class StatementPrefetch

class StatementPrefetch implements \Iterator, StatementInterface {
    
    /**
     * The query string.
     *
     * @var string
     */
    protected $queryString;
    
    /**
     * Driver-specific options. Can be used by child classes.
     *
     * @var array
     */
    protected $driverOptions;
    
    /**
     * The Drupal database connection object.
     *
     * @var \Drupal\Core\Database\Connection
     */
    protected $connection;
    
    /**
     * Reference to the PDO connection object for this statement.
     *
     * @var \PDO
     */
    protected $pdoConnection;
    
    /**
     * Main data store.
     *
     * @var array
     */
    protected $data = [];
    
    /**
     * The current row, retrieved in \PDO::FETCH_ASSOC format.
     *
     * @var array
     */
    protected $currentRow = NULL;
    
    /**
     * The key of the current row.
     *
     * @var int
     */
    protected $currentKey = NULL;
    
    /**
     * The list of column names in this result set.
     *
     * @var array
     */
    protected $columnNames = NULL;
    
    /**
     * The number of rows matched by the last query.
     *
     * @var int
     */
    protected $rowCount = NULL;
    
    /**
     * The number of rows in this result set.
     *
     * @var int
     */
    protected $resultRowCount = 0;
    
    /**
     * Holds the current fetch style (which will be used by the next fetch).
     * @see \PDOStatement::fetch()
     *
     * @var int
     */
    protected $fetchStyle = \PDO::FETCH_OBJ;
    
    /**
     * Holds supplementary current fetch options (which will be used by the next fetch).
     *
     * @var array
     */
    protected $fetchOptions = [
        'class' => 'stdClass',
        'constructor_args' => [],
        'object' => NULL,
        'column' => 0,
    ];
    
    /**
     * Holds the default fetch style.
     *
     * @var int
     */
    protected $defaultFetchStyle = \PDO::FETCH_OBJ;
    
    /**
     * Holds supplementary default fetch options.
     *
     * @var array
     */
    protected $defaultFetchOptions = [
        'class' => 'stdClass',
        'constructor_args' => [],
        'object' => NULL,
        'column' => 0,
    ];
    
    /**
     * Is rowCount() execution allowed.
     *
     * @var bool
     */
    protected $rowCountEnabled = FALSE;
    
    /**
     * Constructs a StatementPrefetch object.
     *
     * @param \PDO $pdo_connection
     *   An object of the PDO class representing a database connection.
     * @param \Drupal\Core\Database\Connection $connection
     *   The database connection.
     * @param string $query
     *   The query string.
     * @param array $driver_options
     *   Driver-specific options.
     * @param bool $row_count_enabled
     *   (optional) Enables counting the rows matched. Defaults to FALSE.
     */
    public function __construct(\PDO $pdo_connection, Connection $connection, $query, array $driver_options = [], bool $row_count_enabled = FALSE) {
        $this->pdoConnection = $pdo_connection;
        $this->connection = $connection;
        $this->queryString = $query;
        $this->driverOptions = $driver_options;
        $this->rowCountEnabled = $row_count_enabled;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getConnectionTarget() : string {
        return $this->connection
            ->getTarget();
    }
    
    /**
     * {@inheritdoc}
     */
    public function execute($args = [], $options = []) {
        if (isset($options['fetch'])) {
            if (is_string($options['fetch'])) {
                // Default to an object. Note: db fields will be added to the object
                // before the constructor is run. If you need to assign fields after
                // the constructor is run. See https://www.drupal.org/node/315092.
                $this->setFetchMode(\PDO::FETCH_CLASS, $options['fetch']);
            }
            else {
                $this->setFetchMode($options['fetch']);
            }
        }
        if ($this->connection
            ->isEventEnabled(StatementExecutionStartEvent::class)) {
            $startEvent = new StatementExecutionStartEvent(spl_object_id($this), $this->connection
                ->getKey(), $this->connection
                ->getTarget(), $this->getQueryString(), $args ?? [], $this->connection
                ->findCallerFromDebugBacktrace());
            $this->connection
                ->dispatchEvent($startEvent);
        }
        // Prepare the query.
        $statement = $this->getStatement($this->queryString, $args);
        if (!$statement) {
            $this->throwPDOException();
        }
        $return = $statement->execute($args);
        if (!$return) {
            $this->throwPDOException();
        }
        if ($this->rowCountEnabled) {
            $this->rowCount = $statement->rowCount();
        }
        // Fetch all the data from the reply, in order to release any lock
        // as soon as possible.
        $this->data = $statement->fetchAll(\PDO::FETCH_ASSOC);
        // Destroy the statement as soon as possible. See the documentation of
        // \Drupal\sqlite\Driver\Database\sqlite\Statement for an explanation.
        unset($statement);
        $this->resultRowCount = count($this->data);
        if ($this->resultRowCount) {
            $this->columnNames = array_keys($this->data[0]);
        }
        else {
            $this->columnNames = [];
        }
        if (isset($startEvent) && $this->connection
            ->isEventEnabled(StatementExecutionEndEvent::class)) {
            $this->connection
                ->dispatchEvent(new StatementExecutionEndEvent($startEvent->statementObjectId, $startEvent->key, $startEvent->target, $startEvent->queryString, $startEvent->args, $startEvent->caller, $startEvent->time));
        }
        // Initialize the first row in $this->currentRow.
        $this->next();
        return $return;
    }
    
