $this->themeManager = $theme_manager;
        $this->contextHandler = $context_handler;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getVisibleBlocksPerRegion(array &$cacheable_metadata = []) {
        $active_theme = $this->themeManager
            ->getActiveTheme();
        // Build an array of the region names in the right order.
        $empty = array_fill_keys($active_theme->getRegions(), []);
        $full = [];
        foreach ($this->blockStorage
            ->loadByProperties([
            'theme' => $active_theme->getName(),
        ]) as $block_id => $block) {
            
            /** @var \Drupal\block\BlockInterface $block */
            $access = $block->access('view', NULL, TRUE);
            $region = $block->getRegion();
            if (!isset($cacheable_metadata[$region])) {
                $cacheable_metadata[$region] = CacheableMetadata::createFromObject($access);
            }
            else {
                $cacheable_metadata[$region] = $cacheable_metadata[$region]->merge(CacheableMetadata::createFromObject($access));
            }
            // Set the contexts on the block before checking access.
            if ($access->isAllowed()) {
                $full[$region][$block_id] = $block;
            }
        }
        // Merge it with the actual values to maintain the region ordering.
        $assignments = array_intersect_key(array_merge($empty, $full), $empty);
        foreach ($assignments as &$assignment) {
            // Suppress errors because PHPUnit will indirectly modify the contents,
            // triggering https://bugs.php.net/bug.php?id=50688.
            @uasort($assignment, 'Drupal\\block\\Entity\\Block::sort');
        }
        return $assignments;
    }

}