class TermStorage

class TermStorage extends SqlContentEntityStorage implements TermStorageInterface {
    
    /**
     * Array of term parents keyed by vocabulary ID and child term ID.
     *
     * @var array
     */
    protected $treeParents = [];
    
    /**
     * Array of term ancestors keyed by vocabulary ID and parent term ID.
     *
     * @var array
     */
    protected $treeChildren = [];
    
    /**
     * Array of terms in a tree keyed by vocabulary ID and term ID.
     *
     * @var array
     */
    protected $treeTerms = [];
    
    /**
     * Array of loaded trees keyed by a cache id matching tree arguments.
     *
     * @var array
     */
    protected $trees = [];
    
    /**
     * Array of all loaded term ancestry keyed by ancestor term ID, keyed by term
     * ID.
     *
     * @var \Drupal\taxonomy\TermInterface[][]
     */
    protected $ancestors;
    
    /**
     * The type of hierarchy allowed within a vocabulary.
     *
     * Possible values:
     * - VocabularyInterface::HIERARCHY_DISABLED: No parents.
     * - VocabularyInterface::HIERARCHY_SINGLE: Single parent.
     * - VocabularyInterface::HIERARCHY_MULTIPLE: Multiple parents.
     *
     * @var int[]
     *   An array of one the possible values above, keyed by vocabulary ID.
     */
    protected $vocabularyHierarchyType;
    
    /**
     * {@inheritdoc}
     *
     * @param array $values
     *   An array of values to set, keyed by property name. A value for the
     *   vocabulary ID ('vid') is required.
     */
    public function create(array $values = []) {
        // Save new terms with no parents by default.
        if (empty($values['parent'])) {
            $values['parent'] = [
                0,
            ];
        }
        $entity = parent::create($values);
        return $entity;
    }
    
    /**
     * {@inheritdoc}
     */
    public function resetCache(array $ids = NULL) {
        drupal_static_reset('taxonomy_term_count_nodes');
        $this->ancestors = [];
        $this->treeChildren = [];
        $this->treeParents = [];
        $this->treeTerms = [];
        $this->trees = [];
        $this->vocabularyHierarchyType = [];
        parent::resetCache($ids);
    }
    
    /**
     * {@inheritdoc}
     */
    public function deleteTermHierarchy($tids) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function updateTermHierarchy(EntityInterface $term) {
    }
    
    /**
     * {@inheritdoc}
     */
    public function loadParents($tid) {
        $terms = [];
        
        /** @var \Drupal\taxonomy\TermInterface $term */
        if ($tid && ($term = $this->load($tid))) {
            foreach ($this->getParents($term) as $id => $parent) {
                // This method currently doesn't return the <root> parent.
                // @see https://www.drupal.org/node/2019905
                if (!empty($id)) {
                    $terms[$id] = $parent;
                }
            }
        }
        return $terms;
    }
    
    /**
     * Returns a list of parents of this term.
     *
     * @return \Drupal\taxonomy\TermInterface[]
     *   The parent taxonomy term entities keyed by term ID. If this term has a
     *   <root> parent, that item is keyed with 0 and will have NULL as value.
     *
     * @internal
     * @todo Refactor away when TreeInterface is introduced.
     */
    protected function getParents(TermInterface $term) {
        $parents = $ids = [];
        // Cannot use $this->get('parent')->referencedEntities() here because that
        // strips out the '0' reference.
        foreach ($term->get('parent') as $item) {
            if ($item->target_id == 0) {
                // The <root> parent.
                $parents[0] = NULL;
                continue;
            }
            $ids[] = $item->target_id;
        }
        // @todo Better way to do this? AND handle the NULL/0 parent?
        // Querying the terms again so that the same access checks are run when
        // getParents() is called as in Drupal version prior to 8.3.
        $loaded_parents = [];
        if ($ids) {
            $query = \Drupal::entityQuery('taxonomy_term')->condition('tid', $ids, 'IN');
            $loaded_parents = static::loadMultiple($query->execute());
        }
        return $parents + $loaded_parents;
    }
    
