yaak-mountain-loop/src-web/components/core/tree/TreeIndentGuide.tsx

import classNames from "classnames";
import { useAtomValue } from "jotai";
import { memo } from "react";
import { hoveredParentDepthFamily, isAncestorHoveredFamily } from "./atoms";

export const TreeIndentGuide = memo(function TreeIndentGuide({
  treeId,
  depth,
  ancestorIds,
}: {
  treeId: string;
  depth: number;
  ancestorIds: string[];
}) {
  const parentDepth = useAtomValue(hoveredParentDepthFamily(treeId));
  const isHovered = useAtomValue(isAncestorHoveredFamily({ treeId, ancestorIds }));

  return (
    <div className="flex">
      {Array.from({ length: depth }).map((_, i) => (
        <div
          // oxlint-disable-next-line react/no-array-index-key
          key={i}
          className={classNames(
            "w-[calc(1rem+0.5px)] border-r border-r-text-subtlest",
            !(parentDepth === i + 1 && isHovered) && "opacity-30",
          )}
        />
      ))}
    </div>
  );
});