class QueryBase

abstract class QueryBase implements QueryInterface {
    
    /**
     * The entity type this query runs against.
     *
     * @var string
     */
    protected $entityTypeId;
    
    /**
     * Information about the entity type.
     *
     * @var \Drupal\Core\Entity\EntityTypeInterface
     */
    protected $entityType;
    
    /**
     * The list of sorts.
     *
     * @var array
     */
    protected $sort = [];
    
    /**
     * TRUE if this is a count query, FALSE if it isn't.
     *
     * @var bool
     */
    protected $count = FALSE;
    
    /**
     * Conditions.
     *
     * @var \Drupal\Core\Entity\Query\ConditionInterface
     */
    protected $condition;
    
    /**
     * The list of aggregate expressions.
     *
     * @var array
     */
    protected $aggregate = [];
    
    /**
     * The list of columns to group on.
     *
     * @var array
     */
    protected $groupBy = [];
    
    /**
     * Aggregate Conditions.
     *
     * @var \Drupal\Core\Entity\Query\ConditionAggregateInterface
     */
    protected $conditionAggregate;
    
    /**
     * The list of sorts over the aggregate results.
     *
     * @var array
     */
    protected $sortAggregate = [];
    
    /**
     * The query range.
     *
     * @var array
     */
    protected $range = [];
    
    /**
     * The query metadata for alter purposes.
     *
     * @var array
     */
    protected $alterMetaData;
    
    /**
     * The query tags.
     *
     * @var array
     */
    protected $alterTags;
    
    /**
     * Whether access check is requested or not.
     *
     * @var bool|null
     */
    protected $accessCheck;
    
    /**
     * Flag indicating whether to query the current revision or all revisions.
     *
     * @var bool
     */
    protected $allRevisions = FALSE;
    
    /**
     * Flag indicating whether to query the latest revision.
     *
     * @var bool
     */
    protected $latestRevision = FALSE;
    
    /**
     * The query pager data.
     *
     * @var array
     *
     * @see Query::pager()
     */
    protected $pager = [];
    
    /**
     * List of potential namespaces of the classes belonging to this query.
     *
     * @var array
     */
    protected $namespaces = [];
    
    /**
     * Defines how the conditions on the query need to match.
     */
    protected $conjunction;
    
    /**
     * Constructs this object.
     *
     * @param \Drupal\Core\Entity\EntityTypeInterface $entity_type
     *   The entity type definition.
     * @param string $conjunction
     *   - AND: all of the conditions on the query need to match.
     *   - OR: at least one of the conditions on the query need to match.
     * @param array $namespaces
     *   List of potential namespaces of the classes belonging to this query.
     */
    public function __construct(EntityTypeInterface $entity_type, $conjunction, array $namespaces) {
        $this->entityTypeId = $entity_type->id();
        $this->entityType = $entity_type;
        $this->conjunction = $conjunction;
        $this->namespaces = $namespaces;
        $this->condition = $this->conditionGroupFactory($conjunction);
        if ($this instanceof QueryAggregateInterface) {
            $this->conditionAggregate = $this->conditionAggregateGroupFactory($conjunction);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function getEntityTypeId() {
        return $this->entityTypeId;
    }
    
    /**
     * {@inheritdoc}
     */
    public function condition($property, $value = NULL, $operator = NULL, $langcode = NULL) {
        $this->condition
            ->condition($property, $value, $operator, $langcode);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function exists($property, $langcode = NULL) {
        $this->condition
            ->exists($property, $langcode);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function notExists($property, $langcode = NULL) {
        $this->condition
            ->notExists($property, $langcode);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function range($start = NULL, $length = NULL) {
        $this->range = [
            'start' => $start,
            'length' => $length,
        ];
        return $this;
    }
    
    /**
     * Creates an object holding a group of conditions.
     *
     * See andConditionGroup() and orConditionGroup() for more.
     *
     * @param string $conjunction
     *   - AND (default): this is the equivalent of andConditionGroup().
     *   - OR: this is the equivalent of orConditionGroup().
     *
     * @return \Drupal\Core\Entity\Query\ConditionInterface
     *   An object holding a group of conditions.
     */
    protected function conditionGroupFactory($conjunction = 'AND') {
        $class = static::getClass($this->namespaces, 'Condition');
        return new $class($conjunction, $this, $this->namespaces);
    }
    
    /**
     * {@inheritdoc}
     */
    public function andConditionGroup() {
        return $this->conditionGroupFactory('and');
    }
    
    /**
     * {@inheritdoc}
     */
    public function orConditionGroup() {
        return $this->conditionGroupFactory('or');
    }
    
    /**
     * {@inheritdoc}
     */
    public function sort($field, $direction = 'ASC', $langcode = NULL) {
        $this->sort[] = [
            'field' => $field,
            'direction' => strtoupper($direction),
            'langcode' => $langcode,
        ];
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function count() {
        $this->count = TRUE;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function accessCheck($access_check = TRUE) {
        $this->accessCheck = $access_check;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function currentRevision() {
        $this->allRevisions = FALSE;
        $this->latestRevision = FALSE;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function latestRevision() {
        $this->allRevisions = TRUE;
        $this->latestRevision = TRUE;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function allRevisions() {
        $this->allRevisions = TRUE;
        $this->latestRevision = FALSE;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function pager($limit = 10, $element = NULL) {
        // Even when not using SQL, storing the element PagerSelectExtender is as
        // good as anywhere else.
        if (!isset($element)) {
            $element = \Drupal::service('pager.manager')->getMaxPagerElementId() + 1;
        }
        $this->pager = [
            'limit' => $limit,
            'element' => $element,
        ];
        return $this;
    }
    
