bsky-social-app/src/lib/hooks/useDraggableScrollView.ts

import {type ForwardedRef, useEffect, useMemo, useRef} from 'react'
import {type ScrollView} from 'react-native'
import {Platform} from 'react-native'

import {mergeRefs} from '#/lib/merge-refs'

type Props<Scrollable extends ScrollView = ScrollView> = {
  cursor?: string
  outerRef?: ForwardedRef<Scrollable>
}

export function useDraggableScroll<Scrollable extends ScrollView = ScrollView>({
  outerRef,
  cursor = 'grab',
}: Props<Scrollable> = {}) {
  const ref = useRef<Scrollable>(null)

  useEffect(() => {
    if (Platform.OS !== 'web' || !ref.current) {
      return
    }
    const slider = ref.current as unknown as HTMLDivElement
    if (!slider) {
      return
    }
    let isDragging = false
    let isMouseDown = false
    let startX = 0
    let scrollLeft = 0

    const mouseDown = (e: MouseEvent) => {
      isMouseDown = true
      startX = e.pageX - slider.offsetLeft
      scrollLeft = slider.scrollLeft

      slider.style.cursor = cursor
    }

    const mouseUp = () => {
      if (isDragging) {
        slider.addEventListener('click', e => e.stopPropagation(), {once: true})
      }

      isMouseDown = false
      isDragging = false
      slider.style.cursor = 'default'
    }

    const mouseMove = (e: MouseEvent) => {
      if (!isMouseDown) {
        return
      }

      // Require n pixels momement before start of drag (3 in this case )
      const x = e.pageX - slider.offsetLeft
      if (Math.abs(x - startX) < 3) {
        return
      }

      isDragging = true
      e.preventDefault()
      const walk = x - startX
      slider.scrollLeft = scrollLeft - walk
    }

    slider.addEventListener('mousedown', mouseDown)
    window.addEventListener('mouseup', mouseUp)
    window.addEventListener('mousemove', mouseMove)

    return () => {
      slider.removeEventListener('mousedown', mouseDown)
      window.removeEventListener('mouseup', mouseUp)
      window.removeEventListener('mousemove', mouseMove)
    }
  }, [cursor])

  const refs = useMemo(
    () => mergeRefs(outerRef ? [ref, outerRef] : [ref]),
    [ref, outerRef],
  )

  return {
    refs,
  }
}