type ScrollAlignment = 'start' | 'center' | 'end' | 'auto';

interface ScrollToOptions {
  align: ScrollAlignment;
}

interface ScrollToOffsetOptions extends ScrollToOptions {}
interface ScrollToIndexOptions extends ScrollToOptions {}

type Key = number | string;

export type VirtualItem = {
  key: Key;
  index: number;
  start: number;
  end: number;
  size: number;
  measureRef: (el: HTMLElement | null) => void;
};

export interface Range {
  start: number;
  end: number;
  overscan: number;
  size: number;
}

declare function defaultRangeExtractor(range: Range): number[];

interface Rect {
  width: number;
  height: number;
}

interface ScrollOptions<T> {
  parentRef: React.RefObject<T>;
  windowRef?: React.RefObject<Window>;
  horizontal?: boolean;
  useObserver?: (ref: React.RefObject<T>, initialRect?: Rect) => Rect;
  useWindowObserver?: (ref: React.RefObject<Window>, initialRect?: Rect) => Rect;
  initialRect?: Rect;
}

declare function useDefaultScroll<T>(options: ScrollOptions<T>): {
  outerSize: number;
  scrollOffset: number;
  scrollToFn: (offset: number, reason: ScrollReason) => void;
};

type ScrollReason = 'ToIndex' | 'ToOffset' | 'SizeChanged';

export interface Options<T> extends ScrollOptions<T> {
  size: number;
  estimateSize?: (index: number) => number;
  overscan?: number;
  scrollToFn?: (offset: number, defaultScrollToFn?: (offset: number) => void) => void;
  paddingStart?: number;
  paddingEnd?: number;
  keyExtractor?: (index: number) => Key;
  rangeExtractor?: (range: Range) => number[];
  useScroll?: typeof useDefaultScroll;
}

declare function useVirtual<T>(options: Options<T>): {
  virtualItems: VirtualItem[];
  totalSize: number;
  scrollToOffset: (index: number, options?: ScrollToOffsetOptions) => void;
  scrollToIndex: (index: number, options?: ScrollToIndexOptions) => void;
  measure: () => void;
};

export { defaultRangeExtractor, useVirtual, useDefaultScroll };