class Query

class Query extends QueryBase implements QueryInterface {
    
    /**
     * The build sql select query.
     *
     * @var \Drupal\Core\Database\Query\SelectInterface
     */
    protected $sqlQuery;
    
    /**
     * The Tables object for this query.
     *
     * @var \Drupal\Core\Entity\Query\Sql\TablesInterface
     */
    protected $tables;
    
    /**
     * An array of fields keyed by the field alias.
     *
     * Each entry correlates to the arguments of
     * \Drupal\Core\Database\Query\SelectInterface::addField(), so the first one
     * is the table alias, the second one the field and the last one optional the
     * field alias.
     *
     * @var array
     */
    protected $sqlFields = [];
    
    /**
     * An array of strings added as to the group by, keyed by the string to avoid
     * duplicates.
     *
     * @var array
     */
    protected $sqlGroupBy = [];
    
    /**
     * @var \Drupal\Core\Database\Connection
     */
    protected $connection;
    
    /**
     * Constructs a query 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 \Drupal\Core\Database\Connection $connection
     *   The database connection to run the query against.
     * @param array $namespaces
     *   List of potential namespaces of the classes belonging to this query.
     */
    public function __construct(EntityTypeInterface $entity_type, $conjunction, Connection $connection, array $namespaces) {
        parent::__construct($entity_type, $conjunction, $namespaces);
        $this->connection = $connection;
    }
    
    /**
     * {@inheritdoc}
     */
    public function execute() {
        return $this->prepare()
            ->compile()
            ->addSort()
            ->finish()
            ->result();
    }
    
    /**
     * Prepares the basic query with proper metadata/tags and base fields.
     *
     * @return $this
     *   Returns the called object.
     *
     * @throws \Drupal\Core\Entity\Query\QueryException
     *   Thrown if the base table does not exist.
     */
    protected function prepare() {
        if ($this->allRevisions) {
            if (!($base_table = $this->entityType
                ->getRevisionTable())) {
                throw new QueryException("No revision table for " . $this->entityTypeId . ", invalid query.");
            }
        }
        else {
            if (!($base_table = $this->entityType
                ->getBaseTable())) {
                throw new QueryException("No base table for " . $this->entityTypeId . ", invalid query.");
            }
        }
        $simple_query = TRUE;
        if ($this->entityType
            ->getDataTable()) {
            $simple_query = FALSE;
        }
        $this->sqlQuery = $this->connection
            ->select($base_table, 'base_table', [
            'conjunction' => $this->conjunction,
        ]);
        // Reset the tables structure, as it might have been built for a previous
        // execution of this query.
        $this->tables = NULL;
        $this->sqlQuery
            ->addMetaData('entity_type', $this->entityTypeId);
        $id_field = $this->entityType
            ->getKey('id');
        // Add the key field for fetchAllKeyed().
        if (!($revision_field = $this->entityType
            ->getKey('revision'))) {
            // When there is no revision support, the key field is the entity key.
            $this->sqlFields["base_table.{$id_field}"] = [
                'base_table',
                $id_field,
            ];
            // Now add the value column for fetchAllKeyed(). This is always the
            // entity id.
            $this->sqlFields["base_table.{$id_field}" . '_1'] = [
                'base_table',
                $id_field,
            ];
        }
        else {
            // When there is revision support, the key field is the revision key.
            $this->sqlFields["base_table.{$revision_field}"] = [
                'base_table',
                $revision_field,
            ];
            // Now add the value column for fetchAllKeyed(). This is always the
            // entity id.
            $this->sqlFields["base_table.{$id_field}"] = [
                'base_table',
                $id_field,
            ];
        }
        // Add a self-join to the base revision table if we're querying only the
        // latest revisions.
        if ($this->latestRevision && $revision_field) {
            $this->sqlQuery
                ->leftJoin($base_table, 'base_table_2', "base_table.{$id_field} = base_table_2.{$id_field} AND base_table.{$revision_field} < base_table_2.{$revision_field}");
            $this->sqlQuery
                ->isNull("base_table_2.{$id_field}");
        }
        if ($this->accessCheck) {
            $this->sqlQuery
                ->addTag($this->entityTypeId . '_access');
        }
        $this->sqlQuery
            ->addTag('entity_query');
        $this->sqlQuery
            ->addTag('entity_query_' . $this->entityTypeId);
        // Add further tags added.
        if (isset($this->alterTags)) {
            foreach ($this->alterTags as $tag => $value) {
                $this->sqlQuery
                    ->addTag($tag);
            }
        }
        // Add further metadata added.
        if (isset($this->alterMetaData)) {
            foreach ($this->alterMetaData as $key => $value) {
                $this->sqlQuery
                    ->addMetaData($key, $value);
            }
        }
        // This now contains first the table containing entity properties and
        // last the entity base table. They might be the same.
        $this->sqlQuery
            ->addMetaData('all_revisions', $this->allRevisions);
        $this->sqlQuery
            ->addMetaData('simple_query', $simple_query);
        return $this;
    }
    
    /**
     * Compiles the conditions.
     *
     * @return $this
     *   Returns the called object.
     */
    protected function compile() {
        $this->condition
            ->compile($this->sqlQuery);
        return $this;
    }
    
