scrollMania, mobile safari viewport scroll shenanigans

scrollMania.js

const scrollMania = () => {
    const currentScroll = window.pageYOffset || document.documentElement.scrollTop
    // a 100vh element minus the actual height of the window(aka viewport)
    const testThreshold = heightRef.current.offsetHeight - window.innerHeight

    const end = () => {
      if(currentScroll !== scrollDelta) {
        setScrollDelta(currentScroll)
      }
      return true
    }

    /****************************/

    if(window.innerHeight !== canvasElement.current.offsetHeight) {
      setM('')
      // down? near top?
      if(currentScroll > scrollDelta && currentScroll > 0 && currentScroll < testThreshold) {
        setTest(false)
      } else {
        setTest(true)
      }
      return end()
    }

    // up
    if(currentScroll < scrollDelta && window.innerHeight === canvasElement.current.offsetHeight){
      setM('up - not enough')
      setTest(false)
      return end()
    }

    // up
    if(currentScroll < scrollDelta && window.innerHeight !== canvasElement.current.offsetHeight){
      setM('up')
      setTest(true)
      return end()
    }

    // down
    if(currentScroll > scrollDelta) { // scrolling down
      setM('down')
      setTest(false)
      return end()
    }
  }