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 &$assignment) {
            uasort($assignment, 'Drupal\\block\\Entity\\Block::sort');
        }
        return $assignments;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getUniqueMachineName(string $suggestion, ?string $theme = NULL) : string {
        if ($theme) {
            $suggestion = $theme . '_' . $suggestion;
        }
        // Get all the block machine names that begin with the suggested string.
        $query = $this->blockStorage
            ->getQuery();
        $query->accessCheck(FALSE);
        $query->condition('id', $suggestion, 'CONTAINS');
        $block_ids = $query->execute();
        $block_ids = array_map(function ($block_id) {
            $parts = explode('.', $block_id);
            return end($parts);
        }, $block_ids);
        // Iterate through potential IDs until we get a new one. E.g.
        // For example, 'plugin', 'plugin_2', 'plugin_3', etc.
        $count = 1;
        $machine_default = $suggestion;
        while (in_array($machine_default, $block_ids)) {
            $machine_default = $suggestion . '_' . ++$count;
        }
        return $machine_default;
    }

}