    /**
     * {@inheritdoc}
     */
    public function loadAllParents($tid) {
        
        /** @var \Drupal\taxonomy\TermInterface $term */
        return !empty($tid) && ($term = $this->load($tid)) ? $this->getAncestors($term) : [];
    }
    
    /**
     * Returns all ancestors of this term.
     *
     * @return \Drupal\taxonomy\TermInterface[]
     *   A list of ancestor taxonomy term entities keyed by term ID.
     *
     * @internal
     * @todo Refactor away when TreeInterface is introduced.
     */
    protected function getAncestors(TermInterface $term) {
        if (!isset($this->ancestors[$term->id()])) {
            $this->ancestors[$term->id()] = [
                $term->id() => $term,
            ];
            $search[] = $term->id();
            while ($tid = array_shift($search)) {
                foreach ($this->getParents(static::load($tid)) as $id => $parent) {
                    if ($parent && !isset($this->ancestors[$term->id()][$id])) {
                        $this->ancestors[$term->id()][$id] = $parent;
                        $search[] = $id;
                    }
                }
            }
        }
        return $this->ancestors[$term->id()];
    }
    
    /**
     * {@inheritdoc}
     */
    public function loadChildren($tid, $vid = NULL) {
        
        /** @var \Drupal\taxonomy\TermInterface $term */
        return !empty($tid) && ($term = $this->load($tid)) ? $this->getChildren($term) : [];
    }
    
    /**
     * Returns all children terms of this term.
     *
     * @return \Drupal\taxonomy\TermInterface[]
     *   A list of children taxonomy term entities keyed by term ID.
     *
     * @internal
     * @todo Refactor away when TreeInterface is introduced.
     */
    public function getChildren(TermInterface $term) {
        $query = \Drupal::entityQuery('taxonomy_term')->condition('parent', $term->id());
        return static::loadMultiple($query->execute());
    }
    
    /**
     * {@inheritdoc}
     */
    public function loadTree($vid, $parent = 0, $max_depth = NULL, $load_entities = FALSE) {
        $cache_key = implode(':', func_get_args());
        if (!isset($this->trees[$cache_key])) {
            // We cache trees, so it's not CPU-intensive to call on a term and its
            // children, too.
            if (!isset($this->treeChildren[$vid])) {
                $this->treeChildren[$vid] = [];
                $this->treeParents[$vid] = [];
                $this->treeTerms[$vid] = [];
                $query = $this->database
                    ->select($this->getDataTable(), 't');
                $query->join('taxonomy_term__parent', 'p', 't.tid = p.entity_id');
                $query->addExpression('parent_target_id', 'parent');
                $result = $query->addTag('taxonomy_term_access')
                    ->fields('t')
                    ->condition('t.vid', $vid)
                    ->condition('t.default_langcode', 1)
                    ->orderBy('t.weight')
                    ->orderBy('t.name')
                    ->execute();
                foreach ($result as $term) {
                    $this->treeChildren[$vid][$term->parent][] = $term->tid;
                    $this->treeParents[$vid][$term->tid][] = $term->parent;
                    $this->treeTerms[$vid][$term->tid] = $term;
                }
            }
            // Load full entities, if necessary. The entity controller statically
            // caches the results.
            $term_entities = [];
            if ($load_entities) {
                $term_entities = $this->loadMultiple(array_keys($this->treeTerms[$vid]));
            }
            $max_depth = !isset($max_depth) ? count($this->treeChildren[$vid]) : $max_depth;
            $tree = [];
            // Keeps track of the parents we have to process, the last entry is used
            // for the next processing step.
            $process_parents = [];
            $process_parents[] = $parent;
            // Loops over the parent terms and adds its children to the tree array.
            // Uses a loop instead of a recursion, because it's more efficient.
            while (count($process_parents)) {
                $parent = array_pop($process_parents);
                // The number of parents determines the current depth.
                $depth = count($process_parents);
                if ($max_depth > $depth && !empty($this->treeChildren[$vid][$parent])) {
                    $has_children = FALSE;
                    $child = current($this->treeChildren[$vid][$parent]);
                    do {
                        if (empty($child)) {
                            break;
                        }
                        $term = $load_entities ? $term_entities[$child] : $this->treeTerms[$vid][$child];
                        if (isset($this->treeParents[$vid][$load_entities ? $term->id() : $term->tid])) {
                            // Clone the term so that the depth attribute remains correct
                            // in the event of multiple parents.
                            $term = clone $term;
                        }
                        $term->depth = $depth;
                        if (!$load_entities) {
                            unset($term->parent);
                        }
                        $tid = $load_entities ? $term->id() : $term->tid;
                        $term->parents = $this->treeParents[$vid][$tid];
                        $tree[] = $term;
                        if (!empty($this->treeChildren[$vid][$tid])) {
                            $has_children = TRUE;
                            // We have to continue with this parent later.
                            $process_parents[] = $parent;
                            // Use the current term as parent for the next iteration.
                            $process_parents[] = $tid;
                            // Reset pointers for child lists because we step in there more
                            // often with multi parents.
                            reset($this->treeChildren[$vid][$tid]);
                            // Move pointer so that we get the correct term the next time.
                            next($this->treeChildren[$vid][$parent]);
                            break;
                        }
                    } while ($child = next($this->treeChildren[$vid][$parent]));
                    if (!$has_children) {
                        // We processed all terms in this hierarchy-level, reset pointer
                        // so that this function works the next time it gets called.
                        reset($this->treeChildren[$vid][$parent]);
                    }
                }
            }
            $this->trees[$cache_key] = $tree;
        }
        return $this->trees[$cache_key];
    }
    
