markdown-converter/src/renderer/hooks/use-scroll-sync.ts

import { useCallback, useRef } from 'react';

interface Options {
  onEditorScroll?: (ratio: number) => void;
  onPreviewScroll?: (ratio: number) => void;
}

export function useScrollSync(opts: Options) {
  const FRAME_MS = 1000 / 60;
  const lastTick = useRef(-FRAME_MS);

  const handleEditorScroll = useCallback((evt: React.UIEvent<HTMLElement>) => {
    const target = evt.currentTarget;
    const ratio = target.scrollTop / Math.max(target.scrollHeight - target.clientHeight, 1);
    const now = performance.now();
    if (now - lastTick.current < FRAME_MS) return;
    lastTick.current = now;
    opts.onEditorScroll?.(ratio);
  }, [opts]);

  const handlePreviewScroll = useCallback((evt: React.UIEvent<HTMLElement>) => {
    const target = evt.currentTarget;
    const ratio = target.scrollTop / Math.max(target.scrollHeight - target.clientHeight, 1);
    opts.onPreviewScroll?.(ratio);
  }, [opts]);

  return { handleEditorScroll, handlePreviewScroll };
}