let isRunning = ref false

let start base ~onStart ~onEnd =
  if not !isRunning then
    let () = isRunning := true in
    let () = onStart () in
    let () = Element.setClassName base "g-Animation" in
    let delay = 400 in
    let _ =
      Js.Global.setTimeout
        (fun () ->
          let () = Element.setClassName base "" in
          let () = onEnd () in
          isRunning := false)
        delay
    in
    ()
  else ()

let replaceChild scrollBase base mkChild =
  start base
    ~onStart:(fun _ ->
      let () = Element.setScrollTop scrollBase 0 in
      Element.appendChild base (mkChild ()))
    ~onEnd:(fun _ ->
      let _ = Element.removeFirstChild base in
      ())