    /**
     * {@inheritdoc}
     */
    public function nodeCount($vid) {
        $query = $this->database
            ->select('taxonomy_index', 'ti');
        $query->addExpression('COUNT(DISTINCT ti.nid)');
        $query->leftJoin($this->getBaseTable(), 'td', 'ti.tid = td.tid');
        $query->condition('td.vid', $vid);
        $query->addTag('vocabulary_node_count');
        return $query->execute()
            ->fetchField();
    }
    
    /**
     * {@inheritdoc}
     */
    public function resetWeights($vid) {
        $this->database
            ->update($this->getDataTable())
            ->fields([
            'weight' => 0,
        ])
            ->condition('vid', $vid)
            ->execute();
    }
    
    /**
     * {@inheritdoc}
     */
    public function getNodeTerms(array $nids, array $vocabs = [], $langcode = NULL) {
        $query = $this->database
            ->select($this->getDataTable(), 'td');
        $query->innerJoin('taxonomy_index', 'tn', 'td.tid = tn.tid');
        $query->fields('td', [
            'tid',
        ]);
        $query->addField('tn', 'nid', 'node_nid');
        $query->orderby('td.weight');
        $query->orderby('td.name');
        $query->condition('tn.nid', $nids, 'IN');
        $query->addTag('taxonomy_term_access');
        if (!empty($vocabs)) {
            $query->condition('td.vid', $vocabs, 'IN');
        }
        if (!empty($langcode)) {
            $query->condition('td.langcode', $langcode);
        }
        $results = [];
        $all_tids = [];
        foreach ($query->execute() as $term_record) {
            $results[$term_record->node_nid][] = $term_record->tid;
            $all_tids[] = $term_record->tid;
        }
        $all_terms = $this->loadMultiple($all_tids);
        $terms = [];
        foreach ($results as $nid => $tids) {
            foreach ($tids as $tid) {
                $terms[$nid][$tid] = $all_terms[$tid];
            }
        }
        return $terms;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getTermIdsWithPendingRevisions() {
        $table_mapping = $this->getTableMapping();
        $id_field = $table_mapping->getColumnNames($this->entityType
            ->getKey('id'))['value'];
        $revision_field = $table_mapping->getColumnNames($this->entityType
            ->getKey('revision'))['value'];
        $rta_field = $table_mapping->getColumnNames($this->entityType
            ->getKey('revision_translation_affected'))['value'];
        $langcode_field = $table_mapping->getColumnNames($this->entityType
            ->getKey('langcode'))['value'];
        $revision_default_field = $table_mapping->getColumnNames($this->entityType
            ->getRevisionMetadataKey('revision_default'))['value'];
        $query = $this->database
            ->select($this->getRevisionDataTable(), 'tfr');
        $query->fields('tfr', [
            $id_field,
        ]);
        $query->addExpression("MAX(tfr.{$revision_field})", $revision_field);