    /**
     * Adds the sort to the build query.
     *
     * @return $this
     *   Returns the called object.
     */
    protected function addSort() {
        if ($this->count) {
            $this->sort = [];
        }
        // Gather the SQL field aliases first to make sure every field table
        // necessary is added. This might change whether the query is simple or
        // not. See below for more on simple queries.
        $sort = [];
        if ($this->sort) {
            foreach ($this->sort as $key => $data) {
                $sort[$key] = $this->getSqlField($data['field'], $data['langcode']);
            }
        }
        $simple_query = $this->isSimpleQuery();
        // If the query is set up for paging either via pager or by range or a
        // count is requested, then the correct amount of rows returned is
        // important. If the entity has a data table or multiple value fields are
        // involved then each revision might appear in several rows and this needs
        // a significantly more complex query.
        if (!$simple_query) {
            // First, GROUP BY revision id (if it has been added) and entity id.
            // Now each group contains a single revision of an entity.
            foreach ($this->sqlFields as $field) {
                $group_by = "{$field[0]}.{$field[1]}";
                $this->sqlGroupBy[$group_by] = $group_by;
            }
        }
        // Now we know whether this is a simple query or not, actually do the
        // sorting.
        foreach ($sort as $key => $sql_alias) {
            $direction = $this->sort[$key]['direction'];
            if ($simple_query || isset($this->sqlGroupBy[$sql_alias])) {
                // Simple queries, and the grouped columns of complicated queries
                // can be ordered normally, without the aggregation function.
                $this->sqlQuery
                    ->orderBy($sql_alias, $direction);
                if (!isset($this->sqlFields[$sql_alias])) {
                    $this->sqlFields[$sql_alias] = explode('.', $sql_alias);
                }
            }
            else {
                // Order based on the smallest element of each group if the
                // direction is ascending, or on the largest element of each group
                // if the direction is descending.
                $function = $direction == 'ASC' ? 'min' : 'max';
                $expression = "{$function}({$sql_alias})";
                $expression_alias = $this->sqlQuery
                    ->addExpression($expression);
                $this->sqlQuery
                    ->orderBy($expression_alias, $direction);
            }
        }
        return $this;
    }
    
    /**
     * Finish the query by adding fields, GROUP BY and range.
     *
     * @return $this
     *   Returns the called object.
     */
    protected function finish() {
        $this->initializePager();
        if ($this->range) {
            $this->sqlQuery
                ->range($this->range['start'], $this->range['length']);
        }
        foreach ($this->sqlGroupBy as $field) {
            $this->sqlQuery
                ->groupBy($field);
        }
        foreach ($this->sqlFields as $field) {
            $this->sqlQuery
                ->addField($field[0], $field[1], isset($field[2]) ? $field[2] : NULL);
        }
        return $this;
    }
    
    /**
     * Executes the query and returns the result.
     *
     * @return int|array
     *   Returns the query result as entity IDs.
     */
    protected function result() {
        if ($this->count) {
            return $this->sqlQuery
                ->countQuery()
                ->execute()
                ->fetchField();
        }
        // Return a keyed array of results. The key is either the revision_id or
        // the entity_id depending on whether the entity type supports revisions.
        // The value is always the entity id.
        return $this->sqlQuery
            ->execute()
            ->fetchAllKeyed();
    }
    
    /**
     * Constructs a select expression for a given field and language.
     *
     * @param string $field
     *   The name of the field being queried.
     * @param string $langcode
     *   The language code of the field.
     *
     * @return string
     *   An expression that will select the given field for the given language in
     *   a SELECT query, such as 'base_table.id'.
     */
    protected function getSqlField($field, $langcode) {
        if (!isset($this->tables)) {
            $this->tables = $this->getTables($this->sqlQuery);
        }
        $base_property = "base_table.{$field}";
        if (isset($this->sqlFields[$base_property])) {
            return $base_property;
        }
        else {
            return $this->tables
                ->addField($field, 'LEFT', $langcode);
        }
    }
    
    /**
     * Determines whether the query requires GROUP BY and ORDER BY MIN/MAX.
     *
     * @return bool
     */
    protected function isSimpleQuery() {
        return !$this->pager && !$this->range && !$this->count || $this->sqlQuery
            ->getMetaData('simple_query');
    }
    
    /**
     * Implements the magic __clone method.
     *
     * Reset fields and GROUP BY when cloning.
     */
    public function __clone() {
        parent::__clone();
        $this->sqlFields = [];
        $this->sqlGroupBy = [];
    }
    
    /**
     * Gets the Tables object for this query.
     *
     * @param \Drupal\Core\Database\Query\SelectInterface $sql_query
     *   The SQL query object being built.
     *
     * @return \Drupal\Core\Entity\Query\Sql\TablesInterface
     *   The object that adds tables and fields to the SQL query object.
     */
    public function getTables(SelectInterface $sql_query) {
        $class = static::getClass($this->namespaces, 'Tables');
        return new $class($sql_query);
    }
    
    /**
     * Implements the magic __toString method.
     */
    public function __toString() {
        // Clone the query so the prepare and compile doesn't get repeated.
        $clone = clone $this;
        $clone->prepare()
            ->compile()
            ->addSort()
            ->finish();
        // Quote arguments so query is able to be run.
        $quoted = [];
        foreach ($clone->sqlQuery
            ->getArguments() as $key => $value) {
            $quoted[$key] = is_null($value) ? 'NULL' : $this->connection
                ->quote($value);
        }
        // Replace table name brackets.
        $sql = $clone->connection
            ->prefixTables((string) $clone->sqlQuery);
        return strtr($sql, $quoted);
    }

}