import type { ListItemProps } from "./types";

export function useList<Item>({
  items,
  width,
  height,
  overscanBy = 2,
  scrollTop,
  itemHeight,
  itemGap = 0,
}: UseListOptions<Item>) {
  const totalItemHeight = itemHeight + itemGap;
  overscanBy = height * overscanBy;
  let index = Math.floor(
    Math.max(0, scrollTop - overscanBy / 2) / totalItemHeight
  );
  const stopIndex = Math.min(
    items.length,
    Math.ceil((scrollTop + overscanBy) / totalItemHeight)
  );
  const childProps: ListItemProps<Item>[] = [];

  for (; index < stopIndex; index++) {
    childProps.push({
      index,
      data: items[index],
      width,
      height,
      style: {
        position: "absolute",
        width: "100%",
        top: itemGap * index + index * itemHeight,
        left: 0,
      },
    });
  }

  return childProps;
}

export interface UseListOptions<Item> {
  items: Item[];
  width: number;
  height: number;
  itemHeight: number;
  itemGap?: number;
  overscanBy?: number;
  scrollTop: number;
}