    /**
     * Gets the total number of results and initialize a pager for the query.
     *
     * The pager can be disabled by either setting the pager limit to 0, or by
     * setting this query to be a count query.
     */
    protected function initializePager() {
        if ($this->pager && !empty($this->pager['limit']) && !$this->count) {
            $page = \Drupal::service('pager.parameters')->findPage($this->pager['element']);
            $count_query = clone $this;
            $this->pager['total'] = $count_query->count()
                ->execute();
            $this->pager['start'] = $page * $this->pager['limit'];
            \Drupal::service('pager.manager')->createPager($this->pager['total'], $this->pager['limit'], $this->pager['element']);
            $this->range($this->pager['start'], $this->pager['limit']);
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function tableSort(&$headers) {
        // If 'field' is not initialized, the header columns aren't clickable.
        foreach ($headers as $key => $header) {
            if (is_array($header) && isset($header['specifier'])) {
                $headers[$key]['field'] = '';
            }
        }
        $order = TableSort::getOrder($headers, \Drupal::request());
        $direction = TableSort::getSort($headers, \Drupal::request());
        foreach ($headers as $header) {
            if (is_array($header) && $header['data'] == $order['name']) {
                $this->sort($header['specifier'], $direction, $header['langcode'] ?? NULL);
            }
        }
        return $this;
    }
    
    /**
     * Makes sure that the Condition object is cloned as well.
     */
    public function __clone() {
        $this->condition = clone $this->condition;
    }
    
    /**
     * {@inheritdoc}
     */
    public function addTag($tag) {
        $this->alterTags[$tag] = 1;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasTag($tag) {
        return isset($this->alterTags[$tag]);
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasAllTags() {
        return !(bool) array_diff(func_get_args(), array_keys($this->alterTags));
    }
    
    /**
     * {@inheritdoc}
     */
    public function hasAnyTag() {
        return (bool) array_intersect(func_get_args(), array_keys($this->alterTags));
    }
    
    /**
     * {@inheritdoc}
     */
    public function addMetaData($key, $object) {
        $this->alterMetaData[$key] = $object;
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getMetaData($key) {
        return $this->alterMetaData[$key] ?? NULL;
    }
    
    /**
     * {@inheritdoc}
     */
    public function aggregate($field, $function, $langcode = NULL, &$alias = NULL) {
        if (!isset($alias)) {
            $alias = $this->getAggregationAlias($field, $function);
        }
        $this->aggregate[$alias] = [
            'field' => $field,
            'function' => $function,
            'alias' => $alias,
            'langcode' => $langcode,
        ];
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function conditionAggregate($field, $function = NULL, $value = NULL, $operator = '=', $langcode = NULL) {
        $this->aggregate($field, $function, $langcode);
        $this->conditionAggregate
            ->condition($field, $function, $value, $operator, $langcode);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function sortAggregate($field, $function, $direction = 'ASC', $langcode = NULL) {
        $alias = $this->getAggregationAlias($field, $function);
        $this->sortAggregate[$alias] = [
            'field' => $field,
            'function' => $function,
            'direction' => $direction,
            'langcode' => $langcode,
        ];
        $this->aggregate($field, $function, $langcode, $alias);
        return $this;
    }
    
    /**
     * {@inheritdoc}
     */
    public function groupBy($field, $langcode = NULL) {
        $this->groupBy[] = [
            'field' => $field,
            'langcode' => $langcode,
        ];
        return $this;
    }
    
    /**
     * Generates an alias for a field and its aggregated function.
     *
     * @param string $field
     *   The field name used in the alias.
     * @param string $function
     *   The aggregation function used in the alias.
     *
     * @return string
     *   The alias for the field.
     */
    protected function getAggregationAlias($field, $function) {
        return strtolower($field . '_' . $function);
    }
    
    /**
     * Gets a list of namespaces of the ancestors of a class.
     *
     * @param $object
     *   An object within a namespace.
     *
     * @return array
     *   A list containing the namespace of the class, the namespace of the
     *   parent of the class and so on and so on.
     */
    public static function getNamespaces($object) {
        $namespaces = [];
        for ($class = get_class($object); $class; $class = get_parent_class($class)) {
            $namespaces[] = substr($class, 0, strrpos($class, '\\'));
        }
        return $namespaces;
    }
    
    /**
     * Finds a class in a list of namespaces.
     *
     * @param array $namespaces
     *   A list of namespaces.
     * @param string $short_class_name
     *   A class name without namespace.
     *
     * @return string
     *   The fully qualified name of the class.
     */
    public static function getClass(array $namespaces, $short_class_name) {
        foreach ($namespaces as $namespace) {
            $class = $namespace . '\\' . $short_class_name;
            if (class_exists($class)) {
                return $class;
            }
        }
    }

}