import type { ICarouselInstance } from 'react-native-reanimated-carousel';

type CarouselPaginationScrollAction = NonNullable<Parameters<ICarouselInstance['scrollTo']>[0]>;

/**
 * Resolves the shortest `scrollTo` action for pagination dot presses.
 *
 * In loop mode the library's absolute `scrollTo({ index })` can animate through every
 * slide when the current index is past the halfway point of the loop buffer (e.g. index 2 → 3
 * with four items). Relative `count` navigation avoids that wrap-around path.
 */
export function resolveCarouselPaginationScrollAction(
  currentIndex: number,
  targetIndex: number,
  dataLength: number,
  loop: boolean,
): CarouselPaginationScrollAction | null {
  if (currentIndex === targetIndex) return null;

  if (!loop) {
    return { index: targetIndex, animated: true };
  }

  const forwardDelta = (targetIndex - currentIndex + dataLength) % dataLength;
  const backwardDelta = (currentIndex - targetIndex + dataLength) % dataLength;

  if (forwardDelta <= backwardDelta) {
    return { count: forwardDelta, animated: true };
  }

  return { count: -backwardDelta, animated: true };
}