class OffsetPage

class OffsetPage {
    
    /**
     * The JSON:API pagination key name.
     *
     * @var string
     */
    const KEY_NAME = 'page';
    
    /**
     * The offset key in the page parameter: page[offset].
     *
     * @var string
     */
    const OFFSET_KEY = 'offset';
    
    /**
     * The size key in the page parameter: page[limit].
     *
     * @var string
     */
    const SIZE_KEY = 'limit';
    
    /**
     * Default offset.
     *
     * @var int
     */
    const DEFAULT_OFFSET = 0;
    
    /**
     * Max size.
     *
     * @var int
     */
    const SIZE_MAX = 50;
    
    /**
     * The offset for the query.
     *
     * @var int
     */
    protected $offset;
    
    /**
     * The size of the query.
     *
     * @var int
     */
    protected $size;
    
    /**
     * Instantiates an OffsetPage object.
     *
     * @param int $offset
     *   The query offset.
     * @param int $size
     *   The query size limit.
     */
    public function __construct($offset, $size) {
        $this->offset = $offset;
        $this->size = $size;
    }
    
    /**
     * Returns the current offset.
     *
     * @return int
     *   The query offset.
     */
    public function getOffset() {
        return $this->offset;
    }
    
    /**
     * Returns the page size.
     *
     * @return int
     *   The requested size of the query result.
     */
    public function getSize() {
        return $this->size;
    }
    
    /**
     * Creates an OffsetPage object from a query parameter.
     *
     * @param mixed $parameter
     *   The `page` query parameter from the Symfony request object.
     *
     * @return static
     *   An OffsetPage object with defaults.
     */
    public static function createFromQueryParameter($parameter) {
        if (!is_array($parameter)) {
            $cacheability = (new CacheableMetadata())->addCacheContexts([
                'url.query_args:page',
            ]);
            throw new CacheableBadRequestHttpException($cacheability, 'The page parameter needs to be an array.');
        }
        $expanded = $parameter + [
            static::OFFSET_KEY => static::DEFAULT_OFFSET,
            static::SIZE_KEY => static::SIZE_MAX,
        ];
        if ($expanded[static::SIZE_KEY] > static::SIZE_MAX) {
            $expanded[static::SIZE_KEY] = static::SIZE_MAX;
        }
        return new static($expanded[static::OFFSET_KEY], $expanded[static::SIZE_KEY]);
    }

}