tolaria/src/components/ResizeHandle.tsx

import { useCallback, useEffect, useRef } from 'react'

interface ResizeHandleProps {
  onResize: (delta: number) => void
}

export function ResizeHandle({ onResize }: ResizeHandleProps) {
  const isDragging = useRef(false)
  const lastX = useRef(0)
  const pendingDelta = useRef(0)
  const rafId = useRef(0)

  const handleMouseDown = useCallback(
    (e: React.MouseEvent) => {
      e.preventDefault()
      isDragging.current = true
      lastX.current = e.clientX
      pendingDelta.current = 0
      document.body.style.cursor = 'col-resize'
      document.body.style.userSelect = 'none'
    },
    [],
  )

  useEffect(() => {
    const handleMouseMove = (e: MouseEvent) => {
      if (!isDragging.current) return
      pendingDelta.current += e.clientX - lastX.current
      lastX.current = e.clientX

      if (!rafId.current) {
        rafId.current = requestAnimationFrame(() => {
          if (pendingDelta.current !== 0) {
            onResize(pendingDelta.current)
            pendingDelta.current = 0
          }
          rafId.current = 0
        })
      }
    }

    const handleMouseUp = () => {
      if (isDragging.current) {
        isDragging.current = false
        document.body.style.cursor = ''
        document.body.style.userSelect = ''
        // Flush any pending delta
        if (rafId.current) {
          cancelAnimationFrame(rafId.current)
          rafId.current = 0
        }
        if (pendingDelta.current !== 0) {
          onResize(pendingDelta.current)
          pendingDelta.current = 0
        }
      }
    }

    document.addEventListener('mousemove', handleMouseMove)
    document.addEventListener('mouseup', handleMouseUp)
    return () => {
      document.removeEventListener('mousemove', handleMouseMove)
      document.removeEventListener('mouseup', handleMouseUp)
      if (rafId.current) cancelAnimationFrame(rafId.current)
    }
  }, [onResize])

  return (
    <div
      className="-ml-1 w-1 shrink-0 cursor-col-resize bg-transparent transition-colors hover:bg-[var(--border)]"
      onMouseDown={handleMouseDown}
    />
  )
}