trait StatementIteratorTrait

trait StatementIteratorTrait {
    
    /**
     * Traces if rows can be fetched from the resultset.
     */
    private bool $isResultsetIterable = FALSE;
    
    /**
     * The current row, retrieved in the current fetch format.
     */
    private mixed $resultsetRow = NULL;
    
    /**
     * The key of the current row.
     *
     * This keeps the index of rows fetched from the underlying statement. It is
     * set to -1 when no rows have been fetched yet.
     */
    private int $resultsetKey = -1;
    
    /**
     * Informs the iterator whether rows can be fetched from the resultset.
     *
     * @param bool $valid
     *   The result of the execution of the client statement.
     */
    protected function markResultsetIterable(bool $valid) : void {
        $this->isResultsetIterable = $valid;
        $this->resultsetRow = NULL;
        if ($valid === TRUE) {
            $this->resultsetKey = -1;
        }
    }
    
    /**
     * Sets the current resultset row for the iterator, and increments the key.
     *
     * @param mixed $row
     *   The last row fetched from the client statement.
     */
    protected function setResultsetCurrentRow(mixed $row) : void {
        $this->resultsetRow = $row;
        $this->resultsetKey++;
    }
    
    /**
     * Returns the row index of the current element in the resultset.
     *
     * @return int
     *   The row index of the current element in the resultset.
     */
    protected function getResultsetCurrentRowIndex() : int {
        return $this->resultsetKey;
    }
    
    /**
     * Informs the iterator that no more rows can be fetched from the resultset.
     */
    protected function markResultsetFetchingComplete() : void {
        $this->markResultsetIterable(FALSE);
    }
    
    /**
     * Returns the current element.
     *
     * @see https://www.php.net/manual/en/iterator.current.php
     *
     * @internal This method should not be called directly.
     */
    public function current() : mixed {
        return $this->resultsetRow;
    }
    
    /**
     * Returns the key of the current element.
     *
     * @see https://www.php.net/manual/en/iterator.key.php
     *
     * @internal This method should not be called directly.
     */
    public function key() : mixed {
        return $this->resultsetKey;
    }
    
    /**
     * Rewinds back to the first element of the Iterator.
     *
     * This is the first method called when starting a foreach loop. It will not
     * be executed after foreach loops.
     *
     * @see https://www.php.net/manual/en/iterator.rewind.php
     *
     * @internal This method should not be called directly.
     */
    public function rewind() : void {
        // Nothing to do: our DatabaseStatement can't be rewound. Error out when
        // attempted.
        // @todo convert the error to an exception in Drupal 11.
        if ($this->resultsetKey >= 0) {
            trigger_error('Attempted rewinding a StatementInterface object when fetching has already started. Refactor your code to avoid rewinding statement objects.', E_USER_WARNING);
            $this->markResultsetIterable(FALSE);
        }
    }
    
    /**
     * Moves the current position to the next element.
     *
     * This method is called after each foreach loop.
     *
     * @see https://www.php.net/manual/en/iterator.next.php
     *
     * @internal This method should not be called directly.
     */
    public function next() : void {
        $this->fetch();
    }
    
    /**
     * Checks if current position is valid.
     *
     * This method is called after ::rewind() and ::next() to check if the
     * current position is valid.
     *
     * @see https://www.php.net/manual/en/iterator.valid.php
     *
     * @internal This method should not be called directly.
     */
    public function valid() : bool {
        if ($this->isResultsetIterable && $this->resultsetKey === -1) {
            $this->fetch();
        }
        return $this->isResultsetIterable;
    }

}