    /**
     * Throw a PDO Exception based on the last PDO error.
     */
    protected function throwPDOException() {
        $error_info = $this->connection
            ->errorInfo();
        // We rebuild a message formatted in the same way as PDO.
        $exception = new \PDOException("SQLSTATE[" . $error_info[0] . "]: General error " . $error_info[1] . ": " . $error_info[2]);
        $exception->errorInfo = $error_info;
        throw $exception;
    }
    
    /**
     * Grab a PDOStatement object from a given query and its arguments.
     *
     * Some drivers (including SQLite) will need to perform some preparation
     * themselves to get the statement right.
     *
     * @param $query
     *   The query.
     * @param array|null $args
     *   An array of arguments. This can be NULL.
     *
     * @return \PDOStatement
     *   A PDOStatement object.
     */
    protected function getStatement($query, &$args = []) {
        return $this->connection
            ->prepare($query, $this->driverOptions);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getQueryString() {
        return $this->queryString;
    }
    
    /**
     * {@inheritdoc}
     */
    public function setFetchMode($mode, $a1 = NULL, $a2 = []) {
        $this->defaultFetchStyle = $mode;
        switch ($mode) {
            case \PDO::FETCH_CLASS:
                $this->defaultFetchOptions['class'] = $a1;
                if ($a2) {
                    $this->defaultFetchOptions['constructor_args'] = $a2;
                }
                break;
            case \PDO::FETCH_COLUMN:
                $this->defaultFetchOptions['column'] = $a1;
                break;
            case \PDO::FETCH_INTO:
                $this->defaultFetchOptions['object'] = $a1;
                break;
        }
        // Set the values for the next fetch.
        $this->fetchStyle = $this->defaultFetchStyle;
        $this->fetchOptions = $this->defaultFetchOptions;
    }
    
    /**
     * Return the current row formatted according to the current fetch style.
     *
     * This is the core method of this class. It grabs the value at the current
     * array position in $this->data and format it according to $this->fetchStyle
     * and $this->fetchMode.
     *
     * @return mixed
     *   The current row formatted as requested.
     */
    public function current() {
        if (isset($this->currentRow)) {
            switch ($this->fetchStyle) {
                case \PDO::FETCH_ASSOC:
                    return $this->currentRow;
                case \PDO::FETCH_BOTH:
                    // \PDO::FETCH_BOTH returns an array indexed by both the column name
                    // and the column number.
                    return $this->currentRow + array_values($this->currentRow);
                case \PDO::FETCH_NUM:
                    return array_values($this->currentRow);
                case \PDO::FETCH_LAZY:
                // We do not do lazy as everything is fetched already. Fallback to
                // \PDO::FETCH_OBJ.
                case \PDO::FETCH_OBJ:
                    return (object) $this->currentRow;
                case \PDO::FETCH_CLASS | \PDO::FETCH_CLASSTYPE:
                    $class_name = array_shift($this->currentRow);
                // Deliberate no break.
                case \PDO::FETCH_CLASS:
                    if (!isset($class_name)) {
                        $class_name = $this->fetchOptions['class'];
                    }
                    if (count($this->fetchOptions['constructor_args'])) {
                        $reflector = new \ReflectionClass($class_name);
                        $result = $reflector->newInstanceArgs($this->fetchOptions['constructor_args']);
                    }
                    else {
                        $result = new $class_name();
                    }
                    foreach ($this->currentRow as $k => $v) {
                        $result->{$k} = $v;
                    }
                    return $result;
                case \PDO::FETCH_INTO:
                    foreach ($this->currentRow as $k => $v) {
                        $this->fetchOptions['object']->{$k} = $v;
                    }
                    return $this->fetchOptions['object'];
                case \PDO::FETCH_COLUMN:
                    if (isset($this->columnNames[$this->fetchOptions['column']])) {
                        return $this->currentRow[$this->columnNames[$this->fetchOptions['column']]];
                    }
                    else {
                        return;
                    }
            }
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function key() {
        return $this->currentKey;
    }
    
    /**
     * {@inheritdoc}
     */
    public function rewind() {
        // Nothing to do: our DatabaseStatement can't be rewound.
    }
    
    /**
     * {@inheritdoc}
     */
    public function next() {
        if (!empty($this->data)) {
            $this->currentRow = reset($this->data);
            $this->currentKey = key($this->data);
            unset($this->data[$this->currentKey]);
        }
        else {
            $this->currentRow = NULL;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function valid() {
        return isset($this->currentRow);
    }
    