        $query->join($this->getRevisionTable(), 'tr', "tfr.{$revision_field} = tr.{$revision_field} AND tr.{$revision_default_field} = 0");
        $inner_select = $this->database
            ->select($this->getRevisionDataTable(), 't');
        $inner_select->condition("t.{$rta_field}", '1');
        $inner_select->fields('t', [
            $id_field,
            $langcode_field,
        ]);
        $inner_select->addExpression("MAX(t.{$revision_field})", $revision_field);
        $inner_select->groupBy("t.{$id_field}")
            ->groupBy("t.{$langcode_field}");
        $query->join($inner_select, 'mr', "tfr.{$revision_field} = mr.{$revision_field} AND tfr.{$langcode_field} = mr.{$langcode_field}");
        $query->groupBy("tfr.{$id_field}");
        return $query->execute()
            ->fetchAllKeyed(1, 0);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getVocabularyHierarchyType($vid) {
        // Return early if we already computed this value.
        if (isset($this->vocabularyHierarchyType[$vid])) {
            return $this->vocabularyHierarchyType[$vid];
        }
        $parent_field_storage = $this->entityFieldManager
            ->getFieldStorageDefinitions($this->entityTypeId)['parent'];
        $table_mapping = $this->getTableMapping();
        $target_id_column = $table_mapping->getFieldColumnName($parent_field_storage, 'target_id');
        $delta_column = $table_mapping->getFieldColumnName($parent_field_storage, TableMappingInterface::DELTA);
        $query = $this->database
            ->select($table_mapping->getFieldTableName('parent'), 'p');
        $query->addExpression("MAX({$target_id_column})", 'max_parent_id');
        $query->addExpression("MAX({$delta_column})", 'max_delta');
        $query->condition('bundle', $vid);
        $result = $query->execute()
            ->fetchAll();
        // If all the terms have the same parent, the parent can only be root (0).
        if ((int) $result[0]->max_parent_id === 0) {
            $this->vocabularyHierarchyType[$vid] = VocabularyInterface::HIERARCHY_DISABLED;
        }
        elseif ((int) $result[0]->max_delta === 0) {
            $this->vocabularyHierarchyType[$vid] = VocabularyInterface::HIERARCHY_SINGLE;
        }
        else {
            $this->vocabularyHierarchyType[$vid] = VocabularyInterface::HIERARCHY_MULTIPLE;
        }
        return $this->vocabularyHierarchyType[$vid];
    }
    
    /**
     * {@inheritdoc}
     */
    public function __sleep() {
        $vars = parent::__sleep();
        // Do not serialize static cache.
        unset($vars['ancestors'], $vars['treeChildren'], $vars['treeParents'], $vars['treeTerms'], $vars['trees'], $vars['vocabularyHierarchyType']);
        return $vars;
    }
    
    /**
     * {@inheritdoc}
     */
    public function __wakeup() {
        parent::__wakeup();
        // Initialize static caches.
        $this->ancestors = [];
        $this->treeChildren = [];
        $this->treeParents = [];
        $this->treeTerms = [];
        $this->trees = [];
        $this->vocabularyHierarchyType = [];
    }

}