offline.eliom

let down_of_react = Eliom_react.S.Down.of_react

let time_update_signal, do_time_update = React.S.create 0.0

let offline_time = 60.

let _ =
  let t = Unix.time () in
  while%lwt true do
    let%lwt _ = Lwt_unix.sleep offline_time in
    do_time_update (Unix.time () -. t);
    Lwt.return_unit
  done

let time_update_signal = down_of_react time_update_signal

[%%client

  let time_update_signal_client, do_time_update_client = React.S.create (((new%js Js.date_now)##getTime)/.1000.)

  let _ =
    while%lwt true do
      let%lwt _ = Lwt_js.sleep ~%offline_time in
      let d = new%js Js.date_now in
      let f = (d##getTime)/.1000. in
      do_time_update_client f;
      Lwt.return_unit
    done

  let is_connected =
    let init_server = React.S.value ~%time_update_signal in
    let init_client = React.S.value time_update_signal_client in
    React.S.l2 (fun fs fc ->
      let diff = abs_float @@  (fs -. fc) -. (init_server -. init_client)
      in
      diff < 4. *. ~%offline_time) ~%time_update_signal time_update_signal_client


  (*let _ = React.S.map (fun b ->
    if not b then
      Js.Unsafe.eval_string @@ "alert('Network disconnected.')";) is_connected
          |> Lwt_react.S.keep*)

  open Lwt
  let persistent_of_react n a = a

  let if_online: string -> (unit -> 'a React.signal) -> 'a -> 'a React.signal = fun name a b ->
    let b = 
    Js.Optdef.case Dom_html.window##.localStorage (fun () ->
      b)
      (fun localStorage ->
         Js.Opt.case (localStorage##getItem (Js.string name)) (fun () ->
           b)
           (fun a ->
              let b:'a = Json.unsafe_input a in
              b
           )
      )
    in
    let getter, setter = React.S.create b in
    Lwt.async (fun () ->
      let result = a () in
      React.S.map (fun result ->
        let%lwt () = Js.Optdef.case Dom_html.window##.localStorage (fun () ->
          Lwt_log_js.warning "localstorage not defined, nothing in cache")
          (fun localStorage ->
             Lwt.return @@ localStorage##setItem (Js.string name) (Json.output result)) in
        Lwt.return (setter result)) result |> Lwt_react.S.keep |> return
      );
    setter b; getter
]