    /**
     * {@inheritdoc}
     */
    public function rowCount() {
        // SELECT query should not use the method.
        if ($this->rowCountEnabled) {
            return $this->rowCount;
        }
        else {
            throw new RowCountException();
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function fetch($fetch_style = NULL, $cursor_orientation = \PDO::FETCH_ORI_NEXT, $cursor_offset = NULL) {
        if (isset($this->currentRow)) {
            // Set the fetch parameter.
            $this->fetchStyle = $fetch_style ?? $this->defaultFetchStyle;
            $this->fetchOptions = $this->defaultFetchOptions;
            // Grab the row in the format specified above.
            $return = $this->current();
            // Advance the cursor.
            $this->next();
            // Reset the fetch parameters to the value stored using setFetchMode().
            $this->fetchStyle = $this->defaultFetchStyle;
            $this->fetchOptions = $this->defaultFetchOptions;
            return $return;
        }
        else {
            return FALSE;
        }
    }
    public function fetchColumn($index = 0) {
        if (isset($this->currentRow) && isset($this->columnNames[$index])) {
            // We grab the value directly from $this->data, and format it.
            $return = $this->currentRow[$this->columnNames[$index]];
            $this->next();
            return $return;
        }
        else {
            return FALSE;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function fetchField($index = 0) {
        return $this->fetchColumn($index);
    }
    
    /**
     * {@inheritdoc}
     */
    public function fetchObject(?string $class_name = NULL, array $constructor_arguments = []) {
        if (isset($this->currentRow)) {
            if (!isset($class_name)) {
                // Directly cast to an object to avoid a function call.
                $result = (object) $this->currentRow;
            }
            else {
                $this->fetchStyle = \PDO::FETCH_CLASS;
                $this->fetchOptions = [
                    'class' => $class_name,
                    'constructor_args' => $constructor_arguments,
                ];
                // Grab the row in the format specified above.
                $result = $this->current();
                // Reset the fetch parameters to the value stored using setFetchMode().
                $this->fetchStyle = $this->defaultFetchStyle;
                $this->fetchOptions = $this->defaultFetchOptions;
            }
            $this->next();
            return $result;
        }
        else {
            return FALSE;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function fetchAssoc() {
        if (isset($this->currentRow)) {
            $result = $this->currentRow;
            $this->next();
            return $result;
        }
        else {
            return FALSE;
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function fetchAll($mode = NULL, $column_index = NULL, $constructor_arguments = NULL) {
        $this->fetchStyle = $mode ?? $this->defaultFetchStyle;
        $this->fetchOptions = $this->defaultFetchOptions;
        if (isset($column_index)) {
            $this->fetchOptions['column'] = $column_index;
        }
        if (isset($constructor_arguments)) {
            $this->fetchOptions['constructor_args'] = $constructor_arguments;
        }
        $result = [];
        // Traverse the array as PHP would have done.
        while (isset($this->currentRow)) {
            // Grab the row in the format specified above.
            $result[] = $this->current();
            $this->next();
        }
        // Reset the fetch parameters to the value stored using setFetchMode().
        $this->fetchStyle = $this->defaultFetchStyle;
        $this->fetchOptions = $this->defaultFetchOptions;
        return $result;
    }
    
    /**
     * {@inheritdoc}
     */
    public function fetchCol($index = 0) {
        if (isset($this->columnNames[$index])) {
            $result = [];
            // Traverse the array as PHP would have done.
            while (isset($this->currentRow)) {
                $result[] = $this->currentRow[$this->columnNames[$index]];
                $this->next();
            }
            return $result;
        }
        else {
            return [];
        }
    }
    
    /**
     * {@inheritdoc}
     */
    public function fetchAllKeyed($key_index = 0, $value_index = 1) {
        if (!isset($this->columnNames[$key_index]) || !isset($this->columnNames[$value_index])) {
            return [];
        }
        $key = $this->columnNames[$key_index];
        $value = $this->columnNames[$value_index];
        $result = [];
        // Traverse the array as PHP would have done.
        while (isset($this->currentRow)) {
            $result[$this->currentRow[$key]] = $this->currentRow[$value];
            $this->next();
        }
        return $result;
    }
    
    /**
     * {@inheritdoc}
     */
    public function fetchAllAssoc($key, $fetch_style = NULL) {
        $this->fetchStyle = $fetch_style ?? $this->defaultFetchStyle;
        $this->fetchOptions = $this->defaultFetchOptions;
        $result = [];
        // Traverse the array as PHP would have done.
        while (isset($this->currentRow)) {
            // Grab the row in its raw \PDO::FETCH_ASSOC format.
            $result_row = $this->current();
            $result[$this->currentRow[$key]] = $result_row;
            $this->next();
        }
        // Reset the fetch parameters to the value stored using setFetchMode().
        $this->fetchStyle = $this->defaultFetchStyle;
        $this->fetchOptions = $this->defaultFetchOptions;
        return $result;